As we all know, plastic has become an important material for the packaging industry. Plastics have brought great pressure on the ecological environment while enriching and facilitating people's lives. Recycling and using packaging wastes and protecting the ecological environment are imminent. In the packaging waste, waste polyester occupies a considerable proportion, it is easy to identify recycling, and has the value of industrial use. In this paper, through the chemical alcoholysis method, the waste polyester or alcohol is decomposed into terephthalic acid diol ester (abbreviated as diol ester), used in the synthesis of unsaturated polyester resin, giving the resin product superior performance, turning waste For Treasure, it provides an effective way for industrialization to use waste polyester.
First, the feasibility of waste polyester alcoholysis process (a) the principle of alcoholysis In the chemical synthesis of industrial polyester, terephthalic acid diethylene glycol under the appropriate conditions for polycondensation reaction to generate polyester and ethylene glycol, The reaction was carried out continuously by removing ethylene glycol by decompression, and the molecular weight of polyester was continuously increased until a predetermined value range. Therefore, in the presence of high temperatures and catalysts, high molecular weight polyesters can be degraded with ethylene glycol (or other glycol) to achieve its reverse reaction to produce glycol esters with hydroxyl groups at both ends. This glycol ester is no longer a mere product, but a mixture of terephthalic acid diethylene glycol condensates with different degrees of polymerization. The mixture has an average degree of polymerization and indicates the average number of repeat units "ethylene terephthalate" in the product molecule. The smaller the average degree of polymerization, the better the degree of alcoholysis.
(II) Alcoholysis conditions and process flow A certain amount of waste polyester chips and dihydric alcohols are put into the alcoholysis apparatus, and an appropriate amount of modifiers and catalysts are added, and heated to 180 degrees--230 degrees for alcoholysis. Samples were taken after hours to confirm that the alcoholysis reaction was complete, post-treatment 1, after the temperature was lowered, directly used for the synthesis of unsaturated polyester; 2. After the temperature was lowered, a dispersant was added. After standing and layering and filtering, a higher purity glycol ester is obtained, which is used for the synthesis of polyurethane, insulating paint, hot melt adhesive and the like.
(C) the main factors affecting the alcoholysis process 1. Alcoholysis temperature The alcoholysis reaction causes the polymer chain to decompose and require heat absorption, which is required to be performed at high temperatures. In the early stage of alcoholysis, the warming is beneficial to the softening and melting of the waste polyester in the glycol. The rate of the alcoholysis reaction increases with increasing temperature. When the temperature exceeds 230 degrees, the oxidation color of the reaction system will be darkened, which will affect the later application. Therefore, the reaction temperature should be controlled below 230 degrees; at the same time, the alcoholysis temperature exceeds the The boiling point of the glycol should be used to prevent the glycol from evaporating and losing, in order to facilitate the alcoholysis reaction.
2, after a series of experimental studies found that the alcoholysis reaction factors have the following relationship: k = 1 / (am-1) or m = 1 / a (1/k + 1) where: k is the equilibrium constant of the alcoholysis reaction, It is related to the reaction temperature and reaction pressure; m is the average degree of polymerization of alcoholysis products, and the degree of alcoholysis is characterized; a is the excess ratio of glycol, the number of glycols and the ethylene terephthalate in waste polyester. "The number of repeat units is the number of pens.
When the reaction conditions (temperature, pressure) are determined, the reaction equilibrium constant k remains basically unchanged. Therefore, the degree of alcoholysis is only related to the excess glycol coefficient. By varying the glycol excess coefficient, the degree of polymerization m of the alcoholysis product is substantially inversely related to the glycol excess coefficient a.
The hydroxyl content of the product was determined by the hydroxyacetylation method and the m value was calculated from the product formula. The m value is between 1 and 2, indicating that the alcoholysis product is mainly a mixture of ethylene terephthalate having a degree of polymerization of 1 and a degree of polymerization of 2. As the value of a increases, the hydroxyl content of the resulting alcoholylated product also increases, so that the average degree of polymerization decreases and the extent of alcoholysis tends to be complete. When the value of a is 1.2--1.4, the am value is the smallest, and the effect of alcoholysis is best.
The above analysis shows that adjusting the amount of glycol, by measuring the hydroxyl content of the sample during alcoholysis, can achieve the purpose of controlling the degree of alcoholysis.
