Jitladda Sakdapipanich

Characterization of associated proteins and phospholipids in natural rubber latex

Non-rubber components present in natural rubber (NR) latex, such as proteins and phospholipids, are presumed to be distributed in the serum fraction as well as surrounding the rubber particle surface. The phospholipid-protein layers covering the rubber particle surface are especially interesting due to their ability to enhance the colloidal stability of NR latex. In this study, we have characterized the components surrounding the NR particle surface and investigated their role in the colloidal stability of NR particles. Proteins from the cream fraction were proteolytically removed from the NR latex and compare to those from the serum fractions using SDS-polyacrylamide gel electrophoresis revealing that both fractions contained similar proteins in certain molecular weights such as 14.5, 25 and 27 kDa. Phospholipids removed from latex by treatment with NaOH were analyzed using (1)H-NMR spectroscopy and several major signals were assignable to -(CH(2))(n)-, -CH(2)OP, -CH(2)OC═O and -OCH(2)CH(2)NH-. These signals are important evidence that indicates phospholipids associate with the rubber chain. The colloidal behavior of rubber lattices before and after removal of protein-lipid membrane was evaluated by zeta potential analysis and scanning electron microscope (SEM). The lowest zeta potential value of NR particles was observed at pH 10, consequently leading to the highest stability of rubber particles. Additionally, SEM micrographs clearly displayed a gray ring near the particle surface corresponding to the protein-lipid membrane layer.

Strain-induced Crystallization of Natural Rubber: Effect of Proteins and Phospholipids

Abstract The effects of proteins and phospholipids in natural rubber (NR) on the strain-induced crystallization behavior during uniaxial deformation were studied by in-situ synchrotron wide-angle X-ray diffraction (WAXD) technique and simultaneous measurements of stress-strain relation. The influences of proteins and phospholipids in NR were evaluated separately by decomposition methods using deproteinization and lipase treatment, respectively. It was found that both components form a naturally occurring network, which is responsible for the strain-induced crystallizability of unvulcanized NR and the corresponding high mechanical property. This network also plays a significant role in strain-induced crystallization of vulcanized natural rubber.

Effect of Gel on the Green Strength of Natural Rubber

Abstract The outstanding properties of natural rubber, e.g., green strength and rapid crystallization, were attributed to the chemical branching that formed at both chain ends of the rubber molecule during the preservation of the latex in the presence of ammonia. The gel content of natural rubbers from various clonal origins increased during the preservation, but decreased after deproteinization of the aged latex. The crystallization of acetone-extracted rubber was slightly suppressed as the gel content increased. The increase in green strength during the preservation was studied in connection with the gel content and degree of branching of the rubber.

Characterization of fatty acids linked to natural rubber-role of linked fatty acids on crystallization of the rubber

Abstract Natural rubber isolated from Hevea brasiliensis contains two types of long chain fatty acids: fatty acids linked to rubber chain at the chain-terminal and those present as a mixture. The composition and role of these fatty acids were characterized by 1 H NMR spectroscopy, gas chromatography and differential scanning calorimetry. The linked fatty acids were composed of saturated and unsaturated C 10 –C 22 fatty acids, the composition of which was similar to that of mixed fatty acids. As models of natural rubber, fatty acid groups, such as decanoyl (C 10 ), myristoyl (C 14 ) and stearoyl (C 18 ), were esterified to synthetic cis -1,4-polyisoprene (IR) selectively at 3,4 isomeric units, by hydroboration followed by esterification with acyl chloride. The acceleration effect of linked fatty acids on the crystallization behavior was analyzed for these models and natural rubber. The IR linked with myristoyl group showed the most rapid crystallization at −25°C among the samples prepared, as it was mixed with palmitic acid. This was explained to be due to the nucleating effect of saturated fatty acid and plasticizing effect of unsaturated fatty acid for the polymer.

