CN111534068A - Polylactic acid material with ultrahigh impact strength and preparation method thereof - Google Patents

Polylactic acid material with ultrahigh impact strength and preparation method thereof Download PDF

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CN111534068A
CN111534068A CN202010493344.6A CN202010493344A CN111534068A CN 111534068 A CN111534068 A CN 111534068A CN 202010493344 A CN202010493344 A CN 202010493344A CN 111534068 A CN111534068 A CN 111534068A
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polylactic acid
stretching
temperature
impact strength
strain
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CN111534068B (en
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王志刚
王佳
王学会
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University of Science and Technology of China USTC
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    • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
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Abstract

The invention provides a polylactic acid material with ultrahigh impact strength and a preparation method thereof. The polylactic acid material with ultrahigh impact strength provided by the invention takes the elastomer or the plastic as the toughening agent, and after the elastomer or the plastic is uniformly blended to form a parison, the parison is stretched above the glass transition temperature of the parison, so that the impact resistance of the polylactic acid/elastomer or polylactic acid/plastic blended material is obviously improved. Experimental results show that the breaking strength of the polylactic acid blended material subjected to the stretching treatment is improved from 60MPa to 171MPa, the breaking elongation is improved from 6% to 17-124%, and the notch impact strength is 2KJ/m2Increased to 272KJ/m2The toughening effects of mechanical property enhancement and impact resistance are very obvious. Pulling deviceThe stretching treatment can also increase the crystallinity of the polylactic acid blended material, thereby greatly improving the heat resistance of the material.

Description

Polylactic acid material with ultrahigh impact strength and preparation method thereof
Technical Field
The invention belongs to the technical field of high polymer materials, and particularly relates to a preparation method of a polylactic acid material with ultrahigh impact strength.
Background
In recent years, with the increasing problems of resource shortage, environmental pollution and the like, the development and application of sustainable resources are receiving wide attention, and particularly, environmentally-friendly and biodegradable materials are receiving wide attention. Meanwhile, due to the rapid development of material science, the existing materials cannot meet the requirements of human beings. Therefore, it is a major trend in development to develop materials with high performance, degradability and excellent comprehensive properties and expand the application fields thereof.
Polylactic acid is an environment-friendly plastic from biomass, has the advantages of excellent biocompatibility, biodegradability, processability and the like, has the reputation of 'green plastic', and is more and more concerned by people. However, polylactic acid still has the problems of brittleness, low toughness, poor heat resistance and the like, and the notch impact strength value is lower than 4KJ/m2This severely limits the wide application of polylactic acid materials in various fields. Therefore, research on modification of polylactic acid materials is becoming a hot spot, and in particular, various toughening modifications are being performed on the polylactic acid materials.
Chinese patent CN1701082 discloses a technical scheme that polyformaldehyde and polylactic acid are blended, and an impact modifier is added to improve the impact resistance of the blend. The proposal improves the impact resistance of the mixture, and the numerical value of the notch impact strength is 128.2J/m.
Chinese patent CN107033563 discloses a reinforced and toughened polylactic acid material obtained by melt blending of a polyurethane modifier and polylactic acid, the notched impact strength value of which is 15KJ/m2。
Chinese patent CN110305457 discloses a transparent toughened polylactic acid material prepared by melt blending of silicon rubber microspheres and polylactic acid particles, the transparency of the transparent toughened polylactic acid material is basically consistent with that of pure polylactic acid, and the numerical value of unnotched impact strength is 115KJ/m2。
Chinese patent CN110305435 discloses a transparent toughened polylactic acid/acrylic alloy material prepared by melt blending of crystalline polylactic acid, polymethyl methacrylate, a transparent toughening agent and a compatilizer, wherein the numerical value of the notch impact strength of the transparent toughened polylactic acid/acrylic alloy material is 38KJ/m2。
Chinese patent CN107022181 discloses melt blending of natural rubber and polylactic acid in an attempt to toughen the polylactic acid more effectively without loss of polylactic acidRigidity and strength, but its notched impact strength is only 6KJ/m2。
Chinese patent CN105602214 discloses that polylactic acid is blended with polyethylene glycol diacetate with low molecular weight and high molecular weight simultaneously, so as to realize plasticizing and toughening effects on polylactic acid, and the elongation at break and the notch impact strength are 271 percent and 68KJ/m respectively2。
Disclosure of Invention
An object of the present invention is to provide a polylactic acid material with ultra-high impact strength and a preparation method thereof, so as to overcome the brittleness defect of polylactic acid pointed out in the introduction of the background art. The preparation method of the polylactic acid material with ultrahigh impact strength comprises the following steps: respectively drying the polylactic acid granules and the toughening agent, then adding the toughening agent under the polylactic acid melting condition for blending, obtaining a parison through hot pressing or injection molding, then stretching the parison above the glass transition temperature of the parison, and cooling and solidifying the parison below the glass transition temperature of the parison after reaching a certain strain, thereby obtaining the polylactic acid material with ultrahigh impact strength.
Preferably, the toughening agent is an elastomer or a plastic.