2. Synthesis of Unsaturated Polyester Resins (I) Selection of Diols Typical unsaturated polyester resins are polycondensed with unsaturated dibasic acids, saturated dibasic acids, and diols, followed by polymerizable monomers (generally Made of styrene) mix. Glycol esters used in the synthesis of unsaturated polyesters use glycol esters instead of saturated dibasic acids and glycols. The resulting unsaturated polyester has good miscibility with styrene and gives the resin a good curing property (hardness, thermal deformation). The performance of these properties is related to the nature of glycol esters. By using different glycols to alcoholize waste polyol esters, the resulting glycol esters exhibit different properties when used to synthesize unsaturated polyesters. The alcoholysis products of the dihydric alcohols with longer carbon chains (carbon atoms greater than 3) are not easy to crystallize, and generally are in the form of pastes. The unsaturated polyesters synthesized have great flexibility and good miscibility with styrene, but The hardness of the resin after curing is small and the thermal deformation is poor; while the short-chain diol can keep the resin rigid. Therefore, ethylene glycol and propylene glycol are mainly used for experiments and applications. Due to the symmetry of the glycol-based polyester molecules, it shows a strong crystallization tendency, and it is mixed and delaminated with styrene, and it is necessary to introduce modifiers to destroy the symmetry of the unsaturated polyester and reduce the crystallization tendency. Miscibility with styrene.
(B) Effect of Modifier In the polycondensation reaction of unsaturated polyester, the excess coefficient of glycol is usually between 1.05 and 1.15 in order to control the molecular weight of the polycondensate. The use of glycol esters in place of saturated dibasic acids and glycols involved in the polycondensation reaction also considered the molecular weight control of unsaturated polyesters. In the alcoholysis of waste polyester, the excess glycol coefficient is as high as 1.2-1.4. If this alcoholysis product is directly used in unsaturated polyester synthesis without treatment, it obviously does not meet the process requirements. If the alcoholysis product is processed, Removing excess glycol can increase production costs. However, simply reducing the amount of glycol, the degree of alcoholysis will decrease, and the degree of polymerization of glycol esters will increase, which will affect the miscibility of synthetic polyesters with styrene. In this way, the glycol excess coefficient can be moderately reduced to meet the synthesis process and production cost requirements. Experiments show that: by adding modifiers to reduce the glycol excess coefficient to 1.1, the resulting glycol esters can be directly used to synthesize unsaturated polyesters, polyesters and styrene have good miscibility, the hardness of the resin after curing Large, high heat distortion temperature.
(3) Performance parameters and application performance of synthetic polyester resins Through the selection of diols, it was determined that ethylene glycol plus modifiers and propylene glycol plus modifiers were used to alcoholize waste polyesters to obtain ethylene glycol type II. E-PET and P-PET, respectively, with unsaturated dicarboxylic anhydrides (maleic anhydride) to synthesize unsaturated polyesters to give unsaturated polyester resins 9199(E) and 9199 (P).
The prepared 9199(E) and 9199(P) resins were made into castings and glass steel products respectively, and the Barcol hardness, heat distortion temperature and bending strength of the glass fiber were measured and compared with the national standard. By comparison, 9199 (E), 9199 (P) performance indicators are better than general-purpose resin, except for the 9199 (P) Brinell hardness slightly lacking, other indicators have reached the heat-resistant resin index.
Third, the application prospect Unsaturated polyester resin is a multi-model engineering materials, its production process is mature and stable, easy to operate, the product is widely used in the production of glass steel products, casting products, artificial marble, decorative panels, etc., involving transportation, aerospace , electromechanical, construction, petroleum, and chemical industries. At present, China's output exceeds 100,000 tons, most of which are general-purpose resins. To produce heat-resistant, corrosion-resistant, high-electricity resins, it is necessary to use more expensive raw materials for modification, and the cost of resin production is higher. The use of waste polyester to produce unsaturated polyester resin, due to the introduction of terephthalic acid groups to improve the regularity of the molecular chain, so that the resin heat resistance, physical and mechanical strength, chemical resistance and electrical properties have significantly improved and improve. It can be said that with cheap raw materials, excellent products have been obtained. In addition, in industrial production, it is difficult to synthesize terephthalic acid directly using terephthalic acid to produce styrenic unsaturated polyester, while the use of alcoholysis product terephthalic acid diol ester to synthesize unsaturated polyester resin is a process for producing benzene-type resin. On the break. It can be considered as an economical, practical, and effective process route with broad prospects. It is also an important way for domestic recycling of waste polyester.
