CN109648881B - Transparent polylactic acid film and preparation method and application thereof - Google Patents
Transparent polylactic acid film and preparation method and application thereof Download PDFInfo
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- CN109648881B CN109648881B CN201811554766.9A CN201811554766A CN109648881B CN 109648881 B CN109648881 B CN 109648881B CN 201811554766 A CN201811554766 A CN 201811554766A CN 109648881 B CN109648881 B CN 109648881B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
- B29K2067/04—Polyesters derived from hydroxycarboxylic acids
- B29K2067/046—PLA, i.e. polylactic acid or polylactide
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
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- B29L2007/00—Flat articles, e.g. films or sheets
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Abstract
The invention belongs to the technical field of high polymer materials and biomedical materials, and particularly relates to a transparent polylactic acid film and a preparation method and application thereof. The invention provides a preparation method of a transparent polylactic acid film, which comprises the following steps: melting polylactic acid in an extruder to obtain a melt, extruding the melt by the extruder, cooling by an air knife, stretching by a casting roll, drawing by a traction roll, and forming a film by winding to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the extruder is 150-210 ℃, and the ratio of the melt at the extrusion opening film speed to the linear speed of the casting roll is 1: (30-160), the air knife is arranged between the extrusion port film and the casting roller, and the included angle formed by the air port direction of the air knife and the surface of the melt is 45-90 degrees. The preparation method can prepare the transparent polylactic acid film without adding any filler auxiliary agent, the transparent polylactic acid film has oriented fiber crystals and/or an oriented structure as a whole, and the film has high elongation at break and tensile strength even if the crystallinity is lower than 8 percent.
Description
Technical Field
The invention belongs to the technical field of high polymer materials and biomedical materials, and particularly relates to a transparent polylactic acid film and a preparation method and application thereof.
Background
The polylactic acid is obtained by lactic acid polycondensation or lactide ring-opening polymerization, the synthetic raw materials of the polylactic acid are from crops such as corn stalks, potatoes and the like, and can be degraded under natural conditions, compared with the traditional plastics, the polylactic acid is renewable, the polylactic acid is rich in reserves and low in price, and belongs to environment-friendly materials. Has good biocompatibility, can be absorbed by human body, and can be applied to medical materials such as bone nails, sutures and the like. Although polylactic acid has considerable application prospect, the poor toughness (the elongation at break is only 6%) severely limits the application range of the polylactic acid.
Disclosure of Invention
In view of the above, the invention provides a transparent polylactic acid film, and a preparation method and an application thereof, which are used for solving the problem of poor toughness of the existing transparent polylactic acid film.
The specific technical scheme of the invention is as follows:
a preparation method of a transparent polylactic acid film comprises the following steps:
melting polylactic acid in an extruder to obtain a melt, extruding the melt by the extruder, cooling by an air knife, stretching by a casting roll, drawing by a traction roll, and forming a film by winding to obtain a transparent polylactic acid film;
wherein the temperature of an extrusion opening film of the extruder is 150-210 ℃, and the ratio of the melt to the linear speed of the casting roller at the extrusion opening film is 1: (30-160), the air knife is arranged between the extrusion port film and the casting roller, and the included angle formed by the air port direction of the air knife and the surface of the melt is 45-90 degrees.
In the present invention, the temperature of the extrusion port film is preferably 190 to 210 ℃, and the ratio of the melt at the extrusion port film speed to the casting roll linear speed is preferably 1: (40-120). The preparation method of the transparent polylactic acid film only adopts polylactic acid as a raw material and does not add any processing aid.
Preferably, the air blowing quantity of the air knife is 50m3/min～250m3/min；
The blast temperature of the air knife is 0-100 ℃.
In the present invention, the cooling mode of the air knife is roller cooling, and the blowing temperature of the air knife is preferably 0 ℃ to 80 ℃.
Preferably, the distance between the extrusion port film and the casting roller is 100 mm-300 mm;
the roll temperature of the casting roll is 0-100 ℃.
