CN102120817A - Crosslinking polylactic acid and preparation method thereof - Google Patents

Abstract

The invention relates to a cross-linked polylactic acid and a preparation method thereof: firstly, star-shaped polylactic acid is synthesized by ring-opening polymerization of lactide in the presence of a co-initiator, and then the end group is modified with an unsaturated acid anhydride. The product is obtained by initiating C=C double bond free radical polymerization by appropriate means to cross-link and solidify. The invention has the following advantages: under the same molecular weight, star-shaped polylactic acid has a lower melt viscosity than linear molecules, and is easy to process composite materials; adjusting the number and length of arms of star-shaped polylactic acid can change the cured product Cross-linking density; a variety of triggering methods are available to meet the different requirements of polylactic acid body and its composite materials.

Description

A kind of cross-linked polylactic acid and preparation method thereof

technical field

The invention relates to a cross-linked polylactic acid and a preparation method thereof.

Background technique

The growing awareness of environmental protection and energy shortage have aroused people's attention to the research, development and application of biodegradable materials. Among the many biodegradable polymer materials that have been developed, the research on the synthesis, preparation, processing and application of polylactic acid is the most active. Polylactic acid (PLA) is derived from renewable non-food crops (such as cassava, sugarcane, sweet sorghum, etc.), and its most prominent advantage is biodegradability. Pollution of the environment is very beneficial to the protection of the environment. So far, polylactic acid has been able to perform various molding processes like ordinary polymers. After secondary processing such as thermoforming and spinning, various films, sheets, and fibers prepared by it can be used in textiles, packaging, agriculture, medical care, and daily life. Daily necessities and other fields have obtained increasingly extensive application. However, PLA is a semi-crystalline polymer, and its glass transition temperature (T _g ) is only about 60°C. When the molded product exceeds this temperature during storage, transportation or use, it will deform. Poor heat resistance not only makes PLA unsuitable for heat-resistant containers such as lunch boxes, soup bowls, cups and other daily necessities, but also limits its application as engineering plastics in the fields of home appliances, electronic appliances, auto parts and aerospace.

Traditional methods to improve the heat resistance of PLA include increasing the crystallinity of PLA, blending with high T _g polymers, fiber reinforcement, and nanocomposites. Improving the crystallinity of PLA can be achieved by adding nucleating agents or changing the heat treatment process, but the maximum crystallinity that PLA can achieve is only 40% (Polymer, 2007, 48:6855~6866); PLA is a heat-resistant biodegradable resin. Therefore, improving the heat resistance of PLA by blending can only be achieved by introducing non-biodegradable resins, and the problems of large addition and poor compatibility are difficult to solve; the fiber reinforcement effect is also limited by compatibility, due to PLA The interface bonding between matrix and fiber is poor, so the heat resistance of PLA cannot be improved by pure fiber composite method (Composites Science and Technology, 2006, 66:1813~1824); nanocomposite is considered to improve the mechanical properties of PLA. An effective method for performance and heat resistance, and the required addition amount is low (2~8% by mass), but the performance of the composite material is strongly dependent on the degree of dispersion of the nanoparticles, although extending the melt blending time can achieve better However, it can also lead to significant degradation of PLA (Progress in Polymer Science, 2008, 33:820~852).

Cross-linking is a new method to improve the heat resistance and mechanical properties of PLA, but there are not many research reports at home and abroad. Chinese invention patents CN 101020781 and CN 101284934 respectively provide a preparation method of a heat-resistant polylactic acid-based composite material and a heat-resistant polylactic acid matrix resin. However, because these two methods directly use commercial linear polylactic acid and cross-linking agent to melt blend, not only the cross-linking density is low, but also the high melt viscosity is not convenient for the molding of composite materials.

In view of the above situation, the present invention provides a cross-linked polylactic acid and its preparation method, by synthesizing multi-armed star-shaped polylactic acid and modifying it, and then triggering the cross-linking of the modified star-shaped polylactic acid by appropriate means Reaction and solidification to improve the disadvantage of poor heat resistance of polylactic acid. The preparation process of the invention is simple, the preparation process is safe and environment-friendly, can significantly improve the heat resistance of polylactic acid, and has important practical application value.

