CN109575545B - Fiber/polyurethane/polylactic acid blend and preparation method thereof - Google Patents

Abstract

The invention discloses a fiber/polyurethane/polylactic acid blend and a preparation method thereof. The fiber/polyurethane/polylactic acid blend is composed of polyester type thermoplastic polyurethane, polylactic acid and fiber, and the using amount of the fiber is 10-30% of the sum of the mass of the polyester type thermoplastic polyurethane and the mass of the polylactic acid; wherein the mass ratio of the polyester type thermoplastic polyurethane is 5-20% and the balance is polylactic acid, wherein the sum of the mass of the polyester type thermoplastic polyurethane and the mass of the polylactic acid is 100%; wherein: the polyester type thermoplastic polyurethane is polyester type thermoplastic polyurethane with an amorphous structure, and the soft segment accounts for 75-90% of the mass of the polyester type thermoplastic polyurethane according to the mass percentage, and the balance is the hard segment. Compared with pure polylactic acid, the blend provided by the invention has the advantages that the elongation at break and the tensile strength are obviously improved, and the glass transition temperature is not obviously reduced.

Description

Fiber/polyurethane/polylactic acid blend and preparation method thereof

Technical Field

The invention relates to a polylactic acid modified material, in particular to a fiber/polyurethane/polylactic acid blend and a preparation method thereof.

Background

With the increasing problems of "white waste" and traditional plastics on shortage of petroleum resources and environmental pollution, the demand of biodegradable plastics is increasing. Polylactic acid (PLA) is considered as the most promising biodegradable plastic due to its outstanding characteristics of good processability, mechanical properties, transparency, sufficient renewable raw material sources, etc. However, the high brittleness exhibited by polylactic acid is the biggest obstacle limiting its wide application. In order to improve the brittleness and toughness of polylactic acid, many enterprises and scientific research institutes have conducted a great deal of modification research on polylactic acid.

At present, the brittle modification method of polylactic acid mainly comprises the steps of adding a small-molecule plasticizer, blending with a flexible material and the like, but many reported methods have the defects of toughening and modifying the polylactic acid and greatly reducing the tensile strength and the glass transition temperature of the material. As shown in the literature, "study on the performance of several plasticizers on polylactic acid", the polylactic acid is plasticized by using polyethylene glycol (PEG), dioctyl phthalate (DOP), tributyl citrate (TBC), triphenyl phosphite (TPPi), and dibutyl sebacate (DBS), and the experimental results show that the several plasticizers significantly improve the elongation at break of the polylactic acid and also significantly reduce the tensile strength and glass transition temperature of the polylactic acid (zhangongwei, etc., modern plastic processing application, vol.19, No. 6, 2007, p 38-40). On the other hand, the small molecule plasticizer also has the problems of migration and precipitation, and the precipitation of the small molecule plasticizer further causes the reduction of the mechanical property of the material. For example, in the literature, "research on the influence of plasticizer on mechanical properties of P (3HB-co-4 HB)", P (3HB-co-4HB) is plasticized by using small-molecule plasticizer such as epoxidized soybean oil, tributyl acetate and the like, and the tensile strength and the elongation at break of a sample are reduced after the sample is placed for one month (blue, small, equal, plastics industry, volume 38 of 2010, supplement S0, P124-127).

The use of the macromolecular plasticizer does not have the problem of precipitation of the micromolecular plasticizer, but most of the macromolecular plasticizers also have the problem of obviously reducing the properties such as the tensile strength of the material. For example, in the document "preparation of biaxially stretched polylactic acid film", polylactic acid is toughened and modified by polybutylene carbonate, and when the content of polybutylene carbonate is 20%, the tensile strength of polylactic acid is reduced by 43% (luochaxin, master academic thesis, guangzhou: university of south china, see in particular document p34, tables 4-6). For another example, in the document "mechanical behavior and morphology research of polylactic acid/polyurethane blend", a twin-screw extruder is used to prepare a series of polylactic acid (PLA)/Thermoplastic Polyurethane (TPU) blends, a universal tester, a cantilever beam impact tester and a dynamic mechanical analyzer are used to test the mechanical properties of the PLA/TPU blends, and the samples and impact sections under different tensile states are respectively observed by a scanning electron microscope. The result shows that the elongation at break and the impact strength of the PLA/TPU blend are obviously increased along with the increase of the TPU content, the storage modulus is reduced, the loss modulus is increased, and the tensile section of the blend shows the evolution of a liquid drop state, a coarse fiber state and a fine fiber state; when the TPU content reached 40% (mass fraction, the same applies below), the elongation at break and impact strength of the PLA/TPU blend increased 300% and 13.5 times, respectively, over pure PLA (jiashiquine et al, chinese plastics, 2017, stage 03). However, when the content of the polyurethane is 20%, the elongation at break of the polylactic acid is increased by only 3.3 times, and the tensile strength is reduced by 33% (see section 2.1 of the document), and the toughening result is obviously not satisfactory.

Therefore, it is necessary to provide a polylactic acid modified material which can significantly improve the elongation at break and the tensile strength without significantly lowering the glass transition temperature thereof.

Disclosure of Invention

The invention aims to provide a fiber/polyurethane/polylactic acid blend which can obviously improve the elongation at break and the tensile strength of the obtained material and does not obviously reduce the glass transition temperature of the material, and a preparation method thereof.