Preferably, the toughening agent comprises an ethylene-methyl acrylate-glycidyl methacrylate random copolymer, a hydrogenated polystyrene-polybutadiene-polystyrene triblock copolymer, an elastomer such as natural rubber or polycaprolactone plastic.
Preferably, the mass ratio of the toughening agent to the polylactic acid is 1: 1-99, preferably 1: 80-99, and more preferably 1: 80-95.
Preferably, the melt blending condition is that the blending temperature is 160-250 ℃, and the blending time is 3-30 min.
Preferably, the temperature of the stretching treatment is between the glass transition temperature of the polylactic acid blend and 90 ℃, more preferably 60-85 ℃, still more preferably 65-80 ℃.
Preferably, the stretching rate of the stretching treatment is 1 to 50mm/min, preferably 10 to 50mm/min, more preferably 20 to 50 mm/min.
Preferably, the stretching process strain of the stretching treatment is 100-700%, preferably 200-700%, more preferably 300-500%.
Another object of the present invention is to provide an ultra-high impact strength polylactic acid material, which comprises 80-99% by mass of polylactic acid and 1-20% by mass of a toughening agent, and has a breaking strength of at most 171MPa, an elongation at break of 17-124%, and at most 272KJ/m2Notched impact strength of (2). The lowest breaking strength of the polylactic acid material with ultrahigh impact strength is more than 61MPa, and the lowest notch impact strength is 115KJ/m2The above.
Drawings
FIG. 1: example 6 stress-strain graph of the stretching process;
FIG. 2: a sample object map of example 4;
FIG. 3: a sample object diagram of example 1;
FIG. 4: izod notched impact Strength plots for examples 1-6 and comparative example 1;
FIG. 5: stress-strain curves for the secondary stretches of examples 1-6 and comparative example 3;
FIG. 6: graphs of elongation at break change of the secondary stretching of examples 1 to 6 and comparative example 3;
FIG. 7: graphs of the change in rupture strength of the secondary stretching of examples 1 to 6 and comparative example 3;
FIG. 8: graph of tensile toughness change of the secondary drawing of examples 1 to 6 and comparative example 3;
FIG. 9: scanning electron micrographs of example 4;
FIG. 10: scanning electron micrographs of example 6;
FIG. 11: wide angle X-ray diffraction patterns for example 4 and comparative example 1.
FIG. 12: small angle X-ray scattering plots for example 4 and comparative example 1.
FIG. 13: the ultra small angle X-ray scatter plots of example 4 and comparative example 1.
FIG. 14: example 12 stress-strain graph of the stretching process;
FIG. 15: a sample object diagram of example 10;
FIG. 16: izod notched impact Strength plots for examples 7-11 and comparative example 2;
FIG. 17: stress-strain curves for the secondary stretches of examples 7-12 and comparative example 3;
FIG. 18: graphs of elongation at break change of the secondary stretching of examples 7 to 12 and comparative example 3;
FIG. 19: graphs of the change in rupture strength of the secondary stretching of examples 7 to 12 and comparative example 3;
FIG. 20: storage modulus versus temperature change profile in the dynamic mechanical analysis test of example 10;
FIG. 21: storage modulus versus temperature change profile in the dynamic mechanical analysis test of comparative example 2;
FIG. 22: storage modulus versus temperature change profile in the dynamic mechanical analysis test of comparative example 3.
FIG. 23: a sample object map of example 15;
FIG. 24: a sample object map of example 16;
FIG. 25: a sample object map of example 17;
FIG. 26: a sample object map of example 18;
FIG. 27 is a schematic view showing: a sample object map of example 19;
FIG. 28: a sample object diagram of example 20;
FIG. 29: sample object diagram of example 21.
Detailed Description
Definition of
The "polylactic acid pellet" described in the present application includes crystalline polylactic acid and non-crystalline polylactic acid. In the present application, the particle size, molecular weight, and molecular weight distribution of the polylactic acid are not particularly limited.
The size of the "parison" described in the present application is not particularly limited, and the "parison" is usually molded into various sizes depending on the mold in the molding press, and may be, for example, 0.5 to 16mm in thickness, 10 to 80mm in width, and 50 to 150mm in length. Depending on the size of the parison, the material to be stretch-formed may include films, sheets, blocks, etc.
The "toughener" described in the present application is not particularly limited, and an elastomer or plastic is preferably used, and examples thereof include an ethylene-methyl acrylate-glycidyl methacrylate random copolymer, a hydrogenated polystyrene-polybutadiene-polystyrene triblock copolymer, and an elastomer such as natural rubber or a polycaprolactone plastic, and the like, and a more specific example thereof is an ethylene-methyl acrylate-glycidyl methacrylate random copolymer toughener.
In the process of the present application, polylactic acid and a toughening agent (e.g., ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) or other elastomers or plastics, preferably, both the polylactic acid and the toughening agent are separately dried) are melt blended to prepare a substrate or profile, and then the blend substrate or profile is stretched above its glass transition temperature to form a strong oriented microstructure of both the elastomer or plastic particles and the polylactic acid matrix, thereby significantly improving the rigidity and toughness of the material. The polylactic acid material after the stretching treatment has the breaking strength improved from 60MPa to 171MPa, the breaking elongation improved from 6 percent to 17-124 percent and the notch impact strength improved from 2KJ/m2Increased to 272KJ/m2The reinforcing and toughening effects obtained are very significant.