Contents of the invention

The object of the present invention is to provide a kind of cross-linked polylactic acid and its preparation method.

The cross-linked polylactic acid proposed by the present invention first synthesizes star-shaped polylactic acid by ring-opening polymerization of lactide in the presence of a co-initiator, then uses unsaturated acid anhydride to modify its end group, and initiates it by appropriate means. The product is obtained by free radical polymerization and cross-linked curing. The molar ratio of each component in the star-shaped polylactic acid resin modified by the end group is as follows:

Component Molar ratio

Coinitiator 1

Lactide 7.5~60

Catalyst 0.0003~0.0048

Hydroquinone 0.01~0.08

Unsaturated acid anhydride 3.6~7.2.

In the present invention, the co-initiator is any one of glycerol, pentaerythritol or dipentaerythritol.

In the present invention, the lactide is any one of D-lactide, L-lactide or D, L-lactide and the like.

In the present invention, the catalyst is any one of Sn(Oct) ₂ , SnCl ₂ , Sn(OBu) ₂ , AlCl ₃ , Al(OPr) ₃ , FeCl ₃ , Fe(OEt) ₃ , ZnCl ₂ , HCl or HBr, etc. One, preferably Sn(Oct) ₂ .

In the present invention, the unsaturated acid anhydride is any one of methacrylic anhydride, maleic anhydride, allyl succinic anhydride, nonenyl succinic anhydride, dodecenyl succinic anhydride or dodecenyl succinic anhydride, etc. One, preferably methacrylic anhydride.

In the present invention, the means for initiating free radical polymerization includes any one of radiation initiation or free radical initiator thermal initiation, etc., and the thermal initiator is tert-butyl peroxybenzoate, cumene hydroperoxide , tert-butyl hydroperoxide, dicumyl peroxide or di-tert-butyl peroxide, etc.

The preparation method of the cross-linked polylactic acid that the present invention proposes, concrete steps are as follows:

(1) Dry the lactide under vacuum at 40°C for 24 hours;

(2) Add co-initiator and dry lactide in a molar ratio of 1:7.5~60 in a reaction vessel with inert gas, then add 0.004~0.008% lactide molar catalyst, stir and heat to 120~170℃, react for 2~5 hours, and the star-shaped polylactic acid can be obtained;

(3) Add 1-8% co-initiator molar hydroquinone to the product obtained in step (2), then add unsaturated acid anhydride at a ratio of 3.6-7.2 times the co-initiator molar mass, stir and heat to 110 At ~140°C, react in an inert gas environment for 2-5 hours to obtain end-modified star-shaped polylactic acid;

(4) After the functional modification of the terminal group in step (3), the terminal hydroxyl group of the star-shaped polylactic acid is replaced by an unsaturated group due to the esterification reaction, and the free radical of the C=C double bond can be induced by the following method Polymerization and cross-linking curing:

① Thermal initiation: At 100-130°C, add a free radical thermal initiator with a mass fraction of 0.5-2.0% to the modified product melt obtained in step (3), keep warm and stir for 5-10 minutes. Subsequently, the resin is poured into the mold and kept at 130-170°C for 1-3 hours, and finally post-cured at 180-200°C for 1-2 hours.

② Irradiation initiation: pour the modified product melt obtained in step (3) into a mold, and irradiate with a cobalt source at a dose of 50-100 kGy.

The beneficial effects of the present invention are: the synthesis process is simple, and the synthesis process is safe and environmentally friendly; under the same molecular weight, star polylactic acid has a lower melt viscosity than linear molecules, and is easy to process composite materials; the adjustment of star polylactic acid The number and length of the arms can change the crosslinking density of the cured product; a variety of triggering methods are available to meet the different requirements of the polylactic acid body and its composite materials during molding.

Detailed ways

The present invention is further illustrated below by way of examples.

Example 1:

(1) Add 0.92g of glycerol, 10.8g of dry L-lactide and 0.0012g of stannous octoate into a reaction vessel with an inert gas, stir and heat to 120°C, and react for 5 hours to obtain star shaped polylactic acid.