The fiber/polyurethane/polylactic acid blend is characterized in that: the blend consists of polyester type thermoplastic polyurethane, polylactic acid and fiber, wherein the using amount of the fiber is 10-30% of the sum of the mass of the polyester type thermoplastic polyurethane and the mass of the polylactic acid; wherein the mass ratio of the polyester type thermoplastic polyurethane is 5-20% and the balance is polylactic acid, wherein the sum of the mass of the polyester type thermoplastic polyurethane and the mass of the polylactic acid is 100%; wherein:

the polyester type thermoplastic polyurethane is polyester type thermoplastic polyurethane with an amorphous structure, the polyester type thermoplastic polyurethane consists of a soft segment and a hard segment, in the composition of the polyester type thermoplastic polyurethane, the soft segment accounts for 75-90% of the mass of the polyester type thermoplastic polyurethane according to the mass percentage, and the balance is the hard segment; wherein the soft segment is polyester polyol with the number average molecular weight of 1000-.

The performance of the fiber/polyurethane/polylactic acid blend simultaneously meets the following three conditions (a) to (c):

(a) the elongation at break is improved by more than 1.5 times compared with that of pure polylactic acid;

(b) the tensile strength of the polylactic acid is improved by more than or equal to 10 percent relative to the pure polylactic acid;

(c) the glass transition temperature of the polylactic acid is reduced by less than or equal to 6 percent relative to the pure polylactic acid.

In the above condition (a), the elongation at break of the fiber/polyurethane/polylactic acid blend is generally increased by 2 to 14 times as compared with that of the pure polylactic acid, and in the condition (b), the tensile strength of the fiber/polyurethane/polylactic acid blend is generally increased by 12 to 23% as compared with that of the pure polylactic acid.

The test result of the applicant shows that the iron polyester type thermoplastic polyurethane is synthesized by selecting raw materials with specific parameters to obtain a soft segment and a hard segment according to a special proportion, and the iron polyester type thermoplastic polyurethane and polylactic acid are mixed according to the proportion of 5-20%: the polyurethane/polylactic acid blend prepared by a proportioning mode of 80-95% and 100% of the total amount can obviously improve the elongation at break of the modified material and does not obviously reduce the glass transition temperature and the tensile strength of the modified material; the tensile strength of the blend can be further improved by adding a specific amount of fiber to the blend.

In the technical scheme of the invention, the melt index of the polyester type thermoplastic polyurethane under the test condition of 190 ℃/2.16kg is 4-25g/10 min. The polylactic acid is conventional polylactic acid in the prior art, and the specific parameters are as follows: the glass transition temperature is 58.9-63.1 ℃, and the melt index under the test condition of 190 ℃/2.16kg is 2-10g/10 min.

In the technical scheme of the invention, the fiber is any one or the combination of more than two of cotton fiber, hemp fiber, wood fiber and bamboo fiber. The fiber is treated by conventional alkali liquor treatment and silane coupling agent treatment, and the alkali liquor treatment and the silane coupling agent treatment can be preferably carried out according to the following methods:

soaking the fiber in 50-80 deg.C alkali solution for 2-4 hr, taking out, soaking in 50-80 deg.C silane coupling agent solution with pH of 3-5 for 0.5-3 hr, taking out, and drying. Wherein the alkali solution can be aqueous solution of conventional alkaline substances (such as NaOH, KOH, etc.) with concentration of 4-15 wt%; the silane coupling agent is selected as in the prior art, specifically, the silane coupling agent can be any one or a combination of more than two selected from KH550, KH560, KH570 and the like, and the solvent used for preparing the silane coupling agent solution is a mixture of water and absolute ethyl alcohol according to the ratio of 1: 9-4: 6, the concentration of the silane coupling agent in the silane coupling agent solution is usually 3-5 wt%; the pH of the silane coupling agent solution is usually adjusted with a conventional inorganic acid such as hydrochloric acid or acetic acid.

In the technical scheme of the invention, the length of the fiber is preferably 2-6mm, and more preferably 2-4 mm. In order to enable the resulting fiber/polyurethane/polylactic acid blend to be completely degraded when needed later, the preferred fiber is a hemp fiber or a cotton fiber, wherein the hemp fiber can be one or a combination of more than two selected from sisal fiber, jute fiber, flax fiber and ramie fiber.

In the technical scheme of the invention, the polyester polyol is preferably any one or a combination of more than two selected from polyethylene glycol adipate (PEGA), poly (1, 2-propylene glycol adipate) (PPA) and poly (1, 4-butylene glycol adipate) (PBA). The isocyanate is preferably any one or the combination of more than two of diphenylmethane-4, 4' -diisocyanate (MDI), 1, 6-Hexamethylene Diisocyanate (HDI) and isophorone diisocyanate (IPDI). The alcohol chain extender is preferably one or a combination of more than two of Ethylene Glycol (EG), 1, 6-Hexanediol (HD) and 1, 4-Butanediol (BD).

The invention also provides a preparation method of the fiber/polyurethane/polylactic acid blend, which comprises the following steps:

1) weighing the raw materials according to the formula to prepare polyester type thermoplastic polyurethane;

2) and uniformly mixing the dried polyester type thermoplastic polyurethane, polylactic acid and fiber according to a formula, and performing melt extrusion on the obtained mixture to obtain the fiber/polyurethane/polylactic acid blend.

