Kinds Of Polyesters Research Articles

Hydrolysis of polyesters by lipases.

INCREASING public concern about the treatment of waste materials has stimulated the study of the biodegradation of synthetic polymers. Among synthetic polymers, aliphatic polyesters are generally known to be susceptible to biological attack1–5, but there are few reports of enzymes involved in their degradation. Bell et al.6 recently showed that the molecular weight of polycaprolactone (PCL) decreases on exposure to the acid protease from Rhizopus chinensis for 6–10 d (decreasing from 13,000 to 10,000). In addition, Tabushi et al.7 have found that polyesters composed of phenyllactic acid and lactic acid are hydrolysed by α-chymotrypsin. We showed previously that a polyester-degrading enzyme from Penicillium sp. strain 14-3, purified to a homogeneous state as exhibited by ultracentrifugal analysis and polyacrylamide gel electrophoresis, has properties resembling lipase8. It was not previously recognised that lipase acts on polyesters. We report here that several commercial lipases and an esterase also hydrolyse polyesters, and that Rh. delemar lipase is capable of hydrolysing various kinds of polyesters.

Experimental studies on the application of polyurethane as a pit and fissure sealant

Polyurethanes have been recognized as a resin having a characteristically rubbery elasticity. This study aimed to evaluate the possibilities for application of polyurethanes as pit and fissure sealants.Experiments were conducted on two-component polyurethane systems in which two components are mixed together immediately before use. MDI (Diphenylmethanediisocyanate) was used as the isocyanate component, and three kinds of polyether and two kinds of polyester as the OH component.The tests for prepared polyurethanes were performed on (1) water absorption, (2) hardness, and (3) tensile strength. The tensile strength on bovine enamel etched with 3M phosphoric acid for 30 sec. was tested after curing the samples at room temperature for 3 days and immersing them in tap water at 37°C for a week. Bubble formation and marginal leakage were also tested. The bubble formation was examined on the etched occlusal surface of human molar teeth. In order to evaluate marginal leakage, penetration of fucsin dye was observed after thermal shock treatment (4°C-60°C) for 3 hrs. followed by the immersion in 0.2% fucsin solution for 24 hrs.The results obtained in this study were as follows:1) Water absorption during 5 days was approximately 1-3mg/cm2. It was found that the water absorption of polyester-polyurethanes was less than that of polyether-polyurethanes.2) The hardness value of the material, even that of the material which had the highest hardness among the five kinds of polyurethanes prepared, was only about half that of bis-GMA pit and fissure sealant (Nuva seal).3) The highest values of tensile strength were obtained at NCO/OH molar ratios of 8/1 and 10/1 in the polyether-polyurethanes, and a ratio of 3/1 in the polyester-polyurethanes.4) Bubble formation of polyurethanes which occurrs during the curring reaction was minimized by using 30%-50% solids (w/w) in ethyl acetate, since this material could be applied as a very thin film because of its low viscosity and consequently, carbon dioxide gas from the curing reaction could be discharged easily.5) Using 50% solids in the solvent at an NCO/OH molar ratio of 1/1, the marginal leakage after thermal shock was scarcely noticeable when using MDI/Castor oil of polyester-polyurethane, in contrast to the results obtained with polyether-polyurethane.6) Using the materials prepared at the NCO/OH molar ratios which showed the maximal tensile strength, marginal leakages after thermal schock were less in the case of the two kinds of polyester-polyurethane consisting of 50% solids in the solvent than in the three kinds of polyether-polyurethane.7) It is suggested that the material consisting of MDI/Castor oil is promising as a pit and fissure sealant in the two component polyurethane systems.

The determination of randomness in copolyesters by high resolution nuclear magnetic resonance

AbstractHigh‐resolution nuclear magnetic resonance (NMR) spectra of several kinds of polyesters were measured. Proton signals due to heterolinkages could be observed in some copolyesters, and the average sequence length and the degree of randomness in the copolyester were calculated from the intensities of their signals. A process in the transesterification reaction between two kinds of homopolyester was pursued with the NMR spectra. Random copolyester is formed by the ordinary molten‐state copolycondensation and also during the transesterification reaction between two kinds of homopolyester.