In the preparation method of the present invention, "drying" treatment of the polylactic acid and the toughening agent means a general technical meaning in the field of chemical materials, that is, in order to reduce the water content-6The following.
In the production method of the present invention, the apparatus suitable for melt blending is not particularly limited, and for example, a torque rheometer may be used.
In the production method of the present invention, the cooling process used is not particularly limited, and it is usually sufficient to cool the material to room temperature. In addition, in the process of testing the tensile property of the polylactic acid material with ultrahigh impact strength, the cooling solidification after the parison is stretched is also included. Such cooling solidification is also not particularly limited in the present invention, that is, conventional cooling solidification in the art may be used.
In a specific embodiment of the present invention, the preparation method of the above polylactic acid material with ultrahigh impact strength provided by the present invention comprises:
(1) drying the raw materials at the drying temperature of 20-90 ℃ for 1-72 h. Specifically, amorphous polylactic acid needs to be dried at a relatively low temperature (23-45 ℃); the crystalline polylactic acid may be dried at 65 to 90 ℃ or may be dried by a special dehumidifying dryer for polylactic acid. The raw material is dried because it is considered that excessive moisture increases thermal degradation of polylactic acid in the step (2) and the step (3), affecting material properties.
(2) Adding 80-99 parts by mass of dried polylactic acid and 1-20 parts by mass of toughening agent into a high-speed stirrer for uniform mixing, and then adding into a double-screw extruder for melt extrusion granulation at the temperature of 160-250 ℃; melt mixing may also be carried out by an internal mixing type internal mixer or the like.
(3) Adding the obtained granules into an injection molding machine to prepare a molded product at the temperature of 160-250 ℃, wherein the temperature of a mold is set to be room temperature or 100-140 ℃, and the corresponding molding period is 20-40s or 90-120 s; the molding can also be prepared by a molding press, the molding temperature is 160-250 ℃, the pressure is 2-12MPa, and the time is 1-300 min.
(4) The parison is subjected to a stretching process in a stretching apparatus having a temperature control, the stretching temperature being above the parison glass transition temperature and below the melting temperature. Preferably, the stretching temperature is from 60 to 90 deg.C, more preferably from 60 to 85 deg.C, still more preferably from 65 to 80 deg.C. The speed is 1-50mm/min, after the strain is customized (100- & gt 700%), the polylactic acid material with ultrahigh impact strength is obtained after cooling and solidification at room temperature or below.
In the invention, the elastomer or the plastic is added into the polylactic acid matrix, and the elastomer or the plastic serving as the toughening agent can realize micron-level or submicron-level dispersion in the matrix under the action of a shear field and a temperature field, thereby achieving the purpose of partially toughening and modifying in a very limited way. However, since the strength and modulus of the elastomer or plastic itself are much lower than those of polylactic acid, the rigidity and strength of polylactic acid are reduced after the polylactic acid matrix is introduced. The introduction of the elastomer can further reduce the heat resistance of the polylactic acid, and the application of the polylactic acid is limited. In the invention, the blend is subjected to post-processing operation by using a stretching technology, so that the elastomer or plastic particles and the polylactic acid matrix are highly oriented, and a microstructure with high orientation degree is maintained, thereby not only improving the rigidity and strength of the material, but also endowing the material with ultrahigh impact strength.
The technical key points of the invention are that firstly, the polylactic acid granules and the toughening agent are melted and blended, secondly, a parison is obtained by a forming process such as hot pressing or injection molding, and thirdly, the parison is stretched above the glass transition temperature. Compared with the conventional technology in the field, no precedent for preparing the polylactic acid material with ultrahigh impact strength by adopting a stretching technology above the glass transition temperature is presented. The three-step processing method created by the invention is obtained through numerous experiments and continuous adjustment, the impact resistance of the polylactic acid material obtained by the technical scheme is the best at present, and the notch impact strength can be 2KJ/m of the polylactic acid matrix2The increase is up to 272KJ/m2And the post-stretching operation steps are simple, and the effect is very obvious.
In a particular embodiment of the present invention, there is provided a method for preparing a polylactic acid material with ultra-high impact strength, which is characterized in that: banburying the dried polylactic acid and the elastomer or the plastic according to a specific ratio, for example, banburying in a torque rheometer at a temperature of 160-250 ℃, a rotation speed of 20-200rpm, and a banburying time of 3-30min, molding the obtained blend into preforms with different sizes (thickness of 0.5-16mm, width of 10-80mm, length of 50-150mm) in a molding press at a temperature of 160-250 ℃, a pressure of 2-12MPa, and a time of 1-300min, on a stretching device with temperature control, stretching the blank at 60-90 deg.c, preferably 60-85 deg.c, more preferably 65-80 deg.c at the rate of 1-50mm/min to 100-700% customized strain, cooling and solidifying below the glass transition temperature of the polylactic acid, thereby obtaining the polylactic acid material with ultrahigh impact strength.
