Polyethylene terephthalate acid hydrolysis

Polyethylene terephthalate (PET) is one of the most important commercial thermoplastic polyesters, which has been on the market since 1977 and is widely used in both industrial and household applications. Under specific conditions, plastics can be converted into their primary components for use in other chemical processes by chemical recycling. PET is a thermoplastic, and so recycling by chemical methods, which converts it into primary components, can be achieved. This study examines the optimal routes of the existing chemical methods. For chemical recycling, acidic hydrolysis is used and PET is converted into terephthalic acid (TPA) and... 

Another important area of polymer modification with subcritical and supercritical water is the hydrolysis of polycondensation polymers such as polyethylene terephthalate (PET), polyurethanes, and nylons for conversion to their monomers [ 37]. Specifically, in supercritical water, 91 % monomer recovery (terephthalic acid) is achieved at 400 °C and 400 bar in less than 15min reaction times [38]. Studies of these reactions using a hydrothermal diamond anvil cell to follow the phase changes during the reaction of PET... 

Hydrolysis reactions have been widely reported in NCW for low-molecular-weight molecules as well as for polymeric materials. Mandoki reported a process for depoly-merizing condensation polymers using NCW without addition of bases or acids. More particularly, polyethylene terephthalate, polybutene terephthalate, nylon 6, and nylon 66 were hydrolytically depolymerized (Fig. 9.25). 

Ester groups occur in a wide range of polymers (e.g., polyethylene terephthalate) and in copolymers such as, for example, ethylene vinyl acetate. The classical chemical method for the determination of ester groups, namely, saponification, can be applied to some types of polymer. For example, copolymers of vinyl esters and esters of vinyl esters and esters of acrylic acid, can be saponified in a sealed tube with 2 M sodium hydroxide. The free acids from the vinyl esters were determined by potentiometric titration or gas chromatography. The alcohols formed by the hydrolysis of the acrylate esters were determined by gas chromatography. Vinyl acetate ethylene copolymers can be determined by saponification with 1 N ethanolic potassium hydroxide at 80 C for 3 hours and back titration with standard acid or by saponification with p-toluene sulfonic acid and back titration with standard acetic acid [49, 50]. 

Because of its aromatic character and the dense packing of its molecular chains -compared to other polyesters - polyethylene terephthalate is very resistant to water, acids and bases, so that hydrolysis of the ester bond is initiated only above 100°C (Figure 5.316). 

The rate of hydrolysis reactions depends both on the protons as well as on the concentration of absorbed water. There is a direct proportionality between the rate of hydrolysis and water concentration. Dry polyethylene terephthalate absorbs moisture very quickly, depending on exposure time, particle shape, crystallinity, and relative humidity. Analogous to low-molecular carbonic acid esters, hydrolysis in polyethylene terephthalate is an autocatalytic reaction as long as acids or bases do not catalyze reactions [969]. 

Understanding the polymerization process used to make a particular plastic gives insight into the nature of the plastic. For example, plastics made via condensation polymerization, in which water is released, can degrade when exposed to water at high temperatures. Polyesters such as polyethylene terephthalate (PET) can degrade by a process called hydrolysis when exposed to acidic, basic, or even some neutral environments, severing the polymer chains. 

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