In step 1) of the preparation method, the polyester type thermoplastic polyurethane is prepared according to the conventional method, and the preparation method specifically comprises the following steps:

under the protection of dry nitrogen, putting the raw materials which are used as soft segments and are dehydrated for 1-3h at the temperature of 100-120 ℃ under the vacuum dehydration (-0.01MPa to-0.1 MPa) and isocyanate into a reaction kettle, uniformly mixing, keeping the system at 80-90 ℃, and carrying out heat preservation reaction for 1-3 h; and then cooling the system to be less than or equal to 60 ℃, adding a dried and metered alcohol chain extender under the stirring condition, uniformly mixing, heating to 70-90 ℃, keeping the temperature, reacting for 3-6h, taking out the material obtained by the reaction, and curing for 4-6h at the temperature of 100-120 ℃ to obtain the polyester type thermoplastic polyurethane. Wherein, the total mole number of the polyester diol and the alcohol chain extender is equivalent to the mole number of the isocyanate, the adding amount of the raw material used as the soft segment is controlled to be 75-90% of the mass ratio of the raw material in the polyester type thermoplastic polyurethane, and the total using amount of the isocyanate and the alcohol chain extender is controlled to be 10-25% of the mass ratio of the hard segment generated by the reaction of the isocyanate and the alcohol chain extender in the obtained polyester type thermoplastic polyurethane.

In step 2) of the above preparation method, the obtained mixture is usually melt blended in a twin-screw extruder, and then granulation and tabletting are carried out as required, so as to obtain the polyurethane/polylactic acid blend in the form of granules or sheets. The temperature at the time of the melt blending operation is the same as in the prior art, typically 180-. When the sheet is obtained by extrusion, the extrusion temperature is preferably controlled to be 180-200 ℃, and the temperature for cooling the cast sheet is preferably controlled to be 35-50 ℃.

Compared with the prior art, the invention is characterized in that:

1. the invention synthesizes the soft segment and the hard segment which are synthesized by selecting the raw materials with specific parameters according to a special proportion to form the polyester type thermoplastic polyurethane, and the polyester type thermoplastic polyurethane and the polylactic acid are mixed according to the proportion of 5-20 percent: the polyurethane/polylactic acid blend prepared by a proportioning mode of 80-95% and 100% of the total amount can obviously improve the elongation at break of the modified material and does not obviously reduce the glass transition temperature and the tensile strength of the modified material; on the basis, a specific amount of fiber is added, so that the tensile strength of the obtained blend is further improved on the basis of ensuring the performances, and the defects that the tensile strength and the glass transition temperature of the material are obviously sacrificed when the high elongation at break of the modified polylactic acid in the prior art is effectively improved.

2. The invention adopts the macromolecular plasticizer, and the problem that the performance of the toughened material is reduced due to the migration and precipitation of the micromolecular plasticizer is solved.

3. The raw materials involved in the invention are easy to obtain, and the method is simple and easy to operate.

Detailed Description

The present invention will be better understood from the following detailed description of specific examples, which should not be construed as limiting the scope of the present invention.

The TPU, PLA, various isocyanates (MDI, HDI or IPDI) and various alcohol chain extenders (EG, BD or HD) referred to in the following examples were subjected to vacuum dehydration (-0.1MPa, dehydration at 120 ℃ for 1-3h) (the water content of the resulting material was less than 200ppm), and no further details were given in the examples.

Example 1

1) Putting 8kg of PEGA with the number average molecular weight of 1800 and 1.824kg of isocyanate (MDI) into a reaction kettle, uniformly mixing, keeping the system at 85 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.176kg of alcohol chain Extender (EG) under the stirring condition, uniformly mixing, heating to 70 ℃, keeping the temperature, reacting for 5 hours, taking out materials obtained by the reaction, and curing for 4 hours in a 120 ℃ oven to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 20%, the mass ratio of the soft segment in the TPU is 80%, and the melt index of the obtained TPU is 8g/10min (under the test condition of 190 ℃/2.16kg, the same applies below);

2) soaking ramie fiber with length of 2-4mm in 4 wt% NaOH aqueous solution at 60 deg.C for 3h, taking out, draining, and adding 3 wt% KH550 solution (pH 3, solvent is prepared from water and anhydrous ethanol according to a ratio of 1: 9 volume ratio) for 3 hours to obtain the treated ramie fibers;

3) 2.0kg of the TPU obtained in the step 1), 3kg of the fiber obtained in the step 2) and 8.0kg of PLA with the melt index of 2g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength was 51.7MPa, the elongation at break was 151.05%, and the glass transition temperature was 59.5 ℃.

Comparative example 1

PLA with the melt index of 2g/10min is placed in a double-screw extruder for melt blending, extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the polylactic acid sheet.

The tensile strength, elongation at break and glass transition temperature of the polylactic acid sheet obtained in the comparative example were measured, and the results were: the tensile strength is 47.0MPa, the elongation at break is 10.07 percent, and the glass transition temperature is 63.1 ℃.

Example 1 compared to comparative example 1, the sheet obtained in example 1 showed a 14-fold increase in elongation at break, a 10% increase in tensile strength, and a 5.71% decrease in glass transition temperature, relative to the sheet obtained in comparative example 1.

