CN102604293A - Thermoplastically processable polyvinyl alcohol composite and preparation method thereof - Google Patents

Abstract

The invention relates to a thermoplastically processable polyvinyl alcohol composite and a preparation method thereof. As a small quantity of melanin is adopted to modify polyvinyl alcohol, the thermal decomposition temperature of polyvinyl alcohol can be substantially increased, simultaneously, the melting point of the polyvinyl alcohol can be reduced, and a wider melt processing window can be obtained. As a small quantity of modifying agent is added, the reduction of combination properties (rigidity, strength and barrier property) of the PVA (Polyvinyl Alcohol) caused by the addition of plenty of plasticizer is avoided, the pollution of packing materials caused by the migration of a micromolecule plasticizer is also avoided. The preparation method of the polyvinyl alcohol composite is simple and practicable and is easy for producing the polyvinyl alcohol composite.

Description

A thermoplastically processable polyvinyl alcohol composition and its preparation method

technical field

The invention relates to a polyvinyl alcohol composition capable of thermoplastic processing and a preparation method thereof. The composition is used for film products, such as single-layer film, multi-layer co-extruded film, biaxially stretched film, heat-shrinkable film, various hollow Containers, such as automobile fuel tanks, bottles, barrels, etc., various types of pipes, such as fuel or oil pipelines, and high barrier products such as various sheets.

Background technique

Polyvinyl alcohol (PVA) is a high-molecular polymer with excellent comprehensive properties that can be produced on a large scale by non-petroleum routes. It has excellent oil resistance, solvent resistance and gas barrier properties. It is used in packaging and transportation of hydrocarbon solvents, pesticides, petroleum, etc. Has unique advantages. Since a large number of intramolecular and intermolecular hydrogen bonds are easily formed between the adjacent hydroxyl groups of the PVA polymer chain, its thermal decomposition temperature (200-250°C) is close to the melting point (226°C), and it decomposes when it melts, making it difficult for thermoplastic processing. At present, the application of PVA is based on solution processing and forming. It is difficult to prepare three-dimensional products with thick walls and complex shapes through wet spinning and casting to prepare low-dimensional products such as fibers and films or as auxiliary materials. The application and development of PVA.

At present, for PVA melt processing technology, JP77110782A has reported a kind of film-forming method of melt blowing polyvinyl alcohol, and its technology adopts a large amount of water (content greater than 40%) as plasticizer, to reduce the melting point of PVA, make it in low Blow molding is realized at the decomposition temperature of PVA. However, this preparation method has poor stability in actual production. Due to the presence of a large amount of water, the resin is prone to foaming during extrusion, resulting in the inability to uniformly form the film.

And CN1368515 discloses a kind of novel speed-increasing method that is used for thermoplastic processing polyvinyl alcohol film, and this method mainly selects a kind of polymerizable amides monomer as plasticizer, and controls water to be more in resin to bind water The form exists, thereby effectively reducing the processing temperature of PVA resin, but the plasticizer selected by this method has certain toxicity, so that the prepared film is not suitable for environmental protection and food packaging film.

To achieve polyvinyl alcohol melt processing, generally speaking, a large amount of plasticizer must be added to significantly reduce the melting point of PVA resin and improve fluidity. However, the addition of a large amount of plasticizer will cause the decline of PVA's comprehensive performance (rigidity, strength, barrier performance), and the plasticizer is easy to migrate and pollute the packaging. Therefore, the most promising method is to add a small amount of additives to realize the thermoplastic processing of PVA.

Recently, Macromolecules, 20 11, 44, 9499-9507: "Thermooxidative Stabilization of Polymers Using Natural and Synthetic Melanins" reported that melanin (Melanin) can be used as a high-efficiency thermal stabilizer of polymethyl methacrylate to greatly improve the thermal stability of polymers. Thermal decomposition temperature, a small amount (0.5-5wt%) of melanin can increase the thermal decomposition temperature of PMMA by 50-90°C. However, there has been no research on the use of melanin in polyethylene systems to improve the melt processability of polyvinyl alcohol.

Contents of the invention

Melanin is a biomacromolecule containing polyphenols and amino structures. It is widely found in animals and plants and plays an antioxidant role in the human body. It can quickly capture the alkyl radicals, alkoxyl radicals and Peroxide free radicals to prevent thermal oxidative degradation of polymers.

