Chia Hock Leong Lawrence
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dvochll@nus.edu.sg
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Publication Rotational isomerism in 2,3-dinitro-2,3-dimethylbutane(1984) Tan, B.-G.; Chia, L.H.L.; Huang, H.-H.; Kuok, M.-H.; Tang, S.-H.; CHEMISTRYI.r. and Raman spectra of 2,3-dinitro-2,3-dimethylbutane (in the solid and solution states) are reported and assignments of frequencies made. Comparison of the Raman and i.r. spectra of the solid shows that the compound exists in the graucae-conformation in the solid state. Dipole moments in different solvents (benzene, carbon tetrachloride, dioxane, and cyclohexane) at different temperatures and molar Kerr constants (in carbon tetrachloride and benzene) are also reported. Analysis of the physical data shows that, at 25°C, 2,3-dinitro-2,3-dimethylbutane exists as a rotameric mixture of 42% gauche and 58% trans in carbon tetrachloride solution, and 79% gauche and 21% trans in benzene solution. Solvent effects are also discussed.Publication Preliminary investigations on a new method of retaining the colour of shucked cockles (Anadara Granosa), and the extension of shelflife by gamma irradiation and vacuum packing(1987) Ng, C.S.; Low, L.K.; Chia, L.H.L.; CHEMISTRYLive cockles were incubated in atmospheres containing different concentrations of carbon monoxide. Since CO combines more readily with myoglobin and haemoglobin than oxygen, the formation of in vivo deoxygenated haemoglobins and post mortem formation of methaemoglobin were retarded by the more stable carboxyhaemoglobin (HbCO). The bright red colour of the stable HbCO is retained during storage, giving the desired colour to the cockles. The colour of normal, chilled cockle meat deteriorated after 3 days ice storage while those treated with 50 and 100% CO retained the bright deep orange colour up to 10 days storage. Irradiation caused faster colour deterioration in both CO and non-CO treated samples. Vacuum packing influenced the colour of the cockles with irradiation and with CO treatments. In non-CO treated, irradiated samples, the effect of vacuum packing was not obvious. In CO treated, irradiated samples, vacuum packing retarded the deterioration of colour. Odour developments were influenced by irradiation, vacuum packing and storage temperature, and were not influenced by CO treatments. Irradiation suppressed the development of odour for the first 11 days storage (0°C) while vacuum packing depressed the odour by lowering its intensity instead. Odour development was slowed down by lowering the storage temperature. The odour of shucked cockles was rejected within one day at room temperature (26-28°C) while at 0°C the odour of the shucked cockles was still acceptable after 10 days. Suitable chemical indices for quality are K value and TVBN. Treatment with CO did not influence the K value development. Vacuum packing produced the highest K values after 19 days storage (0°C), while irradiated samples had higher K values than non-irradiated samples. The TVBN increased with storage and is an indicator of the odour development. The use of CO treatment extended the shelflife of the cockles based on appearance. A combination of CO treatment, vacuum packing, ice storage and irradiation extended the shelflife to beyond 18 days, based on odour, colour, and overall appearance. © 1987.Publication Resistance of radiation-induced tropical wood-polymer composites to fungal degradation(1987) Chia, L.H.L.; Lim, V.S.L.; Yap, M.G.S.; CHEMICAL ENGINEERING; CHEMISTRYThe resistance of six tropical hardwoods to fungal degradation by two wild-type strains of Phanerochaete chrysosporium Burdsall was investigated using vermiculite burial and wood-block weight loss techniques. Radiation-induced wood-polymer composites (WPC), based on two hardwoods Ramin and Rubber-wood with methyl methacrylate, were prepared, and samples were also exposed to the wood-rotting fungus. A significant improvement in resistance to fungal decay was observed in the WPC. Scanning-electron micrographs of the two woods and their composites after fungal degradation are presented and discussed. © 1987.Publication Thermal characterization of rubberwood-polymer composites(1989) Chan, K.Y.; Yap, M.G.S.; Chia, L.H.L.; Neoh, K.G.; CHEMICAL ENGINEERING; CHEMISTRYThe thermal properties of five types of radiation-induced wood-polymer composites based on a