The polylactic acid material with ultrahigh impact strength obtained by the preparation method of the polylactic acid material with ultrahigh impact strength can be used for manufacturing packaging materials, fibers, non-woven fabrics and the like, and is mainly used in the fields of clothing (underwear and outerwear), industry (architecture, agriculture, forestry, paper making, automobile manufacturing industry), sanitary medical appliances and the like.
The invention has the beneficial effects that:
(1) the elastomer or the plastic is uniformly dispersed in the polylactic acid by melt blending in the polylactic acid body, and then the elastomer or the plastic particles and the polylactic acid matrix are highly oriented by stretching treatment above the glass transition temperature of the blend to form oriented microstructure distribution, so that the rigidity and the strength of the material are obviously improved, and the impact strength of the material is also obviously improved. The breaking strength of the polylactic acid material after stretching treatment is improved from 60MPa to 171MPa, the breaking elongation is improved from 6 percent to 17 percent to 124 percent, and the notch impact strength is improved from 2KJ/m2Increased to 272KJ/m2The reinforcing and toughening effect obtained is very significant.
(2) The melt processing of the polylactic acid matrix can realize partial limited toughening modification, the operation process is simple and easy to implement, and the toughening effect is not particularly obvious, but the stretching treatment process above the glass transition temperature can bring great improvement of the impact strength because a highly oriented microstructure is generated in a system, and oriented polylactic acid crystals are generated by stretching, so that the material is endowed with more excellent heat resistance while being enhanced and toughened, and the heat resistance temperature of the material can be obviously improved.
Examples
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that a person skilled in the art may also make several variations or modifications without departing from the inventive concept. All falling within the scope of the present invention.
The polylactic acid used in the following examples was purchased from Natureworks, Inc. under the 2003D designation, and the tougheners used were all commercially available products, such as ethylene methyl acrylate glycidyl methacrylate random copolymer (EMA-GMA) purchased from Arkema, France under the LOTADER @ AX8900 designation.
Example 1
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into preforms of 6X 15X 100mm (for the preparation of impact bars) and 3X 30X 100mm (for the preparation of secondary tensile bars), the molding temperature being 200 ℃ and the pressure 10MPa for a period of 10min, and the samples are cooled to room temperature by ice-water quenching. On a temperature-controlled stretching equipment Shenzhen Sansi company UTM2502 universal testing machine (a temperature-controlled cover is added to enable a stretching chamber to achieve constant-temperature stretching at an elevated temperature, the same is achieved in the following embodiments), a parison is stretched, the temperature of the stretching chamber is 70 ℃, the stretching rate is 20mm/min, the strain is 100%, and after the preset strain is achieved, the parison is cooled and cured in a room-temperature air environment to obtain a polylactic acid blending sample with the strain of 100%. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Fig. 3 shows that the polylactic acid material thus obtained after the stretching treatment at 70 ℃ takes a translucent shape.
Example 2
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into preforms of 6X 18X 100mm (for the preparation of impact bars) and 3X 30X 100mm (for the preparation of secondary tensile bars), the molding temperature being 200 ℃ and the pressure 10MPa for 10min, and the samples are cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 200%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Example 3
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The resulting blend was compression molded in a compression molding machine into 6X 22X 100mm (for making impact bars) and 3X 30X 100mm (for making secondary tensile bars) preforms at 200 ℃ under 10MPa for 10min, and the samples were cooled to room temperature by ice water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 300%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Example 4
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The resulting blend was compression molded in a compression molding machine into preforms of 9X 20X 100mm (for making impact bars) and 3X 30X 100mm (for making secondary tensile bars), at a compression molding temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples were cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 400%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
FIG. 2 shows the procedure of cooling and solidifying in room temperature air environment after the sample of example 4 reaches the predetermined strain.
Fig. 9 shows that alignment of the polylactic acid blend along the stretching direction can be clearly seen in the sample of example 4, resulting in an oriented structure.
FIG. 11 shows that the two-dimensional wide-angle X-ray diffraction pattern of the unstretched polylactic acid blend (comparative example 1) appears as an isotropic diffusion ring, indicating that the unstretched polylactic acid blend is amorphous and has no structural orientation. After stretching at 70 ℃, the intensity of the diffusion ring in the two-dimensional wide-angle X-ray diffraction pattern (example 4) of the polylactic acid blend parallel to the stretching direction (vertical direction) gradually becomes stronger and the intensity of the diffusion ring perpendicular to the stretching direction gradually becomes weaker as the stretching strain increases, the isotropic diffusion ring is transformed into a pair of wide diffraction arcs parallel to the stretching direction, and diffraction spots appear inside the wide diffraction arcs, indicating that the molecular chains are gradually oriented along the stretching direction during the stretching process and the orientation degree is gradually increased.
