The present article describes synthesis and degradability of a series of polyesters having tetrahydropyran or tetrahydrofuran rings in their main chains. Most of these polyesters were prepared by ring-opening polymerization of bicyclic oxa1actones and the rest were prepared by polycondensation of the corresponding hydroxy carboxylic acids. Spontaneous hydrolysis of these polyesters was examined in a neutral phosphate buffer solution at ambient temperature. Polyesters of an ether-ester type with tetrahydropyran rings in the backbones were hardly hydrolyzed, whereas polyesters of an ether-ester type with tetrahydrofuran rings in the backbones were hydrolyzed, although very gradually. In contrast, polyesters of acetal-ester types with tetrahydropyran rings in the main chains were re1atively easily hydrolyzed, eventually giving the corresponding hydroxytetrahydropyran carboxylic acids. The hydrolysis rates were varied depending on the linkage-modes comecting tetrahydropyran rings, besides the hydrophilicity or hydrophobicity of the pendant groups. Biodegradability of these polyesters was assessed by degradation tests both in soil and in an activated sludge. Polyesters of acetal-ester types were degraded in soil as well as in the activated sludge. Quantitative determination of carbon dioxide evolved during the treatment of the hydrolysates in the activated sludge showed that the polyesters with out pendant alkoxycarbonyl groups were biodegradable and that the polyester having 2, 6-linked tetrahydropyran rings in the backbone was most readily susceptible to biodegradation.

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Enzymatic degradations of microbial and synthetic polyesters were investigated at 37°C in an aqueous solution (pH 7.4) containing 23 kinds of commercial lipases. Five types of aliphatic polyesters, poly [ (R) -3-hydroxybutyrate) ]: P [ (R) -3HB], poly (3-hydroxypropionate) : P (3HP), poly (4-hydroxybutyrate): P (4HB), poly (5-hydroxyvalerate): P (5HV), and poly (6-hydroxyhexanoate): P (6HH), were used. All lipases except for two types hydrolyzed P (3HP) films. However, no lipases eroded P [ (R) -3HB] films. The number of lipases capable of hydrolyzing respective polyesters decreased as the carbon number of monomeric units increased; P (3HP) >P (4HB) >P (5HV) >P (6HH). The substrate specificities of lipases for hydrolysis of polyesters have been discussed.

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The ring-opening copolymerization of succinic anhydride with various oxiranes by organometalic compounds (diethyl zinc, Al₂-Zn-μ-oxoalkoxide, and aluminium isopropoxide) and the biodegradability of the produced polymers were investigated. The initiator influenced the molecular weight and the composition of these copolymers. Random copolymers were produced by diethyl zinc. The molecular weight of these copolymers were larger than those of copolymers obtained using other initiators. Aluminium isopropoxide gave alternative copolymers of succinic anhydride with oxirane. The amount of initiator affected the molecular weight of these copolymers. The copolymers of succinic anhydride with ethylene oxide were crystalline, while the copolymers with propylene oxide were amorphous. The biodegradation values of the copolymers were evaluated by an enzymatic hydrolysis method. The aliphatic copolymers of succinic anhydride with ethylene oxide, propylene oxide or allyl glycydil ether were readily degraded by a lipase. However, the aromatic copolymers produced from succinic anhydride with styrene oxide or phenyl glycydil ether were little degraded. The degradation can be controlled by the ester content and molecular weight of these copolymers.

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Biodegradability of commercial flexible polyurethane foams and those containing Biopol was investigated by a soil burial method. The weight loss of the samples (5×5×1cm) was determined within 3% of analysis errors. The soilburial experiment was carried out at two different test fields (Byoho and Hakyuchi). Both the soils had greatly different degradation activities for degradation of ether-and ester-type polyurethane foams, and biodegradability of the ester-type foams was larger than that of ether-type foams. TR, JM and SG (polyurethane sample names shown in Table 1) degraded in soil up to 40-60% weight loss after 12 months, comparable to the value for Buna wood. Biodegradability of the polyurethane foam containing Biopol was dependent upon the chemical structure of the polyurethane except the degradation during the initial period (about 3 months), and the additional Biopol did not promote the biodegradation.