Example 2

1) Placing 9kg of PPA with the number average molecular weight of 2500 and 0.974kg of isocyanate (MDI) in a reaction kettle, uniformly mixing, keeping the system at 85 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.026kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 5 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU, wherein the mass ratio of a hard segment in the TPU is 10%, the mass ratio of a soft segment in the TPU is 90%, and the melt index of the obtained TPU is 11g/10 min;

2) soaking 2-4mm jute fiber in 15 wt% concentration NaOH water solution at 60 deg.C for 3 hr, draining, adding 5 wt% KH550 solution at 80 deg.C (pH 4, solvent is 2: mixed solvent composed of 8 volume ratio) for 0.5h to obtain the treated jute fiber;

3) 2.0kg of the TPU obtained in the step 1), 2.5kg of the fiber obtained in the step 2) and 8.0kg of PLA with the melt index of 6g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and is extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 50.71MPa, the elongation at break is 153.15 percent, and the glass transition temperature is 56.7 ℃.

Comparative example 2-1

PLA with the melt index of 6g/10min is placed in a double-screw extruder for melt blending, extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the polylactic acid sheet.

The tensile strength, elongation at break and glass transition temperature of the polylactic acid sheet obtained in the comparative example were measured, and the results were: the tensile strength is 46.1MPa, the elongation at break is 10.21 percent, and the glass transition temperature is 60.3 ℃.

Example 2 compared to comparative example 2-1, the sheet obtained in example 2 showed a 14-fold increase in elongation at break, a 10% increase in tensile strength, and a 5.97% decrease in glass transition temperature, relative to the sheet obtained in comparative example 2-1.

Comparative examples 2 to 2

2kg of triphenyl phosphite and 8kg of PLA with the melt index of 6g/10min are placed in a double-screw extruder for melt blending, extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the triphenyl phosphite/polylactic acid sheet.

The tensile strength, elongation at break and glass transition temperature of the triphenyl phosphite/polylactic acid sheet obtained in the comparative example were measured, and the results were: the tensile strength was 20.1MPa, the elongation at break was 573.4%, and the glass transition temperature was 33.4 ℃.

Comparative example 2-2 compared with comparative example 2-1, the elongation at break of the sheet obtained in comparative example 2-2 was increased 55.16 times, the tensile strength was decreased 56.40%, and the glass transition temperature was decreased 44.61% as compared with the sheet obtained in comparative example 2-1.

Comparative examples 2 to 3

2kg of polybutylene carbonate and 8kg of PLA with the melt index of 6g/10min are placed in a double-screw extruder for melt blending, extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the polybutylene carbonate/polylactic acid sheet.

The tensile strength, elongation at break and glass transition temperature of the polybutylene carbonate/polylactic acid sheet obtained in the comparative example were measured, and the results were as follows: the tensile strength is 23.1MPa, the elongation at break is 16.89%, and the glass transition temperature is 42.1 ℃.

Comparative examples 2-3 compared with comparative example 2-1, the sheet obtained in comparative examples 2-3 showed an increase in elongation at break of 0.65 times, a decrease in tensile strength of 49.89%, and a decrease in glass transition temperature of 30.18% as compared with the sheet obtained in comparative example 2-1.

Example 3

1) Putting 8.5kg of PEGA with the number average molecular weight of 2500 and 1.371kg of isocyanate (MDI) into a reaction kettle, uniformly mixing, keeping the system at 90 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.129kg of alcohol chain Extender (EG) under the stirring condition, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 4 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 15 percent, the mass ratio of the soft segment in the TPU is 85 percent, and the melt index of the obtained TPU is 18g/10 min;

2) placing sisal fiber with length of 2-4mm in KOH aqueous solution with temperature of 60 deg.C and concentration of 12 wt% for 3h, taking out, draining, placing in KH550 solution with temperature of 60 deg.C and concentration of 3 wt% (pH 4, solvent is 4: mixed solvent composed of 6 volume ratio) for 3 hours to obtain the treated sisal fibers;

3) 2.0kg of the TPU obtained in the step 1), 1.5kg of the fiber obtained in the step 2) and 8.0kg of PLA with the melt index of 10g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and is extruded (180 ℃) and cooled by a cooling roller at 35 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 53.21MPa, the elongation at break is 153.15%, and the glass transition temperature is 57.1 ℃.

Comparative example 3

PLA with the melt index of 10g/10min is placed in a double-screw extruder for melt blending, extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the polylactic acid sheet.

The tensile strength, elongation at break and glass transition temperature of the polylactic acid sheet obtained in the comparative example were measured, and the results were: the tensile strength is 45.7MPa, the elongation at break is 10.36 percent, and the glass transition temperature is 58.9 ℃.

Example 3 compared to comparative example 3, the sheet obtained in example 3 showed a 14-fold increase in elongation at break, a 10% increase in tensile strength, and a 3.05% decrease in glass transition temperature, relative to the sheet obtained in comparative example 3.

Example 4

1) Putting 8kg of PEGA with the number average molecular weight of 1000 and 1.824kg of isocyanate (HDI) into a reaction kettle, uniformly mixing, keeping the system at 90 ℃, and carrying out heat preservation reaction for 1 h; then cooling the system to 60 ℃, adding 0.176kg of alcohol chain Extender (EG) under the stirring condition, uniformly mixing, heating to 70 ℃, keeping the temperature, reacting for 4 hours, taking out materials obtained by the reaction, and curing for 4 hours in a 120 ℃ oven to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 20 percent, the mass ratio of the soft segment in the TPU is 80 percent, and the melt index of the obtained TPU is 6g/10 min;

2) soaking cotton fiber with length of 2-4mm in 10 wt% NaOH aqueous solution at 60 deg.C for 4h, taking out, draining, and adding 3 wt% KH570 solution (pH 5, solvent is 3: 7 volume ratio) for 3 hours to obtain the processed cotton fiber;

3) 2.0kg of the TPU obtained in the step 1), 1.5kg of the fiber obtained in the step 2) and 8.0kg of PLA with the melt index of 6g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and is extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 51.86MPa, the elongation at break is 152.49 percent, and the glass transition temperature is 57.6 ℃.

