Research methods and development of PVA modificati

2022-09-22
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Research methods and development of PVA modification of thin films

[Abstract] this paper introduces the research status and development trend of PVA modification of thin films at home and abroad, as well as the main methods of PVA modification, and points out the practical significance of developing various PVA for thin films

key words: barrier; Water instant; biodegradation; Modified

polyvinyl alcohol (PVA) is a polymer containing a large number of hydroxyl groups, and its structural formula is: (ch2choh) n. Due to the small volume of its side groups - H and - Oh, it can enter the crystallization point without causing stress, so it has high crystallinity, which makes the permeability of PVA very small. At the same time, PVA has high water absorption due to the existence of - OH group. PVA is a water-soluble polymer with excellent properties and wide applications. The film prepared by it has excellent oxygen resistance, oil resistance, wear resistance, tear resistance, transparency, antistatic, printability, chemical corrosion resistance, etc. under certain conditions, it has water solubility and biodegradability, and occupies a unique and very important position in film materials. At present, the work of film modification with polyvinyl alcohol mainly focuses on the following aspects: modification of thermoplastic barrier packaging film, modification of water-soluble packaging film, and modification of biodegradable film

1 research status and progress of PVA modification of film

1.1 modification of thermoplastic barrier packaging film with PVA

pva is a high barrier material, but it contains a large number of hydroxyl groups, can form a large number of intramolecular and intermolecular hydrogen bonds, and its melting temperature is very close to the decomposition temperature, so it is difficult to thermoplastic processing. At present, most of the PVA films sold in the market are produced by tape casting, but the production cycle of tape casting is long, the efficiency is low, the film thickness, the quality is unstable, the labor intensity of workers is high, and the cost is high, which limits the popularization and application of PVA films. Therefore, modifying PVA so that the melting point of PVA is lower than its decomposition temperature and realizing the thermoplastic processing of PVA into film has great economic and social benefits. In this regard, a lot of human and material resources have been invested at home and abroad, and some progress has been made. The key point is to add a large amount of water as plasticizer to reduce the melting point of PVA and make it lower than the decomposition temperature of PVA, so as to realize PVA blow molding film. However, these methods and processes are complex and require high quality of instruments, equipment and operators, and have not yet achieved industrial production

in recent years, the methods used to improve the thermoplastic processability of PVA at home and abroad include: 1) adding small molecular substances such as glycerol, ethylene glycol and water for plasticization, but these small molecules are easy to precipitate out of the surface of the product in long-term use, affecting the performance of the product, so they are rarely used; 2) Add monomer in-situ polymerization (such as nylon monomer) to form a polymer with complementary structure with PVA or supplemented by a small amount of polar small Honeywell. The number of employees in China is about 12000 molecular substances, which are evenly dispersed in the PVA system and form hydrogen bonds, disrupting the regular arrangement of PVA molecules and reducing their crystallinity and melting point; 3) Copolymerization with other monomers, such as ethylene vinyl alcohol (EVOH); 4) Control the molecular weight and alcoholysis degree. The smaller the molecular weight and the lower the alcoholysis degree, the lower the melting temperature

domestic research in this area mainly includes the Institute of polymers of Sichuan University, the Institute of light industrial plastics processing and application, and the Department of materials science and engineering of Beijing Industrial and Commercial University. Among them, Wang Qi from the Polymer Research Institute of Sichuan University and others limited the crystallization of PVA, reduced the melting point of PVA and increased its heat by preparing polymers and plasticizers with complementary structures with PVA. Please re tension the tensioning wheel; Stability, which can realize the thermoplastic processing of PVA. The general process route is as follows: 1) dissolve 5-45 parts of polymerizable monomers (by weight) of starting materials in 5-40 parts of water to prepare a solution with a certain concentration, then add 0.1-20 parts of additives after auxiliary chewing, and stir to form a uniform solution; 2) Swell PVA (polymerization degree 500~2000, alcoholysis degree 87%~100%) parts of the above solution at 150 ℃; 3) Conduct thermoplastic processing on PVA with good swelling, the temperature is 80~190 ℃, and the melting time before molding is 0.2~20min; 4) Heat treat the thermoplastic molding material at 100~200 ℃ for 5~30min. It is found that the addition of modifier greatly improves the thermoplastic processability of PVA, which can be hot pressed at 140 ℃, and the film has good uniformity, small thickness, high strength, good flexibility and high transparency. The plasticizing temperature of PVA was reduced by adding alcohol amine plasticizing modifier to the Institute of light industrial plastics processing and application and Xiang Aimin, Department of materials science and engineering, Beijing University of technology and technology. The process route is as follows:

it is found that under the same dosage of plasticizing modifier, the plasticizing temperature increases with the increase of the relative molecular weight of PVA. See Table 1 for specific data

with the increase of alcoholysis degree, the plasticizing property of PVA decreases. See Table 2 for the relationship between plasticizing property and alcoholysis degree

low polar molecules such as water are easy to insert into PVA to modify it, but due to the low boiling point of water, it is easy to bubble during molding, making the processing process difficult to stabilize; The oligomer has large relative molecular weight and high boiling point, and takes a long time to interact with it. It is easy to make PVA oxidize and turn yellow at high temperature, and the melt strength decreases, which cannot meet the processing performance requirements. Alcohol amine compound modifier can plasticize and extrude PVA at appropriate temperature, and realize PVA dry extrusion granulation and film blowing. With the increase of modification dose, the melting temperature decreases greatly and the melt fluidity increases. When the dosage of modifier continues to increase, the decrease of melting temperature slows down

foreign research in this area has also made great progress. Japan synthetic chemical company has recently developed ユコマテイイイイイイユコマテイイaxpva copolymer film, which has excellent molding performance, melting point between 200~210, molding processing temperature in the range of 210~230 ℃, and its thermoplastic processability is achieved by copolymerization with other monomers. The setting of the PVA recovery system of Kuraray poval CP series developed in the United States is to restore the original setting of the computer before exiting the utilization program. The resin has good thermoplastic processing performance and can be melt processed at about 170 ℃. It is reported that its thermoplastic and water solubility are obtained by controlling the degree of polymerization and alcoholysis of PVA. (to be continued)

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