First, the feasibility of waste polyester alcoholysis process (a) the principle of alcoholysis In the chemical synthesis of industrial polyester, terephthalic acid diethylene glycol under the appropriate conditions for polycondensation reaction to generate polyester and ethylene glycol, The reaction was carried out continuously by removing ethylene glycol by decompression, and the molecular weight of polyester was continuously increased until a predetermined value range. Therefore, in the presence of high temperatures and catalysts, high molecular weight polyesters can be degraded with ethylene glycol (or other glycol) to achieve its reverse reaction to produce glycol esters with hydroxyl groups at both ends. This glycol ester is no longer a mere product, but a mixture of terephthalic acid diethylene glycol condensates with different degrees of polymerization. The mixture has an average degree of polymerization and indicates the average number of repeat units "ethylene terephthalate" in the product molecule. The smaller the average degree of polymerization, the better the degree of alcoholysis.
(II) Alcoholysis conditions and process flow A certain amount of waste polyester chips and dihydric alcohols are put into the alcoholysis apparatus, and an appropriate amount of modifiers and catalysts are added, and heated to 180 degrees--230 degrees for alcoholysis. Samples were taken after hours to confirm that the alcoholysis reaction was complete, post-treatment 1, after the temperature was lowered, directly used for the synthesis of unsaturated polyester; 2. After the temperature was lowered, a dispersant was added. After standing and layering and filtering, a higher purity glycol ester is obtained, which is used for the synthesis of polyurethane, insulating paint, hot melt adhesive and the like.
(C) the main factors affecting the alcoholysis process 1. Alcoholysis temperature The alcoholysis reaction causes the polymer chain to decompose and require heat absorption, which is required to be performed at high temperatures. In the early stage of alcoholysis, the warming is beneficial to the softening and melting of the waste polyester in the glycol. The rate of the alcoholysis reaction increases with increasing temperature. When the temperature exceeds 230 degrees, the oxidation color of the reaction system will be darkened, which will affect the later application. Therefore, the reaction temperature should be controlled below 230 degrees; at the same time, the alcoholysis temperature exceeds the The boiling point of the glycol should be used to prevent the glycol from evaporating and losing, in order to facilitate the alcoholysis reaction.
2, after a series of experimental studies found that the alcoholysis reaction factors have the following relationship: k = 1 / (am-1) or m = 1 / a (1/k + 1) where: k is the equilibrium constant of the alcoholysis reaction, It is related to the reaction temperature and reaction pressure; m is the average degree of polymerization of alcoholysis products, and the degree of alcoholysis is characterized; a is the excess ratio of glycol, the number of glycols and the ethylene terephthalate in waste polyester. "The number of repeat units is the number of pens.
When the reaction conditions (temperature, pressure) are determined, the reaction equilibrium constant k remains basically unchanged. Therefore, the degree of alcoholysis is only related to the excess glycol coefficient. By varying the glycol excess coefficient, the degree of polymerization m of the alcoholysis product is substantially inversely related to the glycol excess coefficient a.
The hydroxyl content of the product was determined by the hydroxyacetylation method and the m value was calculated from the product formula. The m value is between 1 and 2, indicating that the alcoholysis product is mainly a mixture of ethylene terephthalate having a degree of polymerization of 1 and a degree of polymerization of 2. As the value of a increases, the hydroxyl content of the resulting alcoholylated product also increases, so that the average degree of polymerization decreases and the extent of alcoholysis tends to be complete. When the value of a is 1.2--1.4, the am value is the smallest, and the effect of alcoholysis is best.
The above analysis shows that adjusting the amount of glycol, by measuring the hydroxyl content of the sample during alcoholysis, can achieve the purpose of controlling the degree of alcoholysis.