FIG. 12 shows that the two-dimensional small angle X-ray scattering pattern of the unstretched polylactic acid blend (comparative example 1) appears isotropic, indicating that the unstretched polylactic acid blend is not oriented on a nanometer scale. The two-dimensional small angle X-ray scattering pattern (example 4) after stretching at 70 ℃ shows that the molecular chains are gradually oriented in the direction of stretching during stretching as the stretching strain increases, and a highly oriented fibrillating microstructure occurs in the polylactic acid material.
FIG. 13 shows that the two-dimensional ultra-small angle X-ray scattering pattern of the unstretched polylactic acid blend (comparative example 1) appears isotropic, indicating that the unstretched polylactic acid blend is not oriented on the submicron scale. After stretching at 70 ℃, the two-dimensional ultra-small angle X-ray scattering plot (example 4) shows that as the stretching strain increases, the molecular chains gradually orient in the stretching direction during stretching, and highly oriented fibrillating submicron structures and possibly partial voiding phenomena occur in the polylactic acid material.
Example 5
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-6MA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into preforms of 6X 30X 100mm (for the preparation of impact bars) and 3X 30X 100mm (for the preparation of secondary tensile bars), the molding temperature being 200 ℃ and the pressure 10MPa for a period of 10min, and the samples are cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 500%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Example 6
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-6MA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into preforms of 6X 30X 100mm (for the preparation of impact bars) and 3X 30X 100mm (for the preparation of secondary tensile bars), the molding temperature being 200 ℃ and the pressure 10MPa for a period of 10min, and the samples are cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 700%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Figure 1 shows the stress-strain curve of the example 6 sample during the stretching process. The stress-strain curve can be divided into three different regions according to different stress responses during stretching: an elastically deformable zone (I), a strain-softened zone (II) and a strain-hardened zone (III). The yield point (strain 100%, example 1) is preceded by an elastic deformation zone (I), the sample exhibits hooke elastic behavior, the strain can be recovered by removing the stress, leaving no permanent deformation; the area behind the yield point is a plastic deformation area, and the sample shows plastic behavior; if the stress is removed, the strain cannot be recovered, leaving a permanent set. In the plastic deformation zone, where the strain is in the range of 100% -200%, the stress decreases or remains unchanged with increasing strain, called strain softening zone (II); when the strain is more than 200% (example 2), the stress sharply increases with an increase in strain, which is called a strain hardening zone (III). When the temperature of the stretching chamber is 70 ℃, the originally frozen chain segment in the polylactic acid blending material starts to move, and the extension of the macromolecular chain provides the deformation of the material. When the sample is stretched to a set strain at 70 ℃ and then cooled to room temperature, the stretched polymer chains are frozen again, and even if the external force is removed, the deformation cannot be spontaneously recovered. Therefore, according to the stress-strain curve, different tensile strains are selected in the three different areas, tensile sample bars under corresponding strains are prepared, and mechanical property testing and microstructure characterization are carried out on the tensile sample bars.
FIG. 4 shows that the polylactic acid blend material exhibits significant brittleness at room temperature and a notched impact strength of only 2.6KJ/m when unstretched2. When the polylactic acid blended material is stretched to 100% at 70 ℃ (example 1), the condensed entangled network is just recombined, the orientation degree is low, and the notch impact strength is not obviously changed. When stretched to 200% (example 2), the notched impact strength of the sample increased sharply with further increase in the degree of orientation, from 12KJ/m2(example 1) increase to 204KJ/m2The intensity value is 12KJ/m2Is approximately 17 times of that of the previous one and is 2.6KJ/m278 times higher. With progression of tensile strainThe notch impact strength of the polylactic acid blended material is continuously improved in one step, and when the tensile strain is 400 percent (example 4), the maximum value of the notch impact strength is 272KJ/m2The toughening effect is very obvious, and the notch impact strength value of the unstretched polylactic acid blended material is 2.6KJ/m2105 times higher than the original value. After the notch impact strength of the polylactic acid blend material reaches a maximum value, the oriented fiberized structure inside the sample may be tensile-fractured with further increase of tensile strain, resulting in a decrease in the notch impact strength.
Fig. 5 shows that the stretching behavior of the polylactic acid blend material obtained by the stretching treatment is also changed significantly, and the polylactic acid blend material is transformed from brittle fracture to ductile fracture at room temperature, and shows typical phenomena of yield, thin neck and strain hardening. In addition, the thin neck region of the sample strip subjected to secondary stretching at room temperature gradually becomes smaller as the tensile strain increases; when the tensile strain was increased to 700% (example 6), the neck-in phenomenon almost disappeared.
Fig. 6 shows that the elongation at break of the secondary stretching at room temperature of the polylactic acid blend material obtained by the stretching treatment gradually decreases with the increase of the stretching strain. The polylactic acid blend has a maximum elongation at break (101%) when the tensile strain of the polylactic acid blend is 100% (example 1); when the tensile strain of the polylactic acid blend material was the greatest (example 6), the elongation at break was the smallest (17%), but still greater than the elongation at break of the unstretched unblended polylactic acid bars (6%).
