Seng Neon Gan

Saponified palm kernel oil and its major free fatty acids as carbon substrates for the production of polyhydroxyalkanoates in Pseudomonas putida PGA1

Abstract The synthesis of polyhydroxyalkanoates (PHA) by Pseudomonas putida PGA1, using saponified palm kernel oil (SPKO), was investigated. The PHA produced from SPKO was compared with those produced by the major free fatty acids found in the palm kernel oil. Owing to the absence of lipase activity in P.␣putida, palm kernel oil did not support cell growth. However, SPKO could support cell growth and produced relatively high yield of both dry cells and PHA. The polyester produced was similar in properties to those derived from lauric (C12:0) and myristic (C14:0) acids, while oleic acid (C18:1) gave rise to PHA that was sticky and of broader molecular mass distribution. Nuclear magnetic resonance and gas chromatography showed that these PHA were copolymers consisting mainly of n-alkanoate monomers ranging from C6 to C14, with C8 as the predominant component. PHA derived from SPKO and oleic acid also contained a small amount of unsaturated monomers.

Partial conversion of epoxide groups to diols in epoxidized natural rubber

Abstract Epoxidized natural rubber (ENR) is fairly stable in its latex state. Only a small amount of the epoxide groups were converted to diols when the latex was boiled under mildly acidic or alkaline pH. Although the small amount of diols could not be determined accurately by 1 H nuclear magnetic resonance (n.m.r.), their presence could be demonstrated by the degradation reaction using lead tetraacetate. The formation of -OH and carbonyl groups after the degradation could be clearly seen in the infra-red spectra. Higher level of diols could be introduced by reacting ENR-50 dissolved in toluene with a mixture containing water and acetic acid in tetrahydrofuran at 60°C. The amount of conversion of epoxide to diol increases with reaction time, and up to 23 mol% of diol in the rubber chain can be achieved after 24 h of reaction. The extent of conversion can be determined from the 1 H n.m.r. spectra of the samples. The ENR containing diols in the main chain could serve as a good intermediate for further chemical modifications. For example, cleavage of the diol groups with specific reagents could offer a convenient route to the production of liquid ENR.

Determination of avrami exponent by differential scanning calorimetry for non-isothermal crystallization of polymers

Abstract A novel approach was developed to study the non-isothermal crystallization kinetics of polymers based on the Ozawa equation. The method determines the Avrami exponent, n , using exclusively the data confined to the primary crystallization regime. It was applied to a selection of eleven semicrystalline polymers including some biodegradable polyesters. The differential scanning calorimetry exotherms were obtained from the cooling rates covering 2 to 40 K min −1 . As noted, poly(-caprolactone) and nylon 6,10 resulted in the lowest and highest n , being equal to 1.5 and 5.1, respectively. The present findings on n were compared with those reported in the literature. Their morphological implications were also discussed.

ATR-FTIR studies on ion interaction of lithium perchlorate in polyacrylate/poly(ethylene oxide) blends

The interaction behaviours between components of polyacrylate (PAc)/poly(ethylene oxide) (PEO) and lithium perchlorate (LiClO(4)) were investigated in detail by Attenuated Total Reflectance (ATR)-Fourier Transformed Infrared (FTIR) spectroscopy. Solution cast films of the PAc/PEO and PAc/PEO/LiClO(4) were examined. No obvious shifting of the characteristic ether and ester group stretching modes of PEO and PAc was observed, indicating incompatibility of the binary PAc/PEO blend. The spectroscopic studies on the PAc/PEO/LiClO(4) blends reveal that Li(+) ions coordinate individually to the polymer components at the ether oxygen of PEO and the C-O of the ester group of PAc. Frequency changes observed on the nu(C-O-C) and omega(CH(2)) of PEO confirm the coordination between PEO and Li(+) ions resulting in crystallinity suppression of PEO. The absence of experimental evidence on the formation of PEO-Li(+)-PAc complexes suggests that LiClO(4) does not enhance the compatibility of PAc/PEO blend.

Theoretical and experimental approach on dielectric properties of ZnO nanoparticles and polyurethane/ZnO nanocomposites

ZnO nanoparticles (ZnO-NPs) were synthesized by a new, simple sol-gel method in gelatin media (particle size of ZnO ≈ 30 to 60 nm). Polyurethane/ZnO nanocomposites thin films (PU/ZnO-NPs) were prepared by mixing the ZnO-NPs into PU prepolymer. The nanocomposites were structurally characterized using Fourier transmission infrared (FTIR) spectroscopy. The interaction between ZnO-NPs and PU matrix is studied by analyzing the differences in C=O region and N-H region of FTIR spectra. The morphology of ZnO and PU/ZnO nanocomposites were assessed using transmission electron micrograph, TEM, and field emission scanning electron microscope, FESEM, respectively. The dielectric properties of ZnO-NPs were attributed to the interfacial and orientation polarization. Measurement is reported for the real and imaginary parts of the ac conductivity of ZnO-NPs in the frequency range of 10 to 106 Hz in the temperature range 298–478 K. The experimental results are interpreted in terms of the classical correlated-barrier hoppi...