Example 5

1) Placing 7.5kg of PPA with the number average molecular weight of 1000 and 2.260kg of isocyanate (IPDI) in a reaction kettle, uniformly mixing, keeping the system at 90 ℃, and reacting for 1h under heat preservation; then cooling the system to 60 ℃, adding 0.240kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 6 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 25 percent, the mass ratio of the soft segment in the TPU is 75 percent, and the melt index of the obtained TPU is 4g/10 min;

2) soaking bamboo fiber with length of 2-6mm in 6 wt% KOH aqueous solution at 60 deg.C for 4h, taking out, draining, and placing in 3 wt% KH590 solution (pH 3, solvent is prepared from water and anhydrous ethanol by mixing at 2: mixed solvent composed of 8 volume ratios) for 3 hours to obtain the processed carbon fiber;

3) 1.5kg of the TPU obtained in the step 1), 2.5kg of the fiber obtained in the step 2) and 8.5kg of PLA with the melt index of 2g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and is extruded (210 ℃) and cooled by a cooling roller at 50 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 52.64MPa, the elongation at break is 140.98 percent, and the glass transition temperature is 62.1 ℃.

Example 6

1) Putting 8.5kg of PEGA with the number average molecular weight of 2500 and 1.242kg of isocyanate (IPDI) into a reaction kettle, uniformly mixing, keeping the system at 90 ℃, and carrying out heat preservation reaction for 1 h; then cooling the system to 60 ℃, adding 0.258kg of alcohol chain extender (HD) under the condition of stirring, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 3 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 15 percent, the mass ratio of the soft segment in the TPU is 85 percent, and the melt index of the obtained TPU is 25g/10 min;

2) wood fiber with the length of 2-4mm is taken and placed in KOH aqueous solution with the temperature of 70 ℃ and the concentration of 8 wt% for soaking for 3h, the wood fiber is taken out, drained and placed in KH570 solution with the temperature of 60 ℃ and the concentration of 3 wt% (pH is 3, and the solvent is prepared by mixing water and absolute ethyl alcohol according to the weight ratio of 1: 9 volume ratio) for 2 hours to obtain the processed nylon fiber;

3) 1.5kg of the TPU obtained in the step 1), 2kg of the fiber obtained in the step 2) and 8.5kg of PLA with the melt index of 10g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (180 ℃) and cooled by a cooling roller at 35 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 51.86MPa, the elongation at break is 144.36.1 percent, and the glass transition temperature is 55.4 ℃.

Example 7

1) 8kg of PBA with the number average molecular weight of 1500 and 1.703kg of isocyanate (HDI) are placed in a reaction kettle, and after uniform mixing, the system is kept at 80 ℃ for heat preservation reaction for 2 h; then cooling the system to 60 ℃, adding 0.297kg of alcohol chain Extender (EG) under the stirring condition, uniformly mixing, heating to 70 ℃, keeping the temperature, reacting for 6 hours, taking out materials obtained by the reaction, and curing for 4 hours in a 120 ℃ oven to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 20 percent, the mass ratio of the soft segment in the TPU is 80 percent, and the melt index of the obtained TPU is 15g/10 min;

2) soaking flax fiber with length of 2-6mm in 6 wt% KOH aqueous solution at 60 deg.C for 2h, taking out, draining, and adding 3 wt% KH550 solution at 70 deg.C (pH 3, solvent is 2: mixed solvent composed of 8 volume ratios) for 1.5h to obtain the treated polyester fiber;

3) 1.5kg of the TPU obtained in the step 1), 2.8kg of the fiber obtained in the step 2) and 8.5kg of PLA with the melt index of 6g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and is extruded (185 ℃) and cooled by a cooling roller at 42 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 52.57MPa, the elongation at break is 140.76%, and the glass transition temperature is 59.8 ℃.

Example 8

1) Putting 8.5kg of PEGA with the number average molecular weight of 2000 and 1.413kg of isocyanate (MDI) into a reaction kettle, uniformly mixing, keeping the system at 80 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.087kg of alcohol chain Extender (EG) under the stirring condition, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 6 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 15 percent, the mass ratio of the soft segment in the TPU is 85 percent, and the melt index of the obtained TPU is 2g/10 min;

2) soaking sisal fiber with length of 2-4mm in 10 wt% NaOH aqueous solution at 60 deg.C for 2h, taking out, draining, and placing in 3 wt% KH560 solution (pH 3, solvent is 3: 7 volume ratio) for 3 hours to obtain the treated sisal fibers;

3) 1.5kg of the TPU obtained in the step 1), 2kg of the fiber obtained in the step 2) and 8.5kg of PLA with the melt index of 2g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (185 ℃) and cooled by a cooling roller at the temperature of 45 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength was 53.73MPa, the elongation at break was 127.60%, and the glass transition temperature was 62.3 ℃.