tropical hardwood, rubberwood (Hevea braziliensis), was studied by oxygen index measurement, differential thermal analysis (DTA) and thermogravimetry (TG). The DTA and TG curves of composites were different from those of rubberwood, which can be attributed to the presence of the incorporated polymers. Of the five composites, the one impregnated with bis(2-chloroethyl)vinyl phosphonate reduced the initial temperature of decomposition, increased the peak temperatures of exothermic reactions, and increased the char yield. Comparison with physical blends of rubberwood and the corresponding polymer provided some evidence of chemical interaction of wood and polymer in some of the composites. © 1989.Publication Practical microwave curing studies for undergraduates(1999-10) Ng, L.-T.; Chia, L.H.L.; ALUMNI AFFAIRS & DEVELOPMENT OFFICEMicrowave curing has recently generated interest as an alternative to the conventional thermal curing of polymers. Advantages of the microwave process over the thermal method include faster curing times, improved efficiency of curing, and enhanced properties of the polymers. This paper describes an undergraduate polymer chemistry experiment utilizing a domestic microwave oven for the curing of methyl methacrylate. Thermal curing was also carried out as a comparative study. The percentage conversions at fixed time intervals using both processes were determined using FTIR spectroscopy. Results show that the percentage conversions using the thermal method increased slowly over the 18min reaction time. However, there was a significant increase in the rate of polymerization at the end the same reaction period using the microwave method, equivalent to 3.5 times that of the thermal method. This experiment successfully demonstrates that microwave method is not only a safe but also a reliable and faster alternative to the thermal method of curing some polymers. © 1999 Society of Chemical Industry.Publication MODEL FOR THE COMPRESSION FAILURE OF AN IRRADIATED TROPICAL WOOD-POLYMER COMPOSITE.(1987) Boey, F.Y.C.; Chia, L.H.L.; Teoh, S.H.; CHEMISTRY; MECHANICAL & PRODUCTION ENGINEERINGUsing a gamma irradiation method, some tropical wood-polymer composites were produced which exhibited a significant improvement in uniaxial compressive strength. Although compression failure models have been established for normal uniaxial fiber reinforced composites, for both direct compression failure and by microbuckling compression failure, the unique structure of wood-polymer composite does not allow these same models to adequately describe its compression failure. Experimental results indicated that the failure criterion in a uniaxial compression test for the wood-polymer composite was based on the buckling failure of the wood fiber and impregnated polymer along a shear band. Using this buckling failure criterion, a model was proposed that took into account the stiffening effect of the impregnated polymer on the wood cell wall.Publication FTIR characterization of tropical wood-polymer composites(1991-12-05) Yap, M.G.S.; Que, Y.T.; Chia, L.H.L.; CHEMICAL ENGINEERING; CHEMISTRYWood-polymer composites (WPC) of Geronggang (Cratoxylon arborescens), a light tropical hardwood, impregnated with methyl methacrylate (MMA), methyl methacrylate-co-acrylonitrile (1:1; MAN), and styrene-co-acrylonitrile (3:2; STAN), were prepared by in situ polymerization using gamma radiation or the catalyst-heat treatment. The FTIR spectra of the three types of WPC, with polymer loadings ranging from 10 to 70%, were compared with that of the wood itself and the respective polymers. Characteristic peaks du to C=O vibration of MMA, ≡N stretching of acrylonitrile, and ring stretching and bending of styrene monomers, were prominent in the samples that had higher polymer loadings. For the copolymeric systems, quantitation of the FTIR spectra of these characteristic peaks enabled calculations of incorporated acrylonitrile and styrene monomers in the composites to be made. The FTIR spectra of the residues remaining, after exhaustive extraction to remove homopolymer, showed that graft copolymerization of wood components with acrylonitrile and styrene monomers was possible, but not with MMA. Composites prepared by the two methods, gamma radiation and the catalyst-heat treatment, were shown to be chemically very similar.Publication The microwave radiation effect on the polymerization