Degradation of Pure Aromatic Polyesters

Polyesters which solely contain aromatic acid components such as PET or PBT are commodity materials for many technical applications and are commonly regarded as quite resistant to any hydrol)n ic degradation. Only by applying very drastic chemical treatments, (e.g., sulfuric acid at 150 °C), which are a long way away from any physiological conditions, hydrolysis of such polymers can be achieved at reasonable rates, which can be used for recycling purposes [32]. Furthermore, chemical hydrolysis was applied in some cases for the analysis of aromatic polyesters [33]. 

From the point of view of the durability of aromatic polyesters investigations were performed to predict the life time of products in different environments. From a kinetic model, based on accelerated degradation experiments, some authors tried to characterise the long term behaviour of PET under ambient conditions [34, 35]. As one result the life 

In both cases hydrolytic degradation of PET was performed without any enzymic catalysis. Up to now there are no reliable indications available in the literature that microbes and enzymes can attack aromatic polyesters such as PET, PBT or poly(ethylene naphthalate) [2,41,42]. 

From all the information in the literature it can be concluded that conventional aromatic polyesters used up to now for technical purposes are not subject to a biologically induced degradation at a reasonable degradation rate. This excludes such polyesters from applications in biological waste treatment processes (composting) or which use biodegradability as a new material property for novel polymer applications, (e.g., controlled release of active substances in agriculture). 

However, recently a laid open specification of a German patent was published (DE 199 35 156 Al, 2000 [43]) where the inventors claim a procedure to disintegrate aromatic polyesters by means of special microbial strains Trichosporum and Arthrobacter). The deterioration of the test specimen took place over some weeks. Because of the limited information given in this application concerning the polymeric test material and the behaviour of the samples without contact to the microbes (blank tests) it is not clear if the claimed effects are really related to an enzymic action of the microorganisms involved. 

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