Fig. 7 shows that the breaking strength of the secondary stretching of the polylactic acid blend material obtained by the stretching treatment at room temperature gradually increases with the increase of the stretching strain. When the tensile strain of the polylactic acid blend material was 100% (example 1), the breaking strength of the polylactic acid blend material did not show a significant increase compared to the non-stretched non-blended polylactic acid material. With further increase of tensile strain, the fracture strength of the polylactic acid blend material in secondary stretching at room temperature gradually increases, and when the polylactic acid blend material is stretched to the maximum strain of 700% (example 6), the fracture strength shows the maximum value and is 171 MPa.
FIG. 8 shows the stretching of the polylactic acid blend material obtained by the stretching treatment by the secondary stretching at room temperatureThe toughness gradually decreases with increasing tensile strain. The polylactic acid blend material has the maximum tensile toughness (46 KJ/m) when the tensile strain of the polylactic acid blend material is 100% (example 1)3) (ii) a When the tensile strain of the polylactic acid blend material is maximized (example 6), the tensile toughness is minimized (20 KJ/m)3) But still greater than the tensile toughness (1.8 KJ/m) of the unstretched unblended polylactic acid spline3)。
Fig. 10 shows that after stretching (example 6), the microstructure ordering along the stretching direction is evident, resulting in oriented microstructure.
Example 7
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 80/20, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into preforms of 6X 15X 100mm (for the preparation of impact bars) and 3X 30X 100mm (for the preparation of secondary tensile bars), the molding temperature being 200 ℃ and the pressure 10MPa for a period of 10min, and the samples are cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on temperature-controlled stretching equipment, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 100%, and after the preset strain is reached, cooling and curing are carried out in a room-temperature air environment to obtain the polylactic acid with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Example 8
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 80/20, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into preforms of 6X 18X 100mm (for the preparation of impact bars) and 3X 30X 100mm (for the preparation of secondary tensile bars), the molding temperature being 200 ℃ and the pressure 10MPa for 10min, and the samples are cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 200%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Example 9
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 80/20, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The resulting blend was compression molded in a compression molding machine into 6X 22X 100mm (for making impact bars) and 3X 30X 100mm (for making secondary tensile bars) preforms at 200 ℃ under 10MPa for 10min, and the samples were cooled to room temperature by ice water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 300%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Example 10
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 80/20, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The resulting blend was compression molded in a compression molding machine into preforms of 9X 20X 100mm (for making impact bars) and 3X 30X 100mm (for making secondary tensile bars), at a compression molding temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples were cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 400%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Fig. 20 shows a storage modulus-temperature change curve in a dynamic mechanical analysis test of example 10, and it can be seen that the storage modulus at 106 ℃ is 214MPa, which is much higher than the storage modulus values of comparative example 2(103 ℃, 2.4MPa) and comparative example 3(103 ℃, 3.3MPa) under the same temperature conditions, indicating that the heat resistance of the material is significantly improved by the stretching treatment, and fig. 20 shows that the heat resistance temperature of the bar can be raised to 142 ℃.
Example 11
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 80/20, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into preforms of 6X 30X 100mm (for the preparation of impact bars) and 3X 30X 100mm (for the preparation of secondary tensile bars), the molding temperature being 200 ℃ and the pressure 10MPa for a period of 10min, and the samples are cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 500%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Example 12
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 80/20, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into preforms of 6X 30X 100mm (for the preparation of impact bars) and 3X 30X 100mm (for the preparation of secondary tensile bars), the molding temperature being 200 ℃ and the pressure 10MPa for a period of 10min, and the samples are cooled to room temperature by ice-water quenching. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 700%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Figure 14 shows the stress-strain curve of the example 12 sample during the stretching process. The stress-strain curve can be divided into three different regions according to different stress responses during stretching: an elastically deformable zone (I), a strain-softened zone (II) and a strain-hardened zone (III). The yield point (100% strain, example 7) is preceded by an elastic deformation zone (I), the sample exhibits hooke elastic behavior, the strain can be recovered by removing the stress, leaving no permanent deformation; the area behind the yield point is a plastic deformation area, and the sample shows plastic behavior; if the stress is removed, the strain cannot be recovered, leaving a permanent set. In the plastic deformation zone, where the strain is in the range of 100% -200%, the stress decreases or remains unchanged with increasing strain, called strain softening zone (II); when the strain is more than 200% (example 8), the stress sharply increases with an increase in strain, which is called a strain hardening zone (III). When the polylactic acid blended material is stretched at 70 ℃, the originally frozen chain segment in the polylactic acid blended material starts to move, and the extension of the high molecular chain provides the deformation of the material. When the sample is stretched to a set strain at 70 ℃ and then cooled to room temperature, the stretched polymer chains are frozen again, and even if the external force is removed, the deformation cannot be spontaneously recovered. Therefore, according to the stress-strain curve, different tensile strains are selected in the three different areas, so that tensile sample strips under corresponding strains can be prepared, and the mechanical property test and the microstructure characterization are carried out on the tensile sample strips.
Fig. 15 shows that the polylactic acid blend material obtained after the stretching treatment of example 10 has a milky white color.