Example 9

1) 8kg of PBA with the number average molecular weight of 2200 and 1.656kg of isocyanate (IPDI) are put into a reaction kettle and are uniformly mixed, and then the system is kept at 80 ℃ for heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.344kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 90 ℃, carrying out heat preservation reaction for 3 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 20 percent, the mass ratio of the soft segment in the TPU is 80 percent, and the melt index of the obtained TPU is 13g/10 min;

2) taking sisal fiber and cotton fiber with the length of 2-4mm (the weight ratio is 2: 1) soaking in 10 wt% NaOH aqueous solution at 60 deg.C for 2 hr, taking out, draining, and adding into 3 wt% KH570 solution (pH 3, solvent is prepared from water and anhydrous ethanol at a ratio of 1: 9 volume ratio) for 3 hours to obtain the treated sisal fibers;

3) 1.0kg of the TPU obtained in the step 1), 3kg of the fiber obtained in the step 2) and 9.0kg of PLA with the melt index of 6g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (185 ℃) and cooled by a cooling roller at 40 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 54.32MPa, the elongation at break is 63.12%, and the glass transition temperature is 58.1 ℃.

Example 10

1) Putting 7.5kg of PEGA with the number average molecular weight of 1000 and 2.335kg of isocyanate (MDI) into a reaction kettle, uniformly mixing, keeping the system at 80 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.165kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 6 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 25 percent, the mass ratio of the soft segment in the TPU is 75 percent, and the melt index of the obtained TPU is 17g/10 min;

2) selecting ramie fibers and flax fibers with the length of 2-4mm (the weight ratio is 1: 1) soaking in 6 wt% NaOH aqueous solution at 60 deg.C for 4 hr, taking out, draining, and adding into 3 wt% KH550 solution (pH 4, solvent is prepared from water and anhydrous ethanol at a ratio of 1: 9 volume ratio) for 2 hours to obtain the treated fiber;

3) 1.0kg of the TPU obtained in the step 1), 2.8kg of the fiber obtained in the step 2) and 9.0kg of PLA with the melt index of 2g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and is extruded (190 ℃) and cooled by a cooling roller at 45 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 52.56MPa, the elongation at break is 72.34 percent, and the glass transition temperature is 59.8 ℃.

Example 11

1) Putting 8kg of PPA with the number average molecular weight of 1300 and 1.818kg of isocyanate (IPDI) into a reaction kettle, uniformly mixing, keeping the system at 80 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.182kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 6 hours, taking out the materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 20 percent, the mass ratio of the soft segment in the TPU is 80 percent, and the melt index of the obtained TPU is 10g/10 min;

2) soaking sisal fiber with length of 2-4mm in 10 wt% NaOH aqueous solution at 60 deg.C for 4h, taking out, draining, and placing in 3 wt% KH550 solution (pH 4, solvent is 2: mixed solvent composed of 8 volume ratio) for 2.5h to obtain the treated sisal fibers;

3) 1.0kg of the TPU obtained in the step 1), 2kg of the fiber obtained in the step 2) and 9.0kg of PLA with the melt index of 10g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (190 ℃) and cooled by a cooling roller at the temperature of 45 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength was 53.12MPa, the elongation at break was 63.78%, and the glass transition temperature was 55.9 ℃.

Example 12

1) Putting 8kg of PEGA with the number average molecular weight of 1500 and 1.868kg of isocyanate (MDI) into a reaction kettle, uniformly mixing, keeping the system at 85 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.132kg of alcohol chain Extender (EG) under the stirring condition, uniformly mixing, heating to 70 ℃, keeping the temperature, reacting for 6 hours, taking out materials obtained by the reaction, and curing for 4 hours in a 120 ℃ oven to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 20 percent, the mass ratio of the soft segment in the TPU is 80 percent, and the melt index of the obtained TPU is 12g/10 min;

2) soaking ramie fibers with the length of 2-4mm in a 12 wt% NaOH aqueous solution at the temperature of 60 ℃ for 3h, taking out, draining, and placing in KH570 and KH550 (according to the weight ratio of 1: 1) solution (pH 3, solvent was prepared from water and absolute ethanol at a ratio of 4: mixed solvent composed of 6 volume ratio) for 1 hour to obtain the treated ramie fiber;

3) 1.0kg of the TPU obtained in the step 1), 1.5kg of the fiber obtained in the step 2) and 9.0kg of PLA with the melt index of 2g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and is extruded (200 ℃) and cooled by a cooling roller at 50 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 55.12MPa, the elongation at break is 76.45 percent, and the glass transition temperature is 59.7 ℃.

Example 13

1) 8.5kg of PBA with the number average molecular weight of 1500 and 1.309kg of isocyanate (HDI) are placed in a reaction kettle and are uniformly mixed, and then the system is kept at 90 ℃ for heat preservation reaction for 3 hours; then cooling the system to 55 ℃, adding 0.191kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 5 hours, taking out the glue solution, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 15 percent, the mass ratio of the soft segment in the TPU is 85 percent, and the melt index of the obtained TPU is 10g/10 min;

2) soaking 2-4mm jute fiber in 8 wt% concentration NaOH water solution at 60 deg.C for 2 hr, draining, adding 3 wt% KH550 solution at 70 deg.C (pH 3, solvent is prepared from water and anhydrous ethanol by mixing 1: 9 volume ratio) for 1.5h to obtain the treated jute fiber;

3) 0.5kg of the TPU obtained in the step 1), 2kg of the fiber obtained in the step 2) and 9.5kg of PLA with the melt index of 2g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (195 ℃) and cooled by a cooling roller at 40 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 57.81MPa, the elongation at break is 25.18%, and the glass transition temperature is 62.7 ℃.