In the present invention, the distance between the extrusion port film and the casting roll is preferably 150mm to 250mm, and the roll temperature of the casting roll is preferably 0 ℃ to 80 ℃.
Preferably, the melt index of the polylactic acid is 6g/10 min-15 g/10min, and the test condition is that a 2.16kg load test is adopted at 190 ℃;
the number average molecular weight of the polylactic acid is 100 kg/mol-210 kg/mol, the molecular weight distribution of the polylactic acid is 1.1-2.4, and the levorotatory content of the polylactic acid is 95% -99%.
Preferably, the water content of the polylactic acid is 0-0.001%;
the particle size of the polylactic acid is 2-5 mm.
In the present invention, before the polylactic acid is melted in an extruder to obtain a melt and extruded by the extruder, the method further comprises: drying the polylactic acid at 60-80 ℃ for 8-12 h.
In the present invention, polylactic acid is purchased from Nature works, USA, and preferably is one or more of PLA-2002D polylactic acid, PLA-2003D polylactic acid, PLA-4032D polylactic acid, PLA-4043D polylactic acid and PLA-7032 polylactic acid. Different types of polylactic acid are mixed, the molecular weight distribution and the melt index can be regulated and controlled, and then transparent polylactic acid films with different structural parameters are obtained.
In the present invention, the temperature of the extruder is preferably set to 150 ℃ (feed zone) -170 ℃ -175 ℃ -180 ℃ -190 ℃ (barrel zone) -200 ℃ -210 ℃ (transition zone) -190 ℃ (oral membrane zone)
The invention also provides the transparent polylactic acid film prepared by the preparation method of the technical scheme.
Preferably, the elongation at break of the transparent polylactic acid film is 150-280%;
the crystallinity of the transparent polylactic acid film is 0-8%.
In the invention, the transparent polylactic acid film has the tensile strength as high as 220MPa when measured under the test standard of ASTM-D882.
In the invention, the transparent polylactic acid film has high orientation degree, and the amorphous region wraps the oriented fiber, so that the orientation of the transparent polylactic acid film can be regulated and controlled.
Preferably, the transparent polylactic acid film has oriented fiber crystals along the casting or rolling direction, the diameter of the fiber crystals is 80 nm-1500 nm (for the simplicity and clarity of expression, the structure is called as 'A structure', the diameter of the fiber crystals is dA)，
And/or the transparent polylactic acid film is integrally of an oriented structure, the width of the oriented structure is 2 mu m to E60 μm (for simplicity and clarity, the structure is referred to as "B structure" and the width of the oriented structure is W)B)。
Preferably, the orientation structure is a Shish-like-Kebab structure, the transverse dimension of the orientation structure is 80nm to 1000nm, and the longitudinal dimension of the orientation structure is 0nm to 1500nm (for simplicity and clarity, the transverse dimension of the orientation structure is XBThe longitudinal dimension of the oriented structure is YB)。
In the invention, the transparent polylactic acid film is a high-transparency film, and the thickness of the transparent polylactic acid film is 8-50 μm.
The preparation method of the invention adopts a melt extrusion casting process or a calendering process, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 45-90 degrees, the transparent polylactic acid film with an oriented structure, low crystallinity, ultrahigh breaking elongation and biodegradability can be prepared, the structure of the transparent polylactic acid film is oriented fiber with an amorphous region wrapping structure controllable, no filler auxiliary agent is added, the crystallinity is lower than 8 percent, and the transparent polylactic acid film also has very high breaking elongation and tensile strength, and has excellent transparency, biocompatibility and degradability.
The transparent polylactic acid film has high orientation, low crystallinity and excellent mechanical property, has biocompatibility and biodegradability, and has the mass loss up to 36.7 percent, the number average molecular weight is reduced to 55kg/mol, and the weight average molecular weight is reduced to 180kg/mol through a degradation performance test for 180 days.
The invention also provides the transparent polylactic acid film prepared by the preparation method of the technical scheme or the application of the transparent polylactic acid film in medical materials.