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In order to elucidate anaerobic biodegradation of poly (3-hydroxybutyrate) (PHB), the degradation in anaerobic enrichment cultures inoculated with many environmental samples and the distribution of PHB-degrading anaerobic bacteria were investigated. Strict anaerobic enrichment cultures containing fibrous PHB were inoculated with 102 samples which were collected from 17 sampling points of the southern part of Ibaraki prefecture and the northern part of Chiba prefecture. In 61 enrichment cultures, the fibrous PHBs were disintegrated into powder, and decreases in the powder volume were observed. Analysis of the residual PHB, culture broth, and gaseous components indicated that PHB was degraded by the anaerobic bacterial attack. The accumulation of some volatile fatty acids as main fermentation products suppressed the bacterial degradation. The PHB-degrading anaerobic bacteria distributed widely in environment, particularly, in anaerobic bottom sediments.

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Aliphatic copolyesterethers were synthesized from several cyclic esters with ethylene oxide or propylene oxide by ring-opening copolymerization. The biodegradability was estimated by hydrolysis using lipase (Rhizopus arrhizus) from the chemical structural point of view. The biodegradability was influenced by the polymer composition, substituted methyl group, methylene chain length, and hydrophilicity. The biodegradability has the maximum at a certain composition depending on the ester content, the randomization, and crystallinity. The methyl side group in the polymer chain suppresses the degradation. The copolymers having long methylene chains have high biodegradability because of flexibility of the polymer chain. Hydrophilicity promotes biodegradability. The hydrolyzed products were analyzed by ¹H NMR spectroscopy. The water-soluble fraction mainly contained ethylene glycol, its oligomers, ω-hydroxycarboxylic acids and polyethers having a carboxylic group at its end. The insoluble fraction consisted of degraded copolymers.

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Poly (γ-glutamic acid) (PGA) hydrogels have been prepared by means of γ-irradiation of PGA produced by Bacillus subtilis IF03335 in aqueous solutions. When a dosage of γ-irradiation was 2 Mrad or more and a concentration of PGA in water was 2wt% or more, transparent hydrogels could be produced. In the case of 2 Mrad of γ-irradiation and 5 wt% of PGA concentration, specific water content (wt of water/wt of polymer) of PGA hydrogel was approximately 3500. Specific water contents of PGA hydrogels decreased markedly with an increase in a dosage of γ-irradiation. Swelling equilibria of PGA hydrogels were measured in water or in aqueous solutions of various pH's or concentrations of NaCI or CaCl₂. Under acid conditions or on addition of electrolytes, degrees of swelling of PGA hydrogels were smaller than that in distilled water.

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As biodegradable high molecular weight polycarboxylates, polycarboxylate copolymers containing poly (vinyl alcohol) (PVA) blocks as biodegradable segments in the polymer chain were prepared and the relations between the PVA-block length as well as the chemical structure of the comonomers and their biodegradability were analyzed. It was confirmed that a certain chain length of the PVA-block was neccessary to be accepted as a substrate for PVA-degrading microbes to cleave the polymer chain, because the accessibility of the PVA-block was affected by both the neighboring functional groups and the steric and electrostatic effects caused by the entire copolymer chain. The extent of these effects varied depending on the molecular structure of the carboxylate comonomers. The minimum PVA-block length for the biodegradation segment was estimated to be 2-3 monomer units for the methylene malonate copolymers which might have expanded conformations in aqueous solutions. On the other hand, the minimum PVA-block length was estimated to be 6-7 and 8-10 monomer units for the fumarate copolymers and maleate copolymers, respectively, which might have less expanded coiled conformations in aqueous solutions.

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Biodegdable polymer “Mater-Bi”, a polymer alloy of starch and modified poly (vinyl alcohol), was examined. According to the biodegadability test equivalent to the ASTM method, “Mater-Bi” was as biodegradable as papers forshopping bags, and the degraded ratio was 91% after 313 days. Compostability of “Mater-Bi” was also measured according to the ASTM method. The results of physical, chemical, and biological tests of the compost obtained from “Mater-Bi” with garbage indicated that “Mater-Bi” was compostable. “Mater-Bi” is thusuilized in the form of compost after its duty.