Example 13 compared to comparative example 1, the sheet obtained in example 13 showed a 1.5-fold increase in elongation at break, a 23% increase in tensile strength, and a 0.63% decrease in glass transition temperature, relative to the sheet obtained in comparative example 1.

Example 14

1) Putting 8.5kg of PEGA with the number average molecular weight of 1800 and 1.370kg of isocyanate (IPDI) into a reaction kettle, uniformly mixing, keeping the system at 80 ℃, and carrying out heat preservation reaction for 3 hours; then cooling the system to 50 ℃, adding 0.130kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 80 ℃, carrying out heat preservation reaction for 4 hours, taking out the materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 15 percent, the mass ratio of the soft segment in the TPU is 85 percent, and the melt index of the obtained TPU is 12g/10 min;

2) placing sisal fiber with length of 2-4mm in KOH aqueous solution with temperature of 60 deg.C and concentration of 6 wt% for soaking for 2h, taking out, draining, placing in KH560 solution with temperature of 80 deg.C and concentration of 3 wt% (pH of 3, solvent is 3: 7 volume ratio) for 3 hours to obtain the treated sisal fibers;

3) 0.5kg of the TPU obtained in the step 1), 2kg of the fiber obtained in the step 2) and 9.5kg of PLA with the melt index of 6g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (185 ℃) and cooled by a cooling roller at the temperature of 45 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 56.71MPa, the elongation at break is 25.53 percent, and the glass transition temperature is 57.6 ℃.

Example 14 compared to comparative example 2-1, the sheet obtained in example 14 showed a 1.5-fold increase in elongation at break, a 23% increase in tensile strength, and a 4.48% decrease in glass transition temperature, relative to the sheet obtained in comparative example 2-1.

Example 15

1) Putting 8kg of PEGA with the number average molecular weight of 2100 and 1.723kg of isocyanate (MDI) in a reaction, uniformly mixing, keeping the system at 80 ℃, and reacting for 2 hours in a heat preservation way; then cooling the system to 60 ℃, adding 0.277kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 70 ℃, carrying out heat preservation reaction for 6 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 20 percent, the mass ratio of the soft segment in the TPU is 80 percent, and the melt index of the obtained TPU is 14g/10 min;

2) soaking ramie fiber with length of 2-4mm in 10 wt% KOH aqueous solution at 60 deg.C for 3h, taking out, draining, and adding 3 wt% KH570 solution (pH 3, solvent is prepared from water and anhydrous ethanol according to a ratio of 1: 9 volume ratio) for 3 hours to obtain the treated ramie fibers;

3) 0.5kg of the TPU obtained in the step 1), 1kg of the fiber obtained in the step 2) and 9.5kg of PLA with the melt index of 10g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (200 ℃) and cooled by a cooling roller at 40 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 56.22MPa, the elongation at break is 25.91 percent, and the glass transition temperature is 58.3 ℃.

Example 15 compared to comparative example 3, the sheet obtained in example 15 showed a 1.5-fold increase in elongation at break, a 23% increase in tensile strength, and a 1.02% decrease in glass transition temperature, relative to the sheet obtained in comparative example 3.

Example 16

1) Putting 7.5kg of PEGA with the number average molecular weight of 1800 and 1.628kg of isocyanate (HDI) into a reaction kettle, uniformly mixing, keeping the system at 80 ℃, and carrying out heat preservation reaction for 2 h; then cooling the system to 60 ℃, adding 0.497kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 90 ℃, keeping the temperature, reacting for 3 hours, taking out materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 25 percent, the mass ratio of the soft segment in the TPU is 75 percent, and the melt index of the obtained TPU is 14g/10 min;

2) soaking 2-4mm long Boehmeria Boehmerina fiber in 12 wt% NaOH aqueous solution at 60 deg.C for 2 hr, taking out, draining, and placing in 3 wt% KH550 solution (pH 3, solvent is 2: 8 volume ratio) for 2 hours to obtain the treated ramie fibers;

3) 0.5kg of the TPU obtained in the step 1), 1kg of the fiber obtained in the step 2) and 9.5kg of PLA with the melt index of 6g/10min are uniformly mixed, the obtained mixture is placed in a double-screw extruder for melt blending, and the mixture is extruded (190 ℃) and cooled by a cooling roller at the temperature of 45 ℃ to obtain the fiber/polyurethane/polylactic acid sheet.

The sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 55.82MPa, the elongation at break is 28.79 percent, and the glass transition temperature is 60.1 ℃.

Example 17

Example 16 was repeated, except that:

the step 1) is carried out according to the following operations:

putting 7.5kg of PEGA with the number average molecular weight of 1800, 0.830kg of isocyanate (HDI) and 1.236kg of isocyanate (MDI) into a reaction kettle, uniformly mixing, keeping the system at 80 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.035kg of alcohol chain extender (BD) and 0.024kg of chain Extender (EG) under the condition of stirring, uniformly mixing, heating to 90 ℃, keeping the temperature and reacting for 3 hours, taking out materials obtained by the reaction, and curing for 4 hours in a 120 ℃ oven to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 25 percent, the mass ratio of the soft segment in the TPU is 75 percent, and the melt index of the obtained TPU is 15g/10 min;

the sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 53.21MPa, the elongation at break is 27.56 percent, and the glass transition temperature is 60.2 ℃.