Based on the above reasons, the present inventor utilizes melanin to modify PVA, the melting point of the obtained PVA composite material decreases, the thermal decomposition temperature increases, and a wide melting processing window is obtained to realize melting processing. After the material is melt processed, the amount of melanin added is small, Moreover, melanin belongs to biological macromolecules and is non-toxic, and the obtained polyvinyl alcohol composition has excellent comprehensive properties.

The purpose of the present invention is to provide a thermoplastically processable polyvinyl alcohol composition, which contains a small amount of melanin and has excellent comprehensive properties.

Another object of the present invention is to provide a method for the preparation of the composition.

A kind of polyvinyl alcohol composition of the present invention is characterized in that the following components of this composition compound: polyvinyl alcohol, melanin, polyvinyl alcohol: the weight ratio between melanin is (85～99.8): (15～0.2) .

The polyvinyl alcohol in the present invention is characterized in that the degree of polymerization of the polyvinyl alcohol is 1700-2400, and the degree of alcoholysis is 92-100%.

The melanin in the present invention includes various types of naturally extracted melanin disclosed in the prior art, and melanoids prepared by chemical synthesis and biological fermentation.

A preparation method of a polyvinyl alcohol composition in the present invention is characterized in that it is prepared by a method comprising one of the following steps:

(a) Add polyvinyl alcohol and melanin into the mixer in a certain proportion, mix thoroughly and evenly, then put the obtained premix into a twin-screw extruder, control the processing temperature at 170-250°C, and melt, plasticize and granulate .

(b) Put polyvinyl alcohol into distilled water to form a homogeneous solution, then add melanin and alkaline substances in a certain weight ratio, stir and mix evenly, and dry to obtain a polyvinyl alcohol composition.

The above-mentioned polyvinyl alcohol composition can utilize various single-layer or multi-layer extrusion processing equipment that can be thermoplastically processed to produce various films containing the composition, including: single-layer film, multi-layer co-organic film, Biaxially stretched film, heat-shrinkable film; hollow containers, including: automotive fuel tanks, bottles, barrels; various types of pipes, including fuel or oil pipelines, various sheets, and other high-barrier products made of this material.

Beneficial effects of the present invention:

(1) The present invention adds a small amount of melanin, increases the thermal decomposition temperature of polyvinyl alcohol and reduces the melting point of polyvinyl alcohol at the same time, obtains wider melt processing window and realizes thermoplastic processing;

(2) Because the amount of melanin added is small, and melanin belongs to biological macromolecules, it has the following advantages: on the one hand, the prepared polyvinyl alcohol composition is environmentally friendly and non-toxic, and the auxiliary agent is not easy to separate out, so it can be used in various products; On the one hand, melanin has little effect on the comprehensive properties of polyvinyl alcohol, and the tensile properties remain at a high level;

(3) The method is simple, feasible and easy to operate.

Detailed ways

Further describe the present invention below in conjunction with embodiment, the scope of the present invention is not limited by these embodiment. The scope of the present invention is set forth in the claims.

Example 1

Weigh 99.5g of polyvinyl alcohol (Sinopec Sichuan Vinylon Factory, brand 1799) and 900g of distilled water to dissolve under heating at 95°C, then add 0.5g of melanin into the solution and stir to mix evenly, then pour the mixed solution into a container, The samples were obtained by vacuum drying at ℃, and the standard specimens were prepared by hot pressing. The tensile properties were tested according to the GB-13022 standard. The thermal decomposition temperature and melting point were tested by a thermogravimetric analyzer and a differential scanning calorimeter.

The tensile strength of the obtained film was 60 MPa, the elongation at break was 267%, the thermal decomposition temperature was 255°C, and the melting point was 226°C.

Example 2

Weigh 95g of polyvinyl alcohol (Sinopec Sichuan Vinylon Factory, brand 1799) and 900g of distilled water to dissolve under heating at 95°C, then add 5g of melanin (self-made) into the solution and stir to mix evenly, then pour the mixed solution into a container, Vacuum-dried at 60°C to obtain samples, and then hot-pressed to prepare standard specimens. The tensile properties were tested according to the GB-13022 standard. The thermal decomposition temperature and melting point were tested by thermogravimetric analyzer and differential scanning calorimeter.

The tensile strength of the obtained film was 56MPa, the elongation at break was 320%, the thermal decomposition temperature was 271°C, and the melting point was 212°C.

