阅读说明：本技术 一种聚乳酸接枝改性天然纤维和pla复合材料及其制备方法 (Polylactic acid graft modified natural fiber and PLA composite material and preparation method thereof ) 是由 董奎勇 马博谋 何勇 王学利 俞建勇 于 2020-06-23 设计创作，主要内容包括：本发明涉及一种聚乳酸接枝改性天然纤维和PLA复合材料及其制备方法。该方法包括：将功能性天然纤维、功能性聚乳酸与溶剂混合,加入引发剂,点击化学反应。该方法能够有效改善两相界面,而且简单易行、适用于工业化生产；制备的天然纤维/聚乳酸复合材料、复合纤维具有更加优异的断裂强度、冲击强度和耐热性能。(The invention relates to a polylactic acid graft modified natural fiber and PLA composite material and a preparation method thereof. The method comprises the following steps: mixing the functional natural fiber, the functional polylactic acid and the solvent, adding an initiator, and carrying out click chemical reaction. The method can effectively improve the two-phase interface, is simple and feasible, and is suitable for industrial production; the prepared natural fiber/polylactic acid composite material and composite fiber have more excellent breaking strength, impact strength and heat resistance.)

1. A polylactic acid graft modification natural fiber is obtained by click chemical reaction of functional polylactic acid and functional natural fiber; the functional polylactic acid comprises linear polylactic acid or branched polylactic acid with double bonds or triple bonds at the tail end, and the functional natural fiber comprises natural fiber modified by azide or sulfydryl.

2. A preparation method of polylactic acid graft modified natural fiber comprises the following steps:

mixing functional natural fibers, functional polylactic acid and a solvent, adding an initiator, and carrying out click chemical reaction to obtain polylactic acid graft modified natural fibers, wherein the functional polylactic acid comprises linear polylactic acid or branched polylactic acid with terminal double bonds or triple bonds, the functional natural fibers comprise azide modified or sulfydryl modified natural fibers, and the mass ratio of the functional natural fibers to the functional polylactic acid is 1: 1-10.

3. The method of claim 2, wherein the natural fiber comprises bamboo fiber, hemp fiber, microcrystalline cellulose, cellulose nanocrystals, cellulose nanofibers, or wool; the weight average molecular weight of the functional polylactic acid is 1 × 10³-2×10⁴g/mol。

4. The method of claim 2, wherein the solvent comprises DMSO, DMAc, or toluene; the initiator is a photoinitiator or a thermal initiator.

5. The method of claim 2, wherein the click chemistry reaction is an azide-alkyne click chemistry reaction or a mercapto-alkene click chemistry reaction; the reaction temperature of the click chemistry is 0-200 ℃, and the reaction time of the click chemistry is 0.5-20 h.

6. A PLA composite material obtained by compounding the polylactic acid graft modified natural fiber according to claim 1 and a general PLA resin.

7. A PLA composite material is obtained by carrying out click chemical reaction on functional natural fibers, functional polylactic acid and common PLA resin; the functional polylactic acid comprises linear polylactic acid or branched polylactic acid with double bonds or triple bonds at the tail end, and the functional natural fiber comprises natural fiber modified by azide or sulfydryl.

8. A method of making the PLA composite of claim 6, comprising:

the PLA composite material is obtained by blending, injecting or spinning polylactic acid graft modified natural fibers and common PLA resin through a screw, wherein the mass percent of the natural fibers in the PLA composite material is 0.5-20%.

9. A method of making a PLA composite, comprising:

blending functional natural fibers, functional polylactic acid, common PLA resin and an initiator, and carrying out click chemical reaction to obtain a PLA composite material; wherein the functional polylactic acid comprises linear polylactic acid or branched polylactic acid with double bonds or triple bonds at the tail end, the functional natural fiber comprises natural fiber modified by azide or sulfydryl, and the mass percentage of the natural fiber in the PLA composite material is 0.5-20%.

10. Use of a PLA composite as claimed in claim 6 or 7.

Technical Field

The invention belongs to the field of polylactic acid materials and preparation thereof, and particularly relates to a polylactic acid graft modified natural fiber and PLA composite material and a preparation method thereof.

Background

Petroleum-based plastic products seriously threaten the living environment of human beings due to long degradation period, and the development of degradable plastics has great significance. Polylactic acid is the most actively studied environment-friendly material in recent years, has the outstanding advantages of good biocompatibility, degradability and the like, and is widely applied to the fields of packaging, spinning, agriculture, biomedicine and the like. However, the inherent defects of high brittleness, poor impact strength and the like become the bottleneck of further development of the polylactic acid material. The natural fiber is original in nature or directly obtained from artificially cultured plants and artificially bred animals, and has the advantages of easily available raw materials and excellent mechanical properties. In recent years, the development of natural fiber reinforced degradable polylactic acid composite materials is receiving wide attention, and related documents and patents are frequently reported. Chinese patent CN102167895A discloses a preparation method of a waste wool/polylactic acid ecological composite material, and specifically, the waste wool and polylactic acid are layered and mixed in a sandwich structure, and the composite material is prepared by a hot-press molding mode. Chinese patent CN206983409U discloses a preparation method of a bamboo fiber reinforced polylactic acid composite material, and specifically, the purpose of improving the mechanical property and the dimensional stability of bamboo fiber and polylactic acid in the compounding process is achieved through structural design. However, the natural fiber is heterogeneous with the polylactic acid matrix, and the interface adhesion is poor, which often results in poor reinforcing effect. When preparing natural fiber reinforced polylactic acid composite material, coordinating the interface combination between natural fiber and polylactic acid matrix is the key to solve the problem.