Example 18

Example 16 was repeated, except that:

the step 1) is carried out according to the following operations:

putting 7.5kg of PEGA with the number average molecular weight of 1800, 0.312kg of isocyanate (HDI), 0.696kg of isocyanate (MDI) and 1.031kg of isocyanate (IPDI) into a reaction kettle, uniformly mixing, keeping the system at 80 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.460kg of alcohol chain extender (BD) under the stirring condition, uniformly mixing, heating to 90 ℃, carrying out heat preservation reaction for 3 hours, taking out the materials obtained by the reaction, and curing in a 120 ℃ oven for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 25 percent, the mass ratio of the soft segment in the TPU is 75 percent, and the melt index of the obtained TPU is 16g/10 min;

the sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 55.46MPa, the elongation at break is 28.69 percent, and the glass transition temperature is 60.0 ℃.

Example 19

Example 8 was repeated except that:

the step 1) is carried out according to the following operations:

putting 1.141kg of PEGA with the number average molecular weight of 1000, 3.081kg of PBA with the number average molecular weight of 1800, 4.279kg of PPA with the number average molecular weight of 1500 and 1.480kg of isocyanate (MDI) into a reaction kettle, uniformly mixing, keeping the system at 80 ℃, and carrying out heat preservation reaction for 2 hours; then cooling the system to 60 ℃, adding 0.003kg of alcohol chain Extender (EG), 0.006kg of alcohol chain extender (BD) and 0.012kg of alcohol chain extender (HD) under the condition of stirring, uniformly mixing, heating to 90 ℃, carrying out heat preservation reaction for 3 hours, taking out the materials obtained by the reaction, and curing in an oven at 120 ℃ for 4 hours to obtain the TPU; the mass ratio of the hard segment in the obtained TPU to the TPU is 25 percent, the mass ratio of the soft segment in the TPU is 75 percent, and the melt index of the obtained TPU is 17g/10 min;

the sheet obtained in this example was tested for tensile strength, elongation at break and glass transition temperature and found to be: the tensile strength is 54.55MPa, the elongation at break is 129.36%, and the glass transition temperature is 62.4 ℃.

Claims (9)

1. A fiber/polyurethane/polylactic acid blend characterized by: the blend consists of polyester type thermoplastic polyurethane, polylactic acid and fiber, wherein the using amount of the fiber is 10-30% of the sum of the mass of the polyester type thermoplastic polyurethane and the mass of the polylactic acid; wherein the mass ratio of the polyester type thermoplastic polyurethane is 5-20% and the balance is polylactic acid, wherein the sum of the mass of the polyester type thermoplastic polyurethane and the mass of the polylactic acid is 100%; wherein:

the polyester type thermoplastic polyurethane is polyester type thermoplastic polyurethane with an amorphous structure, the polyester type thermoplastic polyurethane consists of a soft segment and a hard segment, in the composition of the polyester type thermoplastic polyurethane, the soft segment accounts for 75-90% of the mass of the polyester type thermoplastic polyurethane according to the mass percentage, and the balance is the hard segment; wherein the soft segment is polyester polyol with the number average molecular weight of 1000-;

the performance of the blend simultaneously satisfies the following three conditions (a) to (c):

(a) the elongation at break is improved by more than 1.5 times compared with that of pure polylactic acid;

(b) the tensile strength of the polylactic acid is improved by more than or equal to 10 percent relative to the pure polylactic acid;

(c) the glass transition temperature of the polylactic acid is reduced by less than or equal to 6 percent relative to the pure polylactic acid.

2. The fiber/polyurethane/polylactic acid blend according to claim 1, wherein: in condition (a), the elongation at break of the blend is increased by a factor of 2 to 14 relative to the pure polylactic acid; in the condition (b), the tensile strength of the blend is increased by 12 to 23% relative to the pure polylactic acid.

3. The fiber/polyurethane/polylactic acid blend according to claim 1 or 2, characterized in that: the melt index of the polyester type thermoplastic polyurethane under the test condition of 190 ℃/2.16kg is 4-25g/10 min.

4. The fiber/polyurethane/polylactic acid blend according to claim 1 or 2, characterized in that: the fiber is one or the combination of more than two of cotton fiber, hemp fiber, carbon fiber, wood fiber and bamboo fiber.

5. The fiber/polyurethane/polylactic acid blend according to claim 1 or 2, characterized in that: the length of the fiber is 2-6 mm.

6. The fiber/polyurethane/polylactic acid blend according to claim 1 or 2, characterized in that: the polyester polyol is one or the combination of more than two of polyethylene glycol adipate, polypropylene glycol adipate and polybutylene glycol adipate.

7. The fiber/polyurethane/polylactic acid blend according to claim 1 or 2, characterized in that: the isocyanate is one or the combination of more than two of diphenylmethane-4, 4' -diisocyanate, 1, 6-hexamethylene diisocyanate and isophorone diisocyanate.

8. The fiber/polyurethane/polylactic acid blend according to claim 1 or 2, characterized in that: the alcohol chain extender is any one or the combination of more than two of ethylene glycol, 1, 6-hexanediol and 1, 4-butanediol.

9. A method of preparing the fiber/polyurethane/polylactic acid blend of claim 1, comprising the steps of:

1) weighing the raw materials according to the formula to prepare polyester type thermoplastic polyurethane;

2) and uniformly mixing the dried polyester type thermoplastic polyurethane, polylactic acid and fiber according to a formula, and performing melt extrusion on the obtained mixture to obtain the fiber/polyurethane/polylactic acid blend.