The transparent polylactic acid film is not added with any filler auxiliary agent, has excellent transparency, ensures the biocompatibility of polylactic acid, is non-toxic and harmless, has ultrahigh breaking elongation and tensile strength, has the characteristics of transparency, good hand feeling, biodegradation, compatibility and the like, and can be applied to the fields of high polymer materials and biomedical materials.
In summary, the invention provides a preparation method of a transparent polylactic acid film, which comprises the following steps: melting polylactic acid in an extruder to obtain a melt, extruding the melt by the extruder, cooling by an air knife, stretching by a casting roll, drawing by a traction roll, and forming a film by winding to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the extruder is 150-210 ℃, and the ratio of the melt to the linear speed of the casting roller at the extrusion opening film is 1: (30-160), the air knife is arranged between the extrusion port film and the casting roller, and the included angle formed by the air port direction of the air knife and the surface of the melt is 45-90 degrees. The preparation method of the transparent polylactic acid film has the advantages of simple preparation process, high production efficiency and capability of realizing large-scale production, and experimental results show that the preparation method of the transparent polylactic acid film can prepare the transparent polylactic acid film without adding any filler auxiliary agent, oriented fiber crystals exist in the transparent polylactic acid film and/or the transparent polylactic acid film is in an oriented structure as a whole, the crystallinity is lower than 8%, the transparent polylactic acid film also has high elongation at break and tensile strength, and the transparent polylactic acid film has excellent transparency, biocompatibility and degradability.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
FIG. 1 is a schematic structural diagram of the structure A in the transparent polylactic acid film according to the embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a structure B in the transparent polylactic acid film according to the embodiment of the present invention;
FIG. 3 is a scanning electron micrograph of a transparent polylactic acid film obtained in example 1 according to the present invention;
FIG. 4 is a scanning electron micrograph of a transparent polylactic acid film obtained in example 2 according to the present invention;
FIG. 5 is a scanning electron micrograph of a transparent polylactic acid film obtained in example 3 according to the present invention;
FIG. 6 is a scanning electron micrograph of a transparent polylactic acid film obtained in example 4 according to the present invention;
FIG. 7 is a scanning electron micrograph of a transparent polylactic acid film obtained in example 5 according to the present invention;
FIG. 8 is a scanning electron micrograph of a transparent polylactic acid film obtained in example 6 according to the present invention;
FIG. 9 is a scanning electron micrograph of a transparent polylactic acid film according to comparative example 1 of the present invention;
FIG. 10 is a graph showing the mechanical properties of a transparent polylactic acid film obtained by using a melt of an embodiment of the present invention at different speed ratios of a screw extrusion port film speed and a casting roll linear speed.
Detailed Description
The invention provides a transparent polylactic acid film, a preparation method and application thereof, which are used for solving the problem of poor toughness of the existing transparent polylactic acid film.
Please refer to fig. 1 and fig. 2 for the structural schematic diagrams of the structure a and the structure B in the transparent polylactic acid film according to the embodiment of the present invention.
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
In the embodiment, dried PLA-2003D polylactic acid with a melt index of 7.8g/10min is placed into a screw extruder when the temperature of the screw extruder reaches a preset temperature, waiting for 3-5 min, starting a device (air removal knife), melting the PLA-2003D polylactic acid, starting the air knife when a melt is extruded stably by the screw extruder, cooling the melt by the air knife, stretching by a casting roll, drawing by a drawing roll, and winding to form a film to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and the ratio of the melt at the screw extrusion opening film speed to the casting roll linear speed is 1: 40, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 150m3Min, the blast temperature of an air knife is 10 ℃, and the roller temperature of a casting roller is 60 DEG C。
FIG. 3 is a scanning electron microscope image of the transparent polylactic acid film obtained in example 1 of the present invention. The thickness of the transparent polylactic acid film prepared in the embodiment is 40 +/-2 mu m, the film is of an A structure, and dAThe amorphous area is dominant between 80nm and 500nm, and the crystallinity of the transparent polylactic acid film is 0 to 2 percent.