(2) Add 0.055 g of hydroquinone to the product obtained in step (1), then add 0.036 mol of methacrylic anhydride, stir and heat to 110°C, and react for 5 hours under an inert gas environment to obtain the terminal group modified Sexual star polylactic acid.

(3) Add 0.14 g of cumene hydroperoxide to the modified product melt obtained in step (2) at 100° C., keep warm and stir for 5 minutes. Subsequently, the resin is poured into the mold and kept at 160°C for 2 hours, and finally post-cured at 200°C for 1 hour.

The T _g of the cured product is 69°C, the sample can keep its original shape without deformation at 200°C, the temperature at which it loses 5% of its weight is 248°C, and the temperature at which it loses the most weight is 318°C.

Example 2:

(1) Add 1.36g of pentaerythritol, 14.4g of dry D,L-lactide and 0.0027g of stannous octoate into a reaction vessel with an inert gas, stir and heat to 130°C, and react for 4 hours to obtain star shaped polylactic acid.

(2) Add 0.080 g of hydroquinone to the product obtained in step (1), then add 0.050 mole of methacrylic anhydride, stir and heat to 120°C, and react for 4 hours under an inert gas environment to obtain the terminal group modified Sexualized star polylactic acid.

(3) Add 0.20 g of tert-butyl peroxybenzoate to the melt of the modified product obtained in step (2) at 110° C., keep warm and stir for 7 minutes. Subsequently, the resin is poured into the mold and kept at 130°C for 1 hour, and finally post-cured at 180°C for 1 hour.

The T _g of the cured product is 78°C, the sample can keep its original shape without deformation at 200°C, the temperature for 5% weight loss is 263°C, and the maximum weight loss rate temperature is 325°C.

Example 3:

(1) Add 2.54 grams of dipentaerythritol, 43.2 grams of dry L-lactide and 0.0071 grams of stannous octoate into a reaction vessel with an inert gas, stir and heat to 160 ° C, and react for 2 hours to obtain a star polylactic acid.

(2) Add 0.088 g of hydroquinone to the product obtained in step (1), then add 0.072 moles of methacrylic anhydride, stir and heat to 130°C, and react for 3 hours under an inert gas environment to obtain the terminal group modified Sexual star polylactic acid.

(3) At 120°C, add 0.85 g of tert-butyl hydroperoxide to the melt of the modified product obtained in step (2), keep warm and stir for 10 minutes. Subsequently, the resin is poured into the mold and kept at 170°C for 2 hours, and finally post-cured at 200°C for 2 hours.

The T _g of the cured product is 71°C, the sample can keep its original shape without deformation at 200°C, the temperature at which it loses 5% of its weight is 253°C, and the temperature at which it loses the most weight is 332°C.

Example 4:

(1) Add 0.68g of pentaerythritol, 28.8g of dry D,L-lactide and 0.0062g of stannous octoate into a reaction vessel with an inert gas, stir and heat to 170°C, and react for 2 hours to obtain star shaped polylactic acid.

(2) Add 0.045 g of hydroquinone to the product obtained in step (1), then add 0.024 mole of methacrylic anhydride, stir and heat to 140°C, and react for 2 hours under an inert gas environment to obtain the terminal group modified Sexual star polylactic acid.

(3) Pour the modified product melt obtained in step (2) into a mold, and irradiate with a cobalt source at a dose of 100 kGy.

The T _g of the cured product is 64°C, the sample can keep its original shape without deformation at 200°C, the temperature at which it loses 5% of its weight is 258°C, and the temperature at which it loses the most weight is 302°C.

Example 5:

(1) Add 0.92g of glycerol, 32.4g of dry L-lactide and 0.0036g of stannous octoate into a reaction vessel with an inert gas, stir and heat to 160°C, and react for 3 hours to obtain star shaped polylactic acid.

(2) Add 0.020 g of hydroquinone to the product obtained in step (1), then add 0.048 moles of methacrylic anhydride, stir and heat to 130 ° C, and react for 4 hours under an inert gas environment to obtain the terminal group modified Sexualized star polylactic acid.