FIG. 16 shows that the polylactic acid blend material exhibits brittleness at room temperature and has a notched impact strength of only 21KJ/m when unstretched2. When the polylactic acid blended material is stretched to 100% at 70 ℃ (example 7), the condensation entanglement network is recombined, the sample is oriented, and the notch impact strength is greatly improved to 115KJ/m2. With further increase of tensile strain, the orientation degree of the polylactic acid blended material is increased, the notch impact strength is continuously improved, and when the tensile strain is 400% (example 10), the notch impact strength has a maximum value of 165KJ/m2The toughening effect is very obvious. After the notch impact strength of the polylactic acid blended material reaches the maximum value, the oriented fiberized microstructure in the sample is broken by stretching along with the further increase of the stretching strain, and the notch impact strength is reduced.
Fig. 17 shows that the stretching behavior of the polylactic acid blend material obtained by stretching at 70 ℃ is also changed remarkably, and the polylactic acid blend material is transformed from brittle fracture to ductile fracture at room temperature and shows typical phenomena of yield, thin neck and strain hardening. Furthermore, the narrow neck region of the sample strip twice stretched at room temperature gradually becomes smaller as the tensile strain increases; when the tensile strain was increased to 700% (example 12), the neck-in phenomenon almost disappeared.
Fig. 18 shows that the elongation at break of the secondary stretching at room temperature of the polylactic acid blend material obtained by stretching at 70 ℃ gradually decreases with increasing tensile strain. The polylactic acid blend has a maximum elongation at break (124%) when the tensile strain of the polylactic acid blend is 100% (example 7); when the tensile strain of the polylactic acid blend material is the greatest (example 12), the elongation at break is the smallest (20%), but still greater than the elongation at break of the un-stretched unblended polylactic acid material (6%).
Fig. 19 shows that the breaking strength of the secondary stretching at room temperature of the polylactic acid blend material obtained by stretching at 70 ℃ gradually increases with the increase of the tensile strain. When the tensile strain of the polylactic acid blend material was 100% (example 7), the breaking strength of the polylactic acid blend material did not show a significant increase compared to the unstretched polylactic acid material. With further increase of tensile strain, the fracture strength of the polylactic acid blend material in secondary stretching at room temperature gradually increases, and when the polylactic acid blend material is stretched to the maximum strain of 700% (example 12), the fracture strength has the maximum value of 144 MPa.
Example 13
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 80/20, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into 9X 20X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 80 ℃, the stretching speed is 20mm/min, the strain is 400%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 129KJ/m2。
Example 14
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 99/1, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into 9X 20X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 400%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 203KJ/m2。
Example 15
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-6MA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into 6X 22X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 50mm/min, the strain is 300%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 222KJ/m2。
Fig. 23 shows that the polylactic acid material thus obtained after the stretching treatment at 70 ℃ takes a translucent shape.
Example 16
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into 6X 22X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 1mm/min, the strain is 300%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 156KJ/m2。
Fig. 24 shows that the polylactic acid material thus obtained after the stretching treatment at 70 ℃ takes a translucent shape.
Example 17
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into 6X 22X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Mash corporation in temperature-controlled stretching equipment, wherein the temperature of a stretching chamber is 90 ℃, the stretching speed is 20mm/min, the strain is 300%, and after the preset strain is reached, cooling and curing are carried out in a room-temperature air environment to obtain a polylactic acid sample with the tensile strain of 300%. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 6KJ/m2。
Fig. 25 shows that the polylactic acid material thus obtained after the stretching treatment at 90 ℃ takes a translucent shape.
Example 18
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into 6X 22X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 60 ℃, the stretching speed is 20mm/min, the strain is 300%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 229KJ/m2。
Fig. 26 shows that the polylactic acid material thus obtained after the stretching treatment at 60 ℃ takes a translucent shape.
Example 19
And (2) banburying the polylactic acid and the natural rubber which are dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the banburying temperature is 200 ℃, the rotating speed is 80rpm, and the banburying time is 12 min. The blend obtained is molded in a molding press into 6X 22X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 300%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 152KJ/m2。
Fig. 27 shows that the polylactic acid material thus obtained after the stretching treatment at 70 ℃ exhibits a light milky yellow color.
Example 20
Mixing polylactic acid and hydrogenated polystyrene-polybutadiene-polystyrene triblock copolymer (SEBS) which are dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into 6X 22X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 300%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 195KJ/m2。
Fig. 28 shows that the polylactic acid material thus obtained after the stretching treatment at 70 ℃ exhibits a light milky yellow color.
Example 21
Mixing polylactic acid and Polycaprolactone (PCL) dried for 12 hours at 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. The blend obtained is molded in a molding press into 6X 22X 100mm (for the preparation of impact bars) preforms at a temperature of 200 ℃ and a pressure of 10MPa for a period of 10min, and the samples are cooled to room temperature by quenching with ice water. And (2) stretching the parison on a UTM2502 universal testing machine of Shenzhen Sansi company on a temperature-controlled stretching device, wherein the temperature of a stretching chamber is 70 ℃, the stretching speed is 20mm/min, the strain is 300%, and after the preset strain is reached, cooling and solidifying are carried out in a room-temperature air environment to obtain the polylactic acid sample with ultrahigh impact strength. The samples after the stretching treatment were cut to prepare rectangular impact specimens of 3X 80X 10mm with notches, and then subjected to an impact test.