Example 2
In the embodiment, dried PLA-2003D polylactic acid with a melt index of 7.8g/10min is placed into a screw extruder when the temperature of the screw extruder reaches a preset temperature, waiting for 3-5 min, starting a device (air removal knife), melting the PLA-2003D polylactic acid, starting the air knife when a melt is extruded stably by the screw extruder, cooling the melt by the air knife, stretching by a casting roll, drawing by a drawing roll, and winding to form a film to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and the ratio of the melt at the screw extrusion opening film speed to the casting roll linear speed is 1: 120, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 150m3Min, the blowing temperature of an air knife is 10 ℃, and the roll temperature of a casting roll is 60 ℃.
FIG. 4 is a scanning electron microscope image of the transparent polylactic acid film obtained in example 2 of the present invention. The thickness of the transparent polylactic acid film prepared in the embodiment is 8 +/-2 mu m, the film is of an A structure, and dAThe fiber crystals are densely arranged between 100nm and 1500nm, and the crystallinity of the transparent polylactic acid film is 3 percent to 5 percent.
Example 3
In the embodiment, dried PLA-4043D polylactic acid with a melt index of 8g/10min is put into a screw extruder when the temperature of the screw extruder reaches a preset temperature, waiting for 3-5 min, starting a device (an air removal knife), melting the PLA-4043D polylactic acid, starting the air removal knife when a melt is extruded stably by the screw extruder, cooling the melt by the air removal knife, stretching by a casting roll, drawing by a drawing roll, and forming a film by winding to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and a melt is extruded in the screw extruderThe ratio of exit film speed to casting roll linear speed was 1: 40, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 150m3Min, the blowing temperature of an air knife is 10 ℃, and the roll temperature of a casting roll is 60 ℃.
FIG. 5 is a scanning electron microscope image of the transparent polylactic acid film obtained in example 3 of the present invention. The thickness of the transparent polylactic acid film prepared in the embodiment is 35 +/-2 mu m, the film is of a B structure, and W isB2 to 20 μm, XBIs 400 to 500nm, YB80-1500 nm, and the crystallinity of the transparent polylactic acid film is 1-3%.
Example 4
In the embodiment, dried PLA-4043D polylactic acid with a melt index of 8g/10min is put into a screw extruder when the temperature of the screw extruder reaches a preset temperature, waiting for 3-5 min, starting a device (an air removal knife), melting the PLA-4043D polylactic acid, starting the air removal knife when a melt is extruded stably by the screw extruder, cooling the melt by the air removal knife, stretching by a casting roll, drawing by a drawing roll, and forming a film by winding to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and the ratio of the melt at the screw extrusion opening film speed to the casting roll linear speed is 1: 120, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 150m3Min, the blowing temperature of an air knife is 10 ℃, and the roll temperature of a casting roll is 60 ℃.
FIG. 6 is a scanning electron microscope image of a transparent polylactic acid film obtained in example 4 of the present invention. The thickness of the transparent polylactic acid film prepared in the embodiment is 7 +/-2 mu m, the film is of a B structure, and W isB2 to 60 μm, XB500-1000 nm, basically no Shish structure, and the crystallinity of the transparent polylactic acid film is 5-8%.
Example 5
This example blends the oven dried PLA-2003D polylactic acid and PLA-4043D polylactic acid with a melt index of 7.9g/10min (PLA-2003D)The mass ratio of polylactic acid to PLA-4043D polylactic acid is 1:1), when the temperature of a screw extruder reaches a preset temperature, putting the polylactic acid into the screw extruder, waiting for 3-5 min, starting a device (an air removal knife), melting the polylactic acid, starting the air removal knife when a melt is extruded stably by the screw extruder, cooling the melt by the air removal knife, stretching the melt by a casting roll, drawing by a drawing roll, and forming a film by winding to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and the ratio of the melt at the screw extrusion opening film speed to the casting roll linear speed is 1: 40, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 150m3Min, the blowing temperature of an air knife is 10 ℃, and the roll temperature of a casting roll is 60 ℃.