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Biodegradability of polyethers and their derivatives was examined in the biodegradation by activated sludeges from muniipal sewage plants, growth of polyethylene glycol (PEG) -or polypropylene glycol (PPG) -utiliing bacteria and PEG dehydrogenase activities. Free terminal hydroxyl groups were necessary for biodegradation of polyethers. Chemical degradation of PEG by Fenton's reagent suggested endogenous breakdown of the molecule. On the contrary, biodegradation of PEG suggested that metabolism occurs exogenously at the end of the molecule. The maximum molecular weights which can be assimilated by bacteria were expected to be 20000-30000, but PEG dehydrogenase appreciably oxidized PEG 50000. This suggests that PEG with a molecular weight higher than 20000-30000 could be metabolized, but the rate was too slow to support the growth of bacteria. The cleavage of an ether bond seemed to occur between the ether oxygen and β-carbon from the starting point of biodegradation, because a PEG or PPG molecule depolymerized by one glycol unit is produced from carboxylated or carbonyl PEG or PPG.

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To evaluate the biodegradability of biodegradable plastics, a method of determining the amounts of ¹³CO₂ liberated from ¹³C-labeled plastics was developed. As biodegradable plastic, microbial polyester, poly (3-hydroxybutyrate) (PHB), was chosen. Using sodium acetate-1-¹³C as a carbon source, ¹³C-1-labeled PHB was prepared from Alcaligenes eutrophus cells. Carbon dioxide produced from a flask which contained soil and ¹³C-labeled PHB film (about 25cm2, 50mg) was fixed to calcium carbonate and purified in a special apparatus. The final sample of ^l3CO₂ was trapped in a cold finger and analyzed by GC-MS. The percentage of ¹³CO₂ increased to about 15% from the starting value (about 1%) in 15 days. This method has sufficiently high sensitivity and specificity.

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Copolyamide-esters (CPAE) were produced from lactones and ε-caprolactam by ring-opening copolymerization using Na catalyst under reduced pressure. The biodegradability was evaluated from the amount of water-soluble products determined with a TOC analyzer in enzymatic hydrolysis. The hydrolysis was carried out in a phosphate buffer solution at 30°C with Rhrizopus arrhizus lipase, and most of the copolymers were degradated. The degradability decreased with an increase in the T_m (melting points) of CPAE as a result of an increase in the amide bond contents.

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Enzymatic degradation of blend yarns of polycaprolactone (PCL) with low density polyethylene (LDPE) was investigated. PCL content necessary to make the blend yarns susceptible to enzymatic degradation decreased with increasing value of _ηLDPE/_ηPCL (_ηLDPE, melt viscosity of LDPE; _ηPCL, melt viscosity of PCL). PCL was thus assumed to form a continuous phase in the enzymatically degradable blends on the basis of the _ηLDPE/_ηPCL values and ø _PCLø _LDPE values (ø _PCL, volume fraction of PCL; ø _LDPE, volume fraction of LDPE).

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Poly (_L-lysine-sebacic acid) (PLS) and poly (_L-lysine-terephtalic acid) (PLP) were synthesized by the low temperature polycondensations of sebacoyl chloride or terephthaloyl chloride with N, N'-bis (trimethylyl) -_L-lysine-ethyl ester (TMSL), respectiveiy. Hydrolytic and enzymatic degradation of PLS and PLP films were investigated by the determination of the weight loss, mechanical properties of their films, and SEM. The rate of enzymatic degradations of PLS films were found to be much higher than those of its hydrolytic degradation. However, tke rate of enzymatic degradation of PLP films was the same as that of its hydrolytic degradation, and lower than that of PLS films. These results indicate that the aliphatic polyamide containing _L-lysine is a biodegradable polymer.

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Degradation rates of commercial biodegradable plastic “MATER-BI”, an interpenetrating network polymer of amylose or amylopectin and poly (vinyl alcohol), and poly (ε-caprolactone) (PCL) were determined. We found that photoirradiation test is useful for PCL and hydrolysis test for “MATER-BI”.

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