Syed H. Imam

Extruded Cornstarch-Glycerol-Polyvinyl Alcohol Blends: Mechanical Properties, Morphology, and Biodegradability

Elongation properties of extruded cornstarch were improved by blending with glycerol. Further blending of starch-glycerol with polyvinyl alcohol (PVOH) resulted in significant improvements in both tensile strength (TS) and elongation at break. Samples of starch-glycerol without PVOH equilibrated at 50% relative humidity had a TS of 1.8 MPa and elongation of 113%, whereas those containing PVOH had a TS and elongation of 4 MPa and 150%, respectively. Dynamic mechanical analysis (DMA) of starch-glycerol-PVOH blends showed that decreases in glass transition temperatures (Tg values) were proportional to glycerol content. Scanning electron microscopy (SEM) of fractured surfaces revealed numerous cracks in starch-glycerol (80:20) samples. Cracks were absent in starch-glycerol (70:30) samples. In both blends, many starch granules were exposed at the surface. No exposed starch granules were visible in blends with added PVOH. Starch-glycerol samples incubated in compost lost up to 70% of their dry weight within 22 days. Addition of PVOH lowered both the rate and extent of biodegradation.

Environmentally friendly wood adhesive from a renewable plant polymer: characteristics and optimization

A wood adhesive was prepared from a natural renewable resource. The characteristics and optimization of starch and polyvinyl alcohol (PVOH)-based crosslinked adhesive suitable for wood-to-wood bonding in interior applications are described. The crosslinker, hexamethoxymethylmelamine (Cymel 323) produced effective crosslinking through a transetherification reaction between methoxy groups in Cymel 323 and hydroxyl groups in starch, PVOH and wood, where hydroxyl groups replaced methoxy groups forming ether bonds with the crosslinker. Optimal viscosity of the adhesive was obtained at 27% solid content. Addition of latex in the formulation increased moisture resistance. The optimum cure temperature and cure time were 175°C and 15 min. Wood samples conditioned at 93% RH for two months exhibited >95% failure in wood but little in adhesive joints. Scanning electron microscopy revealed no visible growth of fungi or other microorganisms on the adhesive after two months exposure of samples at 97% RH followed by 1 year at 50% RH.

Factors Affecting Microbial Degradation of Polycyclic Aromatic Hydrocarbon Phenanthrene in the Caribbean Coastal Water

Abstract Studies were conducted to assess factors that may influence the rate and extent of biodegradation of polyaromatic hydrocarbons (PAHs) in waters of Guayanilla Bay (latitude, 18°N; longitude, 66.45°W) Puerto Rico. Phenanthrene was used as a model PAHs compound. Both the rate and extent of phenanthrene degradation by natural microbial flora present in seawater samples from Guayanilla Bay were quite slow. Addition of KNO 3 as a source of inorganic nitrogen (N) resulted in a 10-fold increase in the rate of phenanthrene degradation within a 125 h period, whereas, addition of K 2 HPO 4 as a source of inorganic nutrient phosphorus (P) had no effect. Phenanthrene degradation was strongly inhibited when seawater pH was adjusted to 10.0. Phenanthrene in seawater samples degraded rapidly when first pretreated with hydrogen peroxide (H 2 O 2 ) and then inoculated with a known indigenous phenanthrene degrading bacterium, Alteromonas sp. Pretreatment of phenanthrene with Triton- x -100 had little or no effect on its degradation by the same bacteria, whereas, degradation in samples preheated at 60°C was somewhat inhibited.

Biodegradation of starch-poly(β-hydroxybutyrate-co-valerate) composites in municipal activated sludge

Injection-molded composites were prepared by blending PHBV5 with native cornstarch (30% and 50%) and with cornstarch precoated with PEO as a binding agent. These composites were evaluated for their biodegradability in municipal activated sludge by measuring changes in their physical and chemical properties over a period of 35 days. All composites lost weight, ranging from 45 to 78% within 35 days. Interestingly, the extent and rate of weight loss were quite similar in PHBV composites with no starch, with 30% starch, and with 50% starch. Weight loss was slowest in PHBV blends prepared with PEO-coated starch. For all samples, the weight loss was accompanied by a rapid deterioration in tensile strength and percentage elongation. The deterioration of these mechanical properties exhibited a relative rate of PHBV>starch-PHBV>PEO-coated starch-PHBV. Changes in starch/PHBV composition after biodegradation were quantified by FTIR spectroscopy. Increasing the starch content resulted in more extensive starch degradation, while the PHBV content in the blends became less susceptible to hydrolytic enzymes.

A study of cornstarch granule digestion by an unusually high molecular weightα-amylase secreted byLactobacillus amylovorus

The cells ofLactobacillus amylovorus (NRRL B-4540), grown in a medium containing 2% cornstarch as the sole carbon source, secreted an amylase activity that rapidly solubilized cornstarch. Fourier transform infrared (FTIR) spectroscopic analyses showed that 80–90% of starch was consumed by bacteria in a 10-day-old culture medium. The remnant of starch granules digested in the culture medium inoculated with the cells ofL. amylovorus have also lost their characteristic iodine-binding capacity as visualized by starch dye-binding microplate assay and light microscopy. Scanning electron miscroscopy (SEM) of granules from a 48-h culture medium showed hollow and fragmented granules with a pitting phenomenon characteristically produced byα-amylase activity. Analysis of an enzyme preparation from a culture medium ofL. amylovorus revealed that the putative enzyme appears to be a single protein band of unusually high Mr (150,000) on SDS gels stained for amylase activity. Analysis of starch digestion products by thin layer chromatography (TLC) showed enzyme activity typical ofα-amylase.