FIG. 7 is a scanning electron microscope image of a transparent polylactic acid film obtained in example 5 of the present invention. The thickness of the transparent polylactic acid film prepared in the example is 35 +/-2 microns, the film is a mixed structure of an A structure and a B structure, and dABetween 80nm and 500nm, WB2 to 20 μm, XBIs 400 to 500nm, YB80-2000 nm, and the crystallinity of the transparent polylactic acid film is 3.3%.
Example 6
In the embodiment, a dried mixture of PLA-2003D polylactic acid and PLA-4043D polylactic acid with a melt index of 7.9g/10min (the mass ratio of the PLA-2003D polylactic acid to the PLA-4043D polylactic acid is 1:1) is placed into a screw extruder when the temperature of the screw extruder reaches a preset temperature, the screw extruder is waited for 3-5 min, a device (an air removing knife) is started, the polylactic acid is melted, an air knife is started when a melt is extruded out stably by the screw extruder, the melt is cooled by the air knife, stretched by a casting roll, pulled by a pulling roll, and wound to form a film, so that a transparent polylactic acid film is obtained; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and the ratio of the melt at the screw extrusion opening film speed to the casting roll linear speed is 1: 120, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 150m3Min, blast temperature of air knife isThe roll temperature of the casting roll was 60 ℃ at 10 ℃.
FIG. 8 is a scanning electron microscope image of the transparent PLA film obtained in example 6 of the present invention. The thickness of the transparent polylactic acid film prepared in the example is 8 +/-2 microns, the film is a mixed structure of an A structure and a B structure, and dABetween 100nm and 1500nm, WB2 to 60 μm, XB500-1000 nm, basically no Shish structure, and the crystallinity of the transparent polylactic acid film is 7.8%.
Comparative example 1
According to the comparative example, dried PLA-2003D polylactic acid with the melt index of 7.8g/10min is placed into a screw extruder when the temperature of the screw extruder reaches a preset temperature, waiting for 3-5 min, starting a device (air removing knife), melting the PLA-2003D polylactic acid, starting the air knife when a melt is extruded stably by the screw extruder, cooling the melt by the air knife, stretching by a casting roll, drawing by a drawing roll, and winding to form a film to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and the ratio of the melt at the screw extrusion opening film speed to the casting roll linear speed is 1:10, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 80m3Min, the blowing temperature of an air knife is 30 ℃, and the roll temperature of a casting roll is 60 ℃.
FIG. 9 is a scanning electron micrograph of a transparent polylactic acid film according to comparative example 1 of the present invention. The transparent polylactic acid film prepared by the comparative example has a mosaic structure and is not oriented.
Comparative example 2
According to the comparative example, dried PLA-4043D polylactic acid with the melt index of 8g/10min is placed into a screw extruder when the temperature of the screw extruder reaches a preset temperature, waiting for 3-5 min, starting a device (air removal knife), melting the PLA-4043D polylactic acid, starting the air knife when a melt is extruded stably by the screw extruder, cooling the melt by the air knife, stretching by a casting roll, drawing by a drawing roll, and forming a film by winding to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and a melt is extruded out of the screwThe ratio of the speed of the film to the linear speed of the casting roll is 1:10, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 80m3Min, the blowing temperature of an air knife is 30 ℃, and the roll temperature of a casting roll is 60 ℃.
The transparent polylactic acid film prepared by the comparative example has a mosaic structure and is not oriented.
Comparative example 3
According to the comparative example, a dried mixture of PLA-2003D polylactic acid and PLA-4043D polylactic acid with a melt index of 7.9g/10min (the mass ratio of the PLA-2003D polylactic acid to the PLA-4043D polylactic acid is 1:1) is placed into a screw extruder when the temperature of the screw extruder reaches a preset temperature, a device (an air knife) is started for 3-5 min, the polylactic acid is melted, an air knife is started when a melt is extruded out stably by the screw extruder, the melt is cooled by the air knife, stretched by a casting roll, pulled by a traction roll, and formed into a film and wound to obtain a transparent polylactic acid film; wherein the temperature of an extrusion opening film of the screw extruder is 190-210 ℃, and the ratio of the melt at the screw extrusion opening film speed to the casting roll linear speed is 1:10, the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 75 degrees, the distance between the extrusion port film and the casting roller is 150mm, and the blowing amount of the air knife is 80m3Min, the blowing temperature of an air knife is 30 ℃, and the roll temperature of a casting roll is 60 ℃.