The notch impact strength of the polylactic acid material sample is 181KJ/m2。
Fig. 29 shows that the polylactic acid material thus obtained after the stretching treatment at 70 ℃ is translucent.
Comparative example 1
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 95/5, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. And (3) molding the obtained blend into a polylactic acid sheet in a molding press, wherein the molding temperature is 200 ℃, the pressure is 10MPa, and the time is 10min, and cooling the sample to room temperature by ice water quenching. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
Comparative example 2
Mixing polylactic acid and ethylene-methyl acrylate-glycidyl methacrylate random copolymer (EMA-GMA) (the number average molecular weight is 130k) dried for 12 hours at the temperature of 60 ℃ in a torque rheometer according to the mass part ratio of 80/20, wherein the mixing temperature is 200 ℃, the rotating speed is 80rpm, and the mixing time is 12 min. And (3) molding the obtained blend into a polylactic acid sheet in a molding press, wherein the molding temperature is 200 ℃, the pressure is 10MPa, and the time is 10min, and cooling the sample to room temperature by ice water quenching. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
FIG. 21 shows the storage modulus-temperature change curve of the dynamic mechanical analysis test of comparative example 2, which has a storage modulus of only 14MPa at 80 ℃ and a storage modulus much lower than that of example 10(1054MPa) under the same temperature conditions, indicating that the sample of example 10 has a significantly increased heat-resistant temperature due to the stretching treatment.
Comparative example 3
And (3) molding the polylactic acid dried for 12 hours at the temperature of 60 ℃ into a polylactic acid sheet in a molding press, wherein the molding temperature is 200 ℃, the pressure is 10MPa, and the time is 10min, and cooling the sample to room temperature by ice water quenching. The tensile-treated samples were cut to prepare 3X 80X 10mm notched rectangular impact bars and 1X 4X 50mm dumbbell-shaped tensile bars, which were then subjected to impact and tensile tests, respectively.
FIG. 22 shows a graph of storage modulus versus temperature change in the dynamic mechanical analysis test of comparative example 3, with a storage modulus of 23MPa at 80 ℃ which is much lower than that of example 10(1054MPa) under the same temperature conditions, indicating that the sample of example 10 significantly increases the heat-resistant temperature of the material due to the stretching treatment.
As can be seen from the above examples and the accompanying FIGS. 1 to 19, the polylactic acid blend material subjected to the drawing process at a temperature not lower than the glass transition temperature of each system has a breaking strength of 60MPa to 171MPa, an elongation at break of 6% to 17-124%, and a notched impact strength of 2KJ/m2Increased to 272KJ/m2The reinforcing and toughening effects obtained are very significant. The stretching treatment can also increase the crystallinity of the polylactic acid matrix, thereby greatly improving the heat resistance of the material.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A preparation method of a polylactic acid material with ultrahigh impact strength comprises the following steps:
(1) blending the polylactic acid granules and the toughening agent in a polylactic acid molten state;
(2) forming the blend to obtain a parison;
(3) and stretching the parison above the glass transition temperature of the parison, and then cooling and solidifying the parison below the glass transition temperature of the parison, thereby obtaining the polylactic acid material with ultrahigh impact strength.
2. The method for preparing polylactic acid material with ultrahigh impact strength according to claim 1, wherein the toughening agent is elastomer or plastic.
3. The method of preparing an ultra-high impact strength polylactic acid material according to claim 1, wherein the toughening agent is selected from the group consisting of ethylene-methyl acrylate-glycidyl methacrylate random copolymer, hydrogenated polystyrene-polybutadiene-polystyrene triblock copolymer, natural rubber and polycaprolactone plastic.
4. The method for preparing a polylactic acid material with ultra-high impact strength according to claim 1, wherein in the step (1):
the mass ratio of the toughening agent to the polylactic acid granules is 1: 1-99.
5. The method for preparing a polylactic acid material with ultra-high impact strength according to claim 1, wherein in the step (1):
the blending temperature is 160-250 ℃, and the blending time is 3-30 min.
6. The method for preparing a polylactic acid material with ultra-high impact strength according to claim 1, wherein in the step (3):
the temperature of the stretching treatment is between the glass transition temperature of the polylactic acid blend and 90 ℃.
7. The method for preparing a polylactic acid material with ultra-high impact strength according to claim 1, wherein in the step (3):
in the stretching process, the stretching rate is 1 to 50 mm/min.
8. The method for preparing a polylactic acid material with ultra-high impact strength according to claim 1, wherein in the step (3):
during the stretching treatment, the stretching strain is 100-700%.
9. Super highAn impact strength polylactic acid material comprising 80 to 99% by mass of polylactic acid and 1 to 20% by mass of a toughening agent, and having a breaking strength of at most 171MPa, an elongation at break of 17 to 124%, at most 272KJ/m2Notched impact strength of (2).
10. The ultra-high impact strength polylactic acid material of claim 9, which is a biodegradable plastic.
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