In recent years, research groups have used hydroxyl groups on cellulose to initiate lactide polymerization in situ to obtain CNC-g-PLLA, and prepared CNC-g-PLLA/PLA composite materials with excellent mechanical properties (polylactic/cellulose nanocrystals: the in situ polymerized polymers-hydrolysis advanced to advanced nanocomposites, European Polymer journal,2017,94: 173-). Also, in chinese patent CN107245231A, hemp fiber, cotton fiber, and bamboo fiber treated with sodium hydroxide are directly mixed with lactide for modification, and used for preparing polylactic acid composite material. However, the grafting method of "grafting from" generally has the disadvantages of low grafting efficiency and short grafted polylactic acid chain, and it is difficult to exert the reinforcing effect of the reinforcing material on the polylactic acid bulk.

Disclosure of Invention

The invention aims to solve the technical problem of providing a polylactic acid graft modified natural fiber and PLA composite material and a preparation method thereof, so as to overcome the defects of poor interface compatibility and poor reinforcing effect when natural fibers reinforce polylactic acid in the prior art. The invention solves the problem of interfacial compatibility between natural fibers and PLA resin through the modification of long-chain branched polylactic acid.

The invention provides a polylactic acid graft modified natural fiber, which is obtained by carrying out click chemical reaction on functional polylactic acid and functional natural fiber; the functional polylactic acid comprises linear polylactic acid or branched polylactic acid with double bonds or triple bonds at the tail end, and the functional natural fiber comprises natural fiber modified by azide or sulfydryl.

The invention also provides a preparation method of the polylactic acid graft modification natural fiber, which comprises the following steps:

mixing functional natural fibers, functional polylactic acid and a solvent, adding an initiator, and carrying out click chemical reaction to obtain polylactic acid graft modified natural fibers, wherein the functional polylactic acid comprises linear polylactic acid or branched polylactic acid with terminal double bonds or triple bonds, the functional natural fibers comprise azide modified or sulfydryl modified natural fibers, and the mass ratio of the functional natural fibers to the functional polylactic acid is 1: 1-10.

The natural fiber is plant fiber rich in cellulose component or protein fiber derived from animal.

The natural fiber comprises bamboo fiber, hemp fiber, microcrystalline cellulose, cellulose nanocrystal, cellulose nanofiber or wool.

The weight average molecular weight of the functional polylactic acid is 1 x 10³-2×10⁴g/mol。

The solvent includes DMSO, DMAc, or toluene.

The initiator is a photoinitiator or a thermal initiator.

The photoinitiator is benzoin dimethyl ether; the thermal initiator is azobisisobutyronitrile.

The click chemistry reaction is an azide-alkyne click chemistry reaction or a mercapto-alkene click chemistry reaction.

The click chemistry reaction temperature is 0-200 ℃, and the click chemistry reaction time is 0.5-20 h.

The invention also provides a PLA composite material which is obtained by compounding the polylactic acid graft modified natural fiber and common PLA resin.

The invention also provides a PLA composite material, which is obtained by carrying out click chemical reaction on functional natural fibers, functional polylactic acid and common PLA resin; the functional polylactic acid comprises linear polylactic acid or branched polylactic acid with double bonds or triple bonds at the tail end, and the functional natural fiber comprises natural fiber modified by azide or sulfydryl.

The invention also provides a preparation method of the PLA composite material, which comprises the following steps:

the PLA composite material is obtained by blending, injecting or spinning polylactic acid graft modified natural fibers and common PLA resin through a screw, wherein the mass percent of the natural fibers in the PLA composite material is 0.5-20%.

The screw temperature during blending is 160-230 ℃, and the blending time is 5-20 min.

The invention also provides a preparation method of the PLA composite material, which comprises the following steps:

blending functional natural fibers, functional polylactic acid, common PLA resin and an initiator, and carrying out click chemical reaction to obtain a PLA composite material; wherein the functional polylactic acid comprises linear polylactic acid or branched polylactic acid with double bonds or triple bonds at the tail end, the functional natural fiber comprises natural fiber modified by azide or sulfydryl, and the mass percentage of the natural fiber in the PLA composite material is 0.5-20%.

The screw temperature during blending is 160-230 ℃, and the blending time is 5-20 min.

The invention also provides an application of the PLA composite material.

According to the invention, end group functionalized polylactic acid is synthesized firstly, and then the polylactic acid is grafted on the surface of natural fiber under the action of light or heat in a 'grafting to' mode to prepare polylactic acid modified natural fiber, so that the controllable regulation of the length of the polylactic acid chain on the surface of the natural fiber is realized, the interface adhesion between the natural fiber and a polylactic acid matrix is enhanced, the homogenously modified natural fiber can effectively improve the interface compatibility with PLA, and then the homogenously modified natural fiber and PLA resin are used for preparing a composite material or fiber with excellent performance.

Drawings

FIG. 1 is a schematic representation of modified natural fibers made by click chemistry of the present invention.

FIG. 2 is a schematic diagram of the process for preparing the natural fiber polylactic acid composite material according to the present invention.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

The main reagent sources are as follows:

dimethyl sulfoxide (DMSO): the purity is more than or equal to 99.0 percent, and the product is purchased from chemical reagents of national drug group, Inc.;

dimethylacetamide (DMAc): the purity is more than or equal to 99.0 percent, and the product is purchased from chemical reagents of national drug group, Inc.;

toluene: the purity is more than or equal to 99.5 percent, and the product is purchased from chemical reagents of national drug group, Inc.;

l-lactide: the purity is more than or equal to 98 percent and is purchased from Shanghai Limited company of Aladdin reagent;

polylactic acid resin: designations 6201D, 4032D are both available from naturallworks, inc.

Good interfacial compatibility is demonstrated by the final composite properties, which are superior to those of comparative examples 1 and 2 under equivalent conditions as example 1.