The transparent polylactic acid film prepared by the comparative example has a mosaic structure and is not oriented.
Comparative example 4
Drying the levorotatory polylactic resin with the molecular weight of 150Kg/mol, adding the dried levorotatory polylactic resin into an extrusion casting machine, setting the die head temperature at 175 ℃, and the cooling air volume at 40m3The cooling air volume is 40 ℃, the casting roller temperature is 50 ℃, the cooling roller temperature is-20 ℃, the first stage is melt stretching, the ratio of the extrusion speed of the neck ring mold to the linear speed of the casting roller is 1:5, the second stage is solid phase stretching, the ratio of the linear speed of the casting roller to the linear speed of the cooling roller is 1: 5.2, obtaining a transparent polylactic acid film with high crystallinity and mutually vertical crystal structures after traction and winding。
Example 8
In this example, the transparent polylactic acid films of examples 1 to 6 and the transparent polylactic acid films of comparative examples 1 to 4 were examined for physical properties. The results are shown in table 1, and compared with comparative examples 1 to 4, the transparent polylactic acid films of examples 1 to 6 have high elongation at break, modulus and strength, low haze and strong light transmittance.
TABLE 1 physical Properties and crystallinities of transparent polylactic acid films of examples 1 to 6 and comparative examples 1 to 4
Note: in the stretching process, the thickness of the transparent polylactic acid film is changed, and the thickness of the polylactic acid film is changed to be half of the original thickness near the fracture.
Example 9
In the embodiment, the transparent polylactic acid films of the examples 1 to 6 and the transparent polylactic acid films of the comparative examples 1 to 4 are subjected to degradation performance detection. The detection method comprises the following steps:
mixing garden soil and tap water according to the mass ratio of 1:10, stirring for 2 hours, and performing centrifugal filtration to obtain a supernatant for later use. Accurately weighed degradation sample strips (degradation sample strip preparation: cutting a transparent polylactic acid film into 20mm x100mm by using a cutter) were placed in the supernatant obtained in the previous step. After a period of time, the degraded specimen is removed and washed, dried to constant weight under vacuum (30 ℃) and weighed. Taking 3 parallel samples in each group, calculating the average value, solving the performance calculation formula by the reference example 1: m isloss＝(m0-mt)/m0X 100%. In the formula: m islossMass loss rate; m is0And mt is the mass of the degraded sample strip before and after degradation. The experimental results are shown in Table 2, and the results show that the loss rate of the transparent polylactic acid films of the examples 1-6 is basically higher than 25%, and the transparent polylactic acid films have excellent performanceDifferent degradation properties.
The molecular weights of the degraded specimen before and after degradation were measured, and the number average molecular weight and the weight average molecular weight (Mn and Mw, respectively) of the degraded specimen were measured by gel permeation chromatography. Wherein chloroform is used as eluent (flow rate is 1mL/min), the concentration of the filtered sample is 1-2 mg/mL, the injection amount is 10 mu L, the column temperature is 40 ℃, and the standard sample is polystyrene. The experimental results are shown in table 3, and the results show that compared with comparative examples 1 to 4, the molecular weight of the transparent polylactic acid films of examples 1 to 6 after degradation is more obviously reduced, and the molecular chains of the transparent polylactic acid films of examples 1 to 6 are more easily damaged and have more excellent degradation performance.
TABLE 2 Mass loss rates of the transparent polylactic acid films of examples 1 to 6 and the transparent polylactic acid films of comparative examples 1 to 4 at different degradation times
TABLE 3 molecular weights of transparent polylactic acid films of examples 1 to 6 and transparent polylactic acid films of comparative examples 1 to 4 at different degradation times
Note: after degradation represents the sample after 180 days.