2. Synthesis of Unsaturated Polyester Resins (I) Selection of Diols Typical unsaturated polyester resins are polycondensed with unsaturated dibasic acids, saturated dibasic acids, and diols, followed by polymerizable monomers (generally Made of styrene) mix. Glycol esters used in the synthesis of unsaturated polyesters use glycol esters instead of saturated dibasic acids and glycols. The resulting unsaturated polyester has good miscibility with styrene and gives the resin a good curing property (hardness, thermal deformation). The performance of these properties is related to the nature of glycol esters. By using different glycols to alcoholize waste polyol esters, the resulting glycol esters exhibit different properties when used to synthesize unsaturated polyesters. The alcoholysis products of the dihydric alcohols with longer carbon chains (carbon atoms greater than 3) are not easy to crystallize, and generally are in the form of pastes. The unsaturated polyesters synthesized have great flexibility and good miscibility with styrene, but The hardness of the resin after curing is small and the thermal deformation is poor; while the short-chain diol can keep the resin rigid. Therefore, ethylene glycol and propylene glycol are mainly used for experiments and applications. Due to the symmetry of the glycol-based polyester molecules, it shows a strong crystallization tendency, and it is mixed and delaminated with styrene, and it is necessary to introduce modifiers to destroy the symmetry of the unsaturated polyester and reduce the crystallization tendency. Miscibility with styrene.
(B) Effect of Modifier In the polycondensation reaction of unsaturated polyester, the excess coefficient of glycol is usually between 1.05 and 1.15 in order to control the molecular weight of the polycondensate. The use of glycol esters in place of saturated dibasic acids and glycols involved in the polycondensation reaction also considered the molecular weight control of unsaturated polyesters. In the alcoholysis of waste polyester, the excess glycol coefficient is as high as 1.2-1.4. If this alcoholysis product is directly used in unsaturated polyester synthesis without treatment, it obviously does not meet the process requirements. If the alcoholysis product is processed, Removing excess glycol can increase production costs. However, simply reducing the amount of glycol, the degree of alcoholysis will decrease, and the degree of polymerization of glycol esters will increase, which will affect the miscibility of synthetic polyesters with styrene. In this way, the glycol excess coefficient can be moderately reduced to meet the synthesis process and production cost requirements. Experiments show that: by adding modifiers to reduce the glycol excess coefficient to 1.1, the resulting glycol esters can be directly used to synthesize unsaturated polyesters, polyesters and styrene have good miscibility, the hardness of the resin after curing Large, high heat distortion temperature.
(3) Performance parameters and application performance of synthetic polyester resins Through the selection of diols, it was determined that ethylene glycol plus modifiers and propylene glycol plus modifiers were used to alcoholize waste polyesters to obtain ethylene glycol type II. E-PET and P-PET, respectively, with unsaturated dicarboxylic anhydrides (maleic anhydride) to synthesize unsaturated polyesters to give unsaturated polyester resins 9199(E) and 9199 (P).
The prepared 9199(E) and 9199(P) resins were made into castings and glass steel products respectively, and the Barcol hardness, heat distortion temperature and bending strength of the glass fiber were measured and compared with the national standard. By comparison, 9199 (E), 9199 (P) performance indicators are better than general-purpose resin, except for the 9199 (P) Brinell hardness slightly lacking, other indicators have reached the heat-resistant resin index.
Third, the application prospect Unsaturated polyester resin is a multi-model engineering materials, its production process is mature and stable, easy to operate, the product is widely used in the production of glass steel products, casting products, artificial marble, decorative panels, etc., involving transportation, aerospace , electromechanical, construction, petroleum, and chemical industries. At present, China's output exceeds 100,000 tons, most of which are general-purpose resins. To produce heat-resistant, corrosion-resistant, high-electricity resins, it is necessary to use more expensive raw materials for modification, and the cost of resin production is higher. The use of waste polyester to produce unsaturated polyester resin, due to the introduction of terephthalic acid groups to improve the regularity of the molecular chain, so that the resin heat resistance, physical and mechanical strength, chemical resistance and electrical properties have significantly improved and improve. It can be said that with cheap raw materials, excellent products have been obtained. In addition, in industrial production, it is difficult to synthesize terephthalic acid directly using terephthalic acid to produce styrenic unsaturated polyester, while the use of alcoholysis product terephthalic acid diol ester to synthesize unsaturated polyester resin is a process for producing benzene-type resin. On the break. It can be considered as an economical, practical, and effective process route with broad prospects. It is also an important way for domestic recycling of waste polyester.
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