Irene Kit Ping Tan

A kinetic model for growth and biosynthesis of medium-chain-length poly-(3-hydroxyalkanoates) in Pseudomonas putida

A kinetic model is presented giving a mathematical description of batch culture of Pseudomonas putida PGA1 grown using saponified palm kernel oil as carbon source and ammonium as the limiting nutrient. The growth of the micro-organism is well-described using Tessier-type model which takes into account the inhibitory effect of ammonium at high concentrations. The ammonium consumption rate by the cells is related in proportion to the rate of growth. The intracellular production of medium-chain-length poly-(3-hydroxyalkanoates) (PHAMCL) by P. putida PGA1 cells is reasonably modeled by the modified Luedeking-Piret kinetics, which incorporate a function of product synthesis inhibition (or reduction) by ammonium above a threshold level.

Isolation of polyhydroxyalkanoate-producing bacteria from an integrated-farming pond and palm-oil mill effluent ponds

Bacterial isolates from two environments, an integrated-farming pond in the university and palm-oil mill effluent (POME) ponds at a local palm-oil-processing factory, were screened for polyhydroxyalkanoates (PHAs). Initially Sudan Black B staining was performed to detect lipid cellular inclusions. Lipid-positive isolates were then grown in a nitrogen-limiting medium containing 2% (w/v) glucose to promote accumulation of PHA before the subsequent Nile Blue A staining. The PHA extracted from positive isolates was confirmed by nuclear magnetic resonance (NMR) spectroscopy. The proportion of PHA-positive bacterial isolates was higher in the POME ponds compared to the integrated-farming pond.

Characterization of Oligomeric Hydroxyalkanoic Acids from Thermal Decomposition of Palm Kernel Oil–Based Biopolyester

Oligomeric hydroxyalkanoic acids can be prepared by thermal decomposition of the original polyesters at moderate high temperature. In this study, low molecular weight hydroxyl acids were produced by heat treating of saponified palm kernel oil-derived medium-chain-length polyhydroxyalkanoates (mcl-PHA) in the temperature range of 160°–190°C. Thermal stability, glass transition temperature, and degree of crystallinity of mcl-PHA before and after thermal treatments were characterized by Thermogravimetric Analysis and Differential Scanning Calorimetry measurements. Changes in molecular weight and the acidity of decomposition products were investigated by Gel Permeation Chromatography and end group analyses, respectively. An increase in the acidity of oligomeric hydroxyalkanoic acids was observed when the molecular weight of the oligomers decreased. This was primarily due to the formation of thermodynamically stable hydroxyl-carboxylate ions and the protons in aqueous solutions when heat is supplied to the system.

Viscoelastic, Spectroscopic, and Microscopic Characterization of Novel Bio-Based Plasticized Poly(vinyl chloride) Compound

Plasticized poly(vinyl chloride) (PVC) is one of the most widely consumed commodity plastics. Nevertheless, the commonly used plasticizers, particularly phthalates, are found to be detrimental to the environment and human health. This study aimed to investigate the ability of an alternative greener material, medium-chain-length polyhydroxyalkanoates (mcl-PHA), a kind of biopolyester and its thermally degraded oligoesters, to act as a compatible bioplasticizer for PVC. In this study, mcl-PHA were synthesized by Pseudomonas putida PGA1 in shake flask fermentation using saponified palm kernel oil (SPKO) and subsequently moderately thermodegraded to low molecular weight oligoesters (degPHA). SEM, ATR-FTIR, 1H-NMR, and DMA were conducted to study the film morphology, microstructure, miscibility, and viscoelastic properties of the PVC-PHA and PVC/degPHA binary blends. Increased height and sharpness of tan peak for all binary blends reveal an increase in chain mobility in the PVC matrix and high miscibility within the system. The PVC-PHA miscibility is possibly due to the presence of specific interactions between chlorines of PVC with the C=O group of PHA as evidenced by spectroscopic analyses. Dynamic viscoelastic measurements also showed that mcl-PHA and their oligoesters could reduce the of PVC, imparting elasticity to the PVC compounds and decreasing the stiffness of PVC.