Biodegradation of Injection Molded Starch-Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) Blends in a Natural Compost Environment

Injection molded specimens were prepared by blending poly (hydroxybutyrate-co-valerate) (PHBV) with cornstarch. Blended formulations incorporated 30% or 50% starch in the presence or absence of poly-(ethylene oxide) (PEO), which enhances the adherence of starch granules to PHBV. These formulations were evaluated for their biodegradability in natural compost by measuring changes in physical and chemical properties over a period of 125 days. The degradation of plastic material, as evidenced by weight loss and deterioration in tensile properties, correlated with the amount of starch present in the blends (neat PHBV < 30% starch < 50% starch). Incorporation of PEO into starch-PHBV blends had little or no effect on the rate of weight loss. Starch in blends degraded faster than PHBV and it accelerated PHBV degradation. Also, PHBV did not retard starch degradation. After 125 days of exposure to compost, neat PHBV lost 7% of its weight (0.056% weight loss/day), while the PHBV component of a 50% starch blend lost 41% of its weight (0.328% weight loss/day). PHB and PHV moieties within the copolymer degraded at similar rates, regardless of the presence of starch, as determined by 1H-NMR spectroscopy. GPC analyses revealed that, while the number average molecular weight (Mn) of PHBV in all exposed samples decreased, there was no significant difference in this decrease between neat PHBV as opposed to PHBV blended with starch. SEM showed homogeneously distributed starch granules embedded in a PHBV matrix, typical of a filler material. Starch granules were rapidly depleted during exposure to compost, increasing the surface area of the PHBV matrix.

Partial purification and comparative characterization of α-amylase secreted byLactobacillus amylovorus

An α-amylase (E.C. 3.2.1.1.) secreted byLactobacillus amylovorus was partially purified and characterized. This high-molecular-weight enzyme [Imam SH, Burgess-Cassler A, Côté GL, Gordon SH, Baker FL (1991) Curr Microbiol 22:365–370] was quantified with a clinical α-amylase assay adapted to a microplate format. It was isolated from concentrated cell-free culture medium by ammonium sulfate precipitation, ion exchange, and hydrophobic interaction chromatographies. The enzyme was not particularly thermostable, but like three other microbial α-amylases tested for comparison, was renaturable following treatment with SDS and heat. The pH optimum and pI were 5.5±0.5 and 5.0, respectively; its temperature optimum was 60–65°C, and the molecular weight on SDS gels was 140±10 kDa.

Accelerated Biodegradation of High and Low Concentrations of p-Nitrophenol (PNP) by Bacterial Inoculation in Industrial Wastewater: The Role of Inoculum Size on Acclimation Period

Abstract. The effect of inoculum size on the acclimation period and rate and extent of p-nitrophenol (PNP) degradation at high (1–10 mg/L) and low (26 μg/L) concentrations for two bacteria was determined in defined media as well as industrial wastewater. Increased inoculum size did not affect the acclimation period of either bacterium at high (1–10 mg/L) PNP concentrations. At low PNP concentrations (26 μg/L), the two bacteria behaved differently. The acclimation period was shortened and both the rate and extent of mineralization of PNP were enhanced by increasing the Corynebacterium sp. inoculum size from 3 × 105 to 3 × 106 cells/ml. Addition of phosphate or elimination of predators also reduced the acclimation period. Conversely, increasing the inoculum size from 3 × 105 to 5 × 106 cells/ml of Pseudomonas putida lengthened the acclimation period and reduced both the rate and extent of mineralization. It is suggested that, in a given environment, the success of an introduced species to enhance the degradation of a chemical depends upon (i) concentration of the chemical, (ii) selection of an appropriate microorganism, and (iii) utilization of a suitable inoculum size.

A semiempirical model for predicting biodegradation profiles of individual polymers in starch-poly- (?-hydroxybutyrate-co-?-hydroxyvalerate) bioplastic

Plastic prepared from formulations of cornstarch and poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PHBV) biodegraded in tropical coastal waters. Biodegradation was monitored for 1 year. Starch - PHBV bioplastic appeared to lose weight in two overlapping phases until both biopolymers were entirely consumed. To examine the underlying degradation of starch and PHBV from biphasic weight-loss profiles, a semiempirical mathematical model was developed from which degradation profiles and lifetimes of the individual biopolymers could be predicted. The model predicted that starch and PHBV in the bioplastic had half-lives of 19 days and 158 days, respectively. Computed profiles also predicted that the starch in the composite would be completely degraded in 174 days, while residual PHBV would persist in the marine environment for 1107 days. The model further revealed that, for a 30% starch : 70% PHBV composite, PHBV degradation was delayed 46 days until more than 65% of the starch was consumed. This suggested that PHBV degradation was metabolically repressed by glucose derived from starch. Glucose repression of microbial PHBV degradation was substantiated in 91 of 100 environmental isolates. The validity of the elaborated model was proven when its revelations and predictions were later confirmed by chemical analysis of residual bioplastic samples.

The use of CP/MAS 13C-NMR for evaluating starch degradation in injection molded starch-plastic composites

Cross-polarization/magic angle spinning (CP/MAS) 13C solid-state-NMR was utilized to evaluate the extent of hydrolysis and structure of starch in enzymatically digested injection molded starch-polyethylene-co-acrylic acid (EAA)-polyethylene (PE) plastic composites. It is a simple, quick and semi-quantitative method. Results are in agreement with reducing sugar assays routinely used for measuring starch degradation.