Examples 1-6 were compared to comparative example 4, in comparative example 4 a two-step process was used: the high-crystallinity transparent polylactic acid film with mutually vertical crystal structures is prepared by melt stretching and solid-phase stretching, although the elongation at break is improved, the tensile strength and the degradation performance are poor. And in the embodiments 1-6, a one-step method is used, and the transparent polylactic acid film with low crystallinity, a large amount of oriented structures, high mechanical strength and excellent degradation performance is prepared by regulating the blowing direction of an air knife, the blowing temperature, the temperature of a casting roll and the rotating speed, and the film has high elongation at break and tensile strength even if the crystallinity is lower than 8%.
Example 10
In this example, a transparent polylactic acid film was prepared by the same method as in example 1, but the ratio of the film speed at the screw extrusion port to the linear speed of the casting roll in this example was 1: 40. 1: 60. 1: 80, 1: 100 and 1: 120, the mechanical properties of the obtained transparent polylactic acid film are shown in fig. 10, and the results show that the elongation at break of the cast polylactic acid film decreases with the increase of the draw ratio (but the elongation at break at the lowest draw ratio also reaches 150%), and the tensile strength and the breaking strength are improved. The transparent polylactic acid film prepared by the method can strengthen and toughen the transparent polylactic acid film.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (6)
1. A preparation method of a transparent polylactic acid film is characterized by comprising the following steps:
melting polylactic acid in an extruder to obtain a melt, extruding the melt by the extruder, cooling by an air knife, stretching by a casting roll, drawing by a traction roll, and forming a film by winding to obtain a transparent polylactic acid film;
wherein the temperature of an extrusion opening film of the extruder is 150-210 ℃, and the ratio of the melt to the linear speed of the casting roller at the extrusion opening film is 1: (30-160), the air knife is arranged between the extrusion port film and the casting roller, the included angle formed by the air port direction of the air knife and the surface of the melt is 45-90 degrees, and the blowing amount of the air knife is 50m3/min～250m3The blowing temperature of the air knife is 0-100 ℃, the distance between the extrusion opening film and the casting roll is 100-300 mm, and the roll temperature of the casting roll is 0-100 ℃;
the transparent polylactic acid film has oriented fiber crystals along the casting or rolling direction, the diameter of the fiber crystals is 80 nm-1500 nm,
and/or the whole transparent polylactic acid film is an oriented structure, and the width of the oriented structure is 2-60 mu m.
2. The preparation method according to claim 1, wherein the melt index of the polylactic acid is 6g/10min to 15g/10min, and the test condition is that a 2.16kg load test is adopted at 190 ℃;
the number average molecular weight of the polylactic acid is 100 kg/mol-210 kg/mol, the molecular weight distribution of the polylactic acid is 1.1-2.4, and the levorotatory content of the polylactic acid is 95% -99%.
3. The method according to claim 1, wherein the polylactic acid has a water content of 0% to 0.001%;
the particle size of the polylactic acid is 2-5 mm.
4. The preparation method according to claim 1, wherein the elongation at break of the transparent polylactic acid film is 150% to 280%;
the crystallinity of the transparent polylactic acid film is 0-8%.
5. The preparation method according to claim 1, wherein the orientation structure is a Shish-Kebab-like structure, the lateral dimension of the orientation structure is 80nm to 1000nm, and the longitudinal dimension of the orientation structure is 0nm to 1500 nm.
6. Use of the transparent polylactic acid film prepared by the preparation method of any one of claims 1 to 5 in medical materials.
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| CN110845833A (en) * | 2019-11-19 | 2020-02-28 | 广东工业大学 | Polylactic acid film and preparation method thereof |
| CN112280264A (en) * | 2020-10-26 | 2021-01-29 | 厦门长塑实业有限公司 | Master batch for polylactic acid film, preparation method and film thereof |
| CN113276377A (en) * | 2021-05-26 | 2021-08-20 | 广东工业大学 | Preparation method of high-strength high-toughness polystyrene film |
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| CN116985444B (en) * | 2023-07-05 | 2024-04-02 | 广东汇发塑业科技有限公司 | Traction method for improving transmittance in degradation process of biodegradable film |
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