Example 3

Weigh 475g of polyvinyl alcohol (Sinopec Sichuan Vinylon Factory, brand 1799) and 25g of melanin into a mixer, mix well, and then put the premix into a twin-screw extruder with a screw temperature of 220-225°C. The screw speed is 100rpm, extruded and granulated, the standard sample is prepared by hot pressing, the tensile performance test is carried out according to the GB-13022 standard, and the thermal decomposition temperature and melting point are tested by a thermogravimetric analyzer and a differential scanning calorimeter. .

The tensile strength of the obtained film was 55 MPa, the elongation at break was 270%, the thermal decomposition temperature was 270°C, and the melting point was 211°C.

Example 4

Weigh 450g of polyvinyl alcohol (Sinopec Sichuan Vinylon Factory, brand 1799) and 50g of melanin into a mixer, mix well, and then put the premix into a twin-screw extruder with a screw temperature of 215-222°C. The screw speed is 100rpm, extruded and granulated, the standard sample is prepared by hot pressing, the tensile performance test is carried out according to the GB-13022 standard, and the thermal decomposition temperature and melting point are tested by a thermogravimetric analyzer and a differential scanning calorimeter. .

The tensile strength of the obtained film was 53 MPa, the elongation at break was 250%, the thermal decomposition temperature was 281°C, and the melting point was 205°C.

Comparative example 1:

Weigh 100g of polyvinyl alcohol (Sinopec Sichuan Vinylon Factory, brand 1799) and 900g of distilled water, heat and dissolve at 95°C, then pour the solution into a container, dry it in vacuum at 60°C to obtain a sample, and cut it to prepare a standard sample. The tensile performance test was carried out according to the GB-13022 standard, and the thermal decomposition temperature and melting point were tested by a thermogravimetric analyzer and a differential scanning calorimeter.

The tensile strength of the obtained film was 58MPa, the elongation at break was 312%, the thermal decomposition temperature was 233°C, and the melting point was 231°C.

Compared with Comparative Example 1, due to the addition of 0.5% melanin by weight in Example 1, the thermal decomposition temperature in Example 1 has increased by 22 ° C, and the melting point has decreased by 5 ° C. Moreover, the tensile strength and elongation at break Has not changed much. Compared with Comparative Example 1, due to the addition of 5% melanin by weight in Example 2, the thermal decomposition temperature in Example 2 increased by 38°C, the melting point decreased by 19°C, and the tensile strength and elongation at break changed not big. Compared with Comparative Example 1, the more melanin added in the embodiment, the more the thermal decomposition temperature increases, the more the melting point decreases, and the larger the difference between the thermal decomposition temperature and the melting point is, the more conducive to melting processing. At the same time, Its tensile properties did not change much and remained at a high level.

Claims (10)

1. A polyvinyl alcohol composition characterized by comprising polyvinyl alcohol and melanin. 2. Composition according to claim 1, characterized in that no plasticizer is present in the composition. 3. The polyvinyl alcohol composition according to claim 1, characterized in that the weight ratio between polyvinyl alcohol and melanin is: (85-99.8): (15-0.2). 4. The polyvinyl alcohol composition according to claim 1 or 3, characterized in that the degree of polymerization of the polyvinyl alcohol is 1700-2400, and the degree of alcoholysis is 92-100%. 5. The polyvinyl alcohol composition according to claim 1 or 3, characterized in that the melanin is selected from naturally extracted melanin, chemically synthesized and bio-fermented melanoids. 6. according to the preparation method of the polyvinyl alcohol composition described in any one of claim 1～5, it is characterized in that comprising the method of one of following steps: (a) polyvinyl alcohol and melanin are weighed according to the weight ratio described in claim 3, added in the mixer, fully mixed, then the gained premix is put into a twin-screw extruder, and the processing temperature is controlled at 170 ~250°C, melted and plasticized to granulate. (b) Put polyvinyl alcohol into distilled water and configure it into a homogeneous solution, then weigh melanin according to the weight ratio described in claim 3, add it to the polyvinyl alcohol solution, stir and mix evenly, and dry to obtain the polyvinyl alcohol composition . 7. The use of the polyvinyl alcohol composition according to any one of claims 1 to 5 to make various barrier products containing it. 8. The use of the polyvinyl alcohol composition according to claim 7, the barrier products are film products, hollow containers, pipes and sheets. 9. A barrier product formed from the polyvinyl alcohol composition according to any one of claims 1-5. 10. The barrier product of claim 9, which is a film product, a hollow container, a tube or a sheet.