Mal-Nam Kim

Antimicrobial activity of phenol and benzoic acid derivatives

Vinyl monomers with phenol and benzoic acid as pendant groups were synthesized, and their antimicrobial activities were examined on equal weight basis using the halo zone test. For both bacteria and fungi, the halo zone diameter decreased in the order of p-hydroxyphenyl acrylate (M2) > allyl p-hydroxyphenyl acetate (M1) p-2-propenoxyphenol (M3). Polymerization of the monomers decreased their antimicrobial activity significantly, but the order of the halo zone diameter for the polymers was the same as that of the corresponding monomers. Glassy polymers exhibited low antimicrobial activity when compounded with low molecular weight antimicrobial agents due to the extremely slow diffusion. Antimicrobial polymers could find a successful application such as coating on glassy polymers, in spite of the lower antimicrobial activity compared to the respective monomers.

Diffusion coefficient and equilibrium solubility of water molecules in biodegradable polymers

The diffusion coefficient and solubility of water molecules were measured in polyglycolide (PGA), poly(L-lactide) (PLLA), poly[(R)-3-hydroxybutyrate] (PHB), poly(ϵ-caprolactone) (PCL), and SkygreenR (SG). The diffusion coefficient and equilibrium solubility decreased in the order SG > PCL > PLLA > PHB > PGA and PGA > SG > PLLA > PHB > PCL, respectively. The diffusion coefficient and solubility of water at low sorption temperature in PHB varied according to the initial crystallinity of the matrix polymer even though crystallization of PHB molecules took place during the sorption experiment. In contrast, the amorphous PLLA and the crystalline PLLA showed an almost identical diffusion coefficient and solubility of water, in spite of the fact that the amorphous PLLA remained practically amorphous during the whole sorption procedure. A strong correlation existed between the water solubility and the surface tension or contact angle of the polymer matrix. The water diffusivity in PGA was almost 2 orders of magnitude lower while water was more soluble in PGA with a lower heat of sorption than that corresponding to the other more hydrophobic polymers, indicating that the transport of water molecules in PGA followed the solution–diffusion model.

Biodegradation of poly(3-hydroxybutyrate), Sky-Green® and Mater-Bi® by fungi isolated from soils

In order to characterize the degradation behavior of three commercial biodegradable plastics, poly(3hydroxybutyrate) (PHB), Sky-Green 1 (SG), a biodegradable aliphatic polyester made of succinic acid, adipic acid, butanediol and ethylene glycol, and Mater-Bi 1 (MB), a composite composed of starch based biodegradable polymers, were incubated in the forest soil, in the sandy soil, in the activated sludge soil, and in the farm soil at 28, 37, and 608C, respectively. Seven PHB degrading fungi, five SG degrading fungi, and six MB degrading fungi were isolated by analyzing the microbiological characteristics of the fungi. Biodegradation of all three polymers was most active in the activated sludge soil. Both SG and MB showed higher degradability at 288C than at 378C. Biodegradability of PHB was highest at 378C, while degradation of MB occurred reasonably well at 608C. In the modified Sturm test Penicillium simplicissimum LAR 13 and Paecilomyces farinosus LAR 10 degraded PHB relatively well, while the degradation rate by Aspergillus fumigatus LAR 9 was lower than expected. P. simplicissimum LAR 13 showed the highest degradation rate for SG and A. fumigatus LAR 9 was most eAective in degrading MB. Biodegradability of isolated fungi was aAected by the incubation temperature. In both the soil burial test and the modified Sturm test the order of the biodegradation rate was PHB > SG > MB. 7 2000 Elsevier Science Ltd. All rights reserved.

Crystallization behavior of biodegradable amphiphilic poly(ethylene glycol)‐poly(L‐lactide) block copolymers

Poly(ethylene glycol)-poly(L-lactide) diblock and triblock copolymers were prepared by ring-opening polymerization of L-lactide with poly(ethylene glycol) methyl ether or with poly(ethylene glycol) in the presence of stannous octoate. Molecular weight, thermal properties, and crystalline structure of block copolymers were analyzed by 1H-NMR, FTIR, GPC, DSC, and wide-angle X-ray diffraction (WAXD). The composition of the block copolymer was found to be comparable to those of the reactants. Each block of the PEG–PLLA copolymer was phase separated at room temperature, as determined by DSC and WAXD. For the asymmetric block copolymers, the crystallization of one block influenced much the crystalline structure of the other block that was chemically connected to it. Time-resolved WAXD analyses also showed the crystallization of the PLLA block became retarded due to the presence of the PEG block. According to the biodegradability test using the activated sludge, PEG–PLLA block copolymer degraded much faster than PLLA homopolymers of the same molecular weight.

Living radical copolymerization of styrene/maleic anhydride

Styrene/maleic anhydride (MA) copolymerization was carried out using benzoyl peroxide (BPO) and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). Styrene/MA copolymerization proceeded faster and yielded higher molecular weight products compared to styrene homopolymerization. When styrene/MA copolymerization was approximated to follow the first-order kinetics, the apparent activation energy appeared to be lower than that corresponding to styrene homopolymerization. Molecular weight of products from isothermal copolymerization of styrene/MA increased linearly with the conversion. However products from the copolymerization at different temperatures had molecular weight deviating from the linear relationship indicating that the copolymerization did not follow the perfect living polymerization characteristics. During the copolymerization, MA was preferentially consumed by styrene/MA random copolymerization and then polymerization of practically pure styrene continued to produce copolymers with styrene-co-MA block and styrene-rich block.