Polymethacrylate coated electrospun PHB fibers: An exquisite outlook for fabrication of paper-based biosensors

Electrospun polyhydroxybutyrate (PHB) fibers were dip-coated by polymethyl methacrylate-co-methacrylic acid, poly(MMA-co-MAA), which was synthesized in different molar ratios of the monomers via free-radical polymerization. Fabricated platfrom was employed for immobilization of the dengue antibody and subsequent detection of dengue enveloped virus in enzyme-linked immunosorbent assay (ELISA). There is a major advantage for combination of electrospun fibers and copolymers. Fiber structre of electrospun PHB provides large specific surface area available for biomolecular interaction. In addition, polymer coated parts of the platform inherited the premanent presence of surface carboxyl (-COOH) groups from MAA segments of the copolymer which can be effectively used for covalent and physical protein immobilization. By tuning the concentration of MAA monomers in polymerization reaction the concentration of surface -COOH groups can be carefully controlled. Therefore two different techniques have been used for immobilization of the dengue antibody aimed for dengue detection: physical attachment of dengue antibodies to the surface and covalent immobilization of antibodies through carbodiimide chemistry. In that perspective, several different characterization techniques were employed to investigate the new polymeric fiber platform such as scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (WCA) measurement and UV-vis titration. Regardless of the immobilization techniques, substantially higher signal intensity was recorded from developed platform in comparison to the conventional ELISA assay.

D.s.c. studies of the reaction between epoxidized natural rubber and benzoic acid

Abstract The reactions between epoxidized natural rubber (ENR) and benzoic acid have been investigated at elevated temperatures, in the range 398–433 K, by differential scanning calorimetry (d.s.c.). The reaction is characterized by a significant increase in the glass transition temperature ( T g ) of the material, the increase being proportional to the amount of added acid. The kinetics of the reaction have been elucidated by monitoring the rate of change of T g with respect to the reaction time as well as by direct measurements of the enthalpy change of reaction. The reaction is found to be first order with respect to benzoic acid and to have an overall activation energy of 70 kJ mol −1 . 13 C nuclear magnetic resonance studies employing 13 C-enriched benzoic acid showed that the benzoic acid was rapidly incorporated into the polymer main chain with the formation of ester linkages. Secondary, slower reactions were also in evidence but have not been positively identified. The incorporation of benzoic acid leads to a T g elevation of about 3.7 K mol% −1 modification and suggests that such reactions might prove useful in changing the physical properties of such rubbers. The significant elevation of T g associated with ENR vulcanized by dibasic acids is probably predominantly due to the modified main chain structure rather than the crosslinking network.

Determination of epoxy groups in natural rubber by degradation methods

Abstract The degradation of acid hydrolysed natural and epoxidized synthetic rubbers with lead tetraacetate and periodic acid have been studied, viscometrically. The epoxy content calculated from the degradation experiments is very much lower than that determined by a direct titration method. The discrepany is attributed mainly to incomplete hydrolysis of the rubber epoxides. The results demonstrate that the epoxy content of natural rubber is predominantly located on the rubber backbone.

Distribution of abnormal groups in natural rubber

Abstract Fresh samples of natural rubber were fractionated and the distribution of epoxy and amine groups over the molecular weight range was investigated. The origin of these abnormal groups is suggested. A scheme is proposed to explain the formation of lactone groups from the reaction products of the rubber epoxide and simple amino-acids. The presence of other functional groups is discussed.

Hydrogenation of natural rubber using nickel 2-ethylhexanoate catalyst in combination with triisobutylaluminum

Kinetic studies for the homogeneous hydrogenation of natural rubber, in the presence of nickel 2-ethylhexanoate and triisobutylaluminum, have been carried out by monitoring the change in hydrogen pressure in a Parr reactor of fixed volume. 1H-NMR spectroscopy provides the measurements of the extent of hydrogenation. The reaction kinetics, in the presence of a fixed amount of catalyst, showed an overall second-order kinetic with respect to [H2] and [CC]. The reaction has a relatively low apparent activation energy of 26.0 kJ mol-1 and is therefore suitable for the hydrogenation of natural rubber at ambient conditions to minimize side reactions. The impurities in commercial rubbers have a slight effect on the catalyst activity.