(3) Pour the modified product melt obtained in step (2) into a mold, and irradiate with a cobalt source at a dose of 70kGy.

The T _g of the cured product is 65°C, the sample can keep its original shape without deformation at 200°C, the temperature for 5% weight loss is 249°C, and the maximum weight loss rate temperature is 310°C.

Claims (7)

1. cross-linking type poly(lactic acid), it is characterized in that: under the condition that coinitiator exists, synthesize the star poly(lactic acid) earlier by the rac-Lactide ring-opening polymerization, with unsaturated acid anhydride it is carried out terminal groups modification again, and cause or radical initiator thermal-initiated polymerization reaction and crosslinking curing obtains product by irradiation; The each component mol ratio is as follows in the star polylactic resin behind terminal groups modification:

The component mol ratio

Coinitiator 1

Rac-Lactide 7.5-60

Catalyzer 0.0003-0.0048

Resorcinol 0.01-0.08

Unsaturated acid anhydride 3.6-7.2.

2. cross-linking type poly(lactic acid) according to claim 1, it is characterized in that described coinitiator be in glycerol, tetramethylolmethane or the dipentaerythritol any.

3. cross-linking type poly(lactic acid) according to claim 1 is characterized in that described rac-Lactide is D-rac-Lactide, L-rac-Lactide or D, in the L-rac-Lactide any.

4. cross-linking type poly(lactic acid) according to claim 1 is characterized in that described catalyzer is Sn (Oct) ₂, SnCl ₂, Sn (OBu) ₂, AlCl ₃, Al (OPr) ₃, FeCl ₃, Fe (OEt) ₃, ZnCl ₂, among HCl or the HBr any.

5. cross-linking type poly(lactic acid) according to claim 1, it is characterized in that described unsaturated acid anhydride be in methacrylic anhydride, maleic anhydride, allyl group Succinic anhydried, nonenyl succinic acid acid anhydride, dodecenylsuccinic acid acid anhydride or the dodecenylsuccinic anhydride any.

6. cross-linking type poly(lactic acid) according to claim 1, it is characterized in that in the described initiation Raolical polymerizable employed thermal initiator be in peroxidized t-butyl perbenzoate, isopropyl benzene hydroperoxide, tertbutyl peroxide, dicumyl peroxide or the di-t-butyl peroxide any.

7. the preparation method of a cross-linking type poly(lactic acid) as claimed in claim 1 is characterized in that concrete steps are as follows:

(1) with rac-Lactide 40 ℃ of following vacuum-dryings 24 hours;

(2) in being connected with the reaction vessel of rare gas element, add coinitiator and exsiccant rac-Lactide by mole proportioning 1:7.5-60, the catalyzer that adds 0.004-0.008% rac-Lactide molar weight subsequently, stirring also is heated to 120-170 ℃, reacts 2-5 hour, promptly makes the star poly(lactic acid);

(3) add the Resorcinol of 1-8% coinitiator molar weight in step (2) products therefrom, ratio in 3.6-7.2 times of coinitiator molar weight adds unsaturated acid anhydride subsequently, stirring also is heated to 110-140 ℃, reaction is 2-5 hour under inert gas environment, promptly makes the star poly(lactic acid) behind the terminal groups modification;

(4) through the end group functional modification of step (3), the terminal hydroxy group of star poly(lactic acid) is replaced by unsaturated group because of esterification takes place, and can cause the two key generation Raolical polymerizables of C=C and crosslinking curing by following manner:

1. thermal initiation: under 100-130 ℃, adding massfraction in step (3) the gained modified product melt is the free radical thermal initiator of 0.5-2.0%, and insulation was also stirred 5-10 minute; Subsequently, resin is poured in the mould and at 130-170 ℃ to descend to be incubated 1-3 hour, got final product at 180-200 ℃ of following after fixing 1-2 hour at last;

2. irradiation causes: step (3) gained modified product melt is poured in the mould, get final product with cobalt source radiation 50-100kGy dosage.