Biochemical oxygen demand sensor using Serratia marcescens LSY 4

A microbial biochemical oxygen demand (BOD) sensor consisting of Serratia marcescens LSY 4 and an oxygen electrode was prepared for estimation of the biochemical oxygen demand. The response of the BOD sensor was insensitive to pH in the range of pH 6.0-8.0, and the baseline drift of the signal was nearly absent even in unbuffered aqueous solution. Because heavy metal ions were precipitated from the phosphate buffer solution, unbuffered solution was used to investigate the effect of the concentration of heavy metal ions on the sensor response. Contrary to previous studies, not only Cu2+ and Ag+ but also Cd2+ and Zn2+ significantly decreased the response of the BOD sensor in unbuffered solution. Graft polymerization of sodium styrene sulfonate on the surface of the porous teflon membrane was carried out to absorb the heavy metal ions permeating through the membrane. Tolerance against Zn2+ was induced for S. marcescens LSY 4 to make the cells less sensitive to the presence of heavy metal ions. The membrane modification and the Zn2+ tolerance induction showed some positive effects in such a way that they reduced the inhibitory effects of Zn2+ and Cd2+ on the sensitivity of the BOD sensor. However, they had no effect on the protection of the cells against the interference of Cu2+ and Ag+ on the performance of the sensor.

Antifungal effect of carbendazim supported on poly(ethylene‐co‐vinyl alcohol) and epoxy resin

Ethylene-vinyl alcohol copolymers (EVOH) were prepared by the conventional saponification of poly(ethylene-co-vinyl acetate) using a solution of potassium hydroxide in ethanol. An organic fungicide, consisting of a 2-benzimidazole carbamoyl (CBZ) group supported on EVOH (EVOH-CBZ), was prepared by the transesterification reaction of methyl 2-benzimidazole cabamate (carbendazim) with EVOH. The antifungal activity of the synthesized polymers was examined by the halo zone test against Aspergillus fumigatus and Penicillium pinophilum. The synthesized EVOH-CBZ complex showed a strong antifungal activity. The bound CBZ units were susceptible to hydrolysis. CBZ bonded to an epoxy resin precursor, diglycidyl ether of bisphenol A (DGEBA-CBZ), retained its antifungal activity, which was somewhat weaker in comparison with that of EVOH-CBZ. When the DGEBA-CBZ complex was crosslinked by isophoronediamine, the antifungal activity disappeared almost completely, indicating that it is necessary for the CBZ units to release from their polymer supports to have the antifungal effects.

Biodegradability of ethyl and n-octyl branched poly(ethylene adipate) and poly(butylene succinate)

Abstract Ethylene glycol/adipic acid and 1,4-butanediol/succinic acid were copolymerized in the presence of 1,2-butanediol and 1,2-decanediol to produce ethyl and n-octyl branched poly(ethylene adipate) (PEA) and poly(butylene succinate) (PBS), respectively. The chain branching reduced the crystallinity of PEA more significantly than the crystallinity of PBS. Surface tension of PEA was higher than that of PBS, though the two polyesters have identical number of methylene groups and ester groups in the repeating unit. However the modified Sturm test showed that the two polymers were assimilated to CO2 at a similar rate. As the degree of chain branching increased, the biodegradation rate of PEA increased to a greater extent than that of PBS due to the faster reduction in the crystallinity of PEA compared to the crystallinity of PBS.

Properties and biodegradation of poly(ethylene adipate) and poly(butylene succinate) containing styrene glycol units

Mechanical and thermal properties together with biodegradability of poly(butylene succinate) (PBS) and poly(ethylene adipate) (PEA) were investigated when phenyl branches were introduced into the aliphatic polyesters by copolymerizing styrene glycol with the diacids and the diols. Increasing content of styrene glycol units decreased Tm, crystallinity and molecular weight of the aliphatic copolyesters, which concurrently decreased the tensile properties. Tg was raised from −47°C for PEA to 30°C for poly(styrene succinate). The copolyesters containing higher content of sytrene glycol units were mineralized faster into CO2 in the modified Sturm test. However, the rate of bond cleavage by an abiotic hydrolysis was nearly independent of the presence of styrene glycol units.

Blending of poly(L-lactic acid) with poly(cis-1,4-isoprene)

Abstract Poly( L -lactic acid) (PLLA), a brittle biodegradable thermoplastic polymer, was blended with rubbery poly(cis-1,4-isoprene) (PIP). The PLLA/PIP blend, however, was incompatible as indicated by two T g ’s, each stemming from PLLA and PIP domains, respectively. Since PLLA was known to be compatible with poly(vinyl acetate) (PVAc), PIP was grafted with vinyl acetate monomer to form PIP-g-PVAc, which was then blended with PLLA. The blend of PLLA and PIP-g-PVAc had two T g ’s. The lower T g , which was due to PIP phase, did not vary with the blend composition, while the higher T g , which was due to PLLA rich phase, decreased with an increase in the graft copolymer content. The PVAc moiety of the graft copolymer seems to have been mixed in with PLLA. The tensile properties of the PLLA/PIP-g-PVAc blend were much superior to those of the PLLA/PIP blend.