of styrene(1996-08) Chia, H.L.; Jacob, J.; Boey, F.Y.C.; CHEMISTRYStyrene was cured by microwave radiation at two different powers: 300 and 500 W. The temperature profile of the sample during the microwave curing process was determined to select a suitable temperature for comparison with the conventional method of cure. The results indicate a similar comparable temperature of about 80°C irrespective of the microwave power used. The percentage conversion of the cure was followed by Fourier transform infrared (FTIR) spectroscopy. The thermal polymerization at 79(±1)°C displayed a gradual increase in the rate of reaction at the gel effect from about 30 to 50% conversion of the reaction. The microwave cure at 300 and 500 W displayed a large and sharp gel effect from about 20 to 69 and 64% conversion of the reaction, respectively. The limiting conversion decreased with increase in microwave power which was also observed in the polymerization of methyl methacrylate (MMA). Based on similarity in temperature and reaction conditions, the 500 W cure was found to show a reaction rate enhancement of 190% and the 300 W cure 120%. A comparison of microwave induced reactions with thermal methods, therefore, must also specify the microwave power used. © 1996 John Wiley & Sons, Inc.Publication Thermal properties of tropical wood-polymer composites(1991-12-05) Yap, M.G.S.; Que, Y.T.; Chia, L.H.L.; Chan, H.S.O.; CHEMICAL ENGINEERING; CHEMISTRYWood-polymer composites (WPC) of Geronggang (GE; Cratoxylon arborescens), a light tropical hardwood, impregnated with methyl methacrylate (MMA), styrene-co-acrylonitrile (3:2; STAN), methyl methacrylate-co-bis(2-chloroethyl)vinyl phosphonate (3:1; MVP) and methyl methacrylate-co-bis(chloropropyl)-2-propene phosphonate (3:1; MPP), were prepared by in situ polymerization using γ-radiation or catalyst-heat treatment. Thermal characterization of these WPC by limiting oxygen index measurements (LOI), thermogravimetry (TG), and differential scanning calorimetry (DSC) showed that the impregnants greatly modified the wood properties. The LOI values of the GE-MVP and GE-MPP composites were much higher than that for GE and the other composites, indicating the effectiveness of the phosphonates as flame retardants. Concomitantly, the flaming characteristics also compared favorably against that for GE and the other composites. The decomposition temperature and maximum rate of weight loss determined by TG for GE-MVP and GE-MPP were substantially reduced, whereas the char yields were greatly higher. These observations again indicate that phosphonates imparted flame-retarding properties to their composites. The thermal properties of GE-MMA and GE-STAN composites were not vastly different from that of untreated GE. Flame retardancy in the phosphonate-containing composites was effected through both the condensed- and gaseous-phase mechanisms due to the presence of phosphorus and chlorine, respectively. Indication of grating of polymer to wood was found for GE-STAN, GE-MVP, and GE-MPP composites, but not for GE-MMA. Composites prepared by γ-radiation or by the catalyst-heat treatment had similar thermal characteristics.Publication REDUCING THE MOISTURE EFFECT ON THE CREEP DEFORMATION OF WOOD BY AN IRRADIATION-INDUCED POLYMER IMPREGNATION METHOD.(1988) Chia, L.H.L.; Boey, F.Y.C.; Teoh, S.H.; CHEMISTRY; MECHANICAL & PRODUCTION ENGINEERINGThis paper reports an attempt to reduce the sensitivity of creep deformation to moisture adsorption by impregnating a tropical wood with methyl-methacrylate and subsequent polymerization by gamma -irradiation. Beam specimens both of untreated wood and polymer impregnated wood were subjected to a three-point bend creep test under a constant load of 300 N at 23 plus or minus 1 degree C, at three different humidity levels of 50 plus or minus 5, 65 plus or minus 5 and 85 plus or minus 5%. A Norton-Bailey (power law) mathematical model successfully described the creep behavior, with the creep components determined by a nonlinear regression analysis. A significant reduction in the sensitivity of creep deformation to the humidity level was attained for the polymer impregnated wood. This could be explained by the ability of the impregnated polymer to form a strongly adhesive interface with the wood cell material, thereby acting as a physical barrier to reduce the movement of water to and from the wood cell material.