Cloning and characterization of farnesyl diphosphate synthase from the rubber-producing mushroom Lactarius chrysorrheus.

Farnesyl diphosphate is involved in rubber biosynthesis as an initiating substrate for both polyprenol and mushroom rubber. So far, we have isolated the cDNA of a farnesyl diphosphate synthase (FPS) for the first time from a rare rubber-producing mushroom, Lactarius chrysorrheus, by the degenerate RT-PCR technique based on sequence information of FPS genes from fungi and yeasts. The open reading frame was clarified to encode a protein of 381 amino acid residues with a calculated molecular weight of 42.9 kDa. The deduced amino acid sequence of L. chrysorrheus FPS showed about 50% identity with those of other fungi and yeasts as well as plants. We expressed the cDNA of L. chrysorrheus FPS in Escherichia coli as a glutathione-S-transferase (GST)-fusion protein. The purified obtained protein showed FPS activity in which geranyl diphosphate (GPP) served as primary substrate, with a 2.4-fold higher kcat⁄Km value for GPP than for dimethylallyl diphosphate (DMAPP).

Depolymerization and ionic conductivity of enzymatically deproteinized natural rubber having epoxy group

Abstract Preparation of liquid epoxidized natural rubber (ENR) was made by oxidative depolymerization of ENR in latex stage without loss of epoxy group. Epoxidation of fresh natural rubber latex, which was purified by deproteinization with proteolytic enzyme and surfactant, was carried out with freshly prepared peracetic acid. The glass transition temperature ( T g ) and gel content of the rubbers increased after the epoxidation, both of which were dependent upon an amount of peracetic acid. The gel content was significantly reduced by oxidative depolymerization of the rubber with (NH 4 ) 2 S 2 O 8 in the presence of propanal. The resulting liquid epoxidized rubber ( M n ≈10 4 ) was found to have well-defined terminal groups, i.e. aldehyde groups and α-β unsaturated carbonyl groups. The novel rubber was applied to transport Li + as an ionic conducting medium, that is, solid polymer electrolyte.

Molecular dynamics of natural rubber as revealed by dielectric spectroscopy: The role of natural cross–linking

In order to understand the molecular dynamics of natural rubber, the dielectric relaxation behavior of its different components were investigated. These components included: (1) the linear polyisoprene fraction, obtained after deproteinization and transesterification of natural rubber (TE–DPNR), (2) the gel (GEL) fraction, corresponding to pure natural chain–end cross–linked natural rubber, (3) deproteinized natural rubber (DPNR), in which the protein cross–links at the ω–end have been removed, and (4) natural rubber (CNR) purified (through centrifugation) but still containing proteins, phospholipids and the sol phases. The dielectric relaxation behaviour of natural rubber revealed a segmental mode (SM) which is not affected by natural chain-end cross-linking (so-called naturally occurring network) and a normal mode (NM) which depends on a naturally occurring network. The dynamics of the NM, which is associated to chain mobility, seems to be strongly affected by natural chain-end cross-linking. We propose a model based on a hybrid star polymer in which the low mobility core (phospholipids) controls the mobility of the polyisoprene arms.

Effect of non-rubber components on storage hardening and gel formation of natural rubber during accelerated storage under various conditions

Abstract The phenomenon of storage hardening in solid natural rubber (NR) is presumed to occur by means of reactions between some non-rubber components and abnormal groups in rubber molecule. The main non-rubber constituents in NR are composed of proteins and lipids. The storage hardening behavior of NR purified by enzymatic deproteinization and transesterification was analyzed under high and low humidity conditions using phosphorus pentoxide (P2O5) and sodium hydroxide (NaOH). The NR obtained from centrifuged fresh natural rubber latex (CFNR) and deproteinized NR latex (DPNR) showed significant increase in the hardening plasticity index (PH) value during storage; while that of the transesterified NR (TENR) and transesterified DPNR (DPTE-NR) was almost constant during storage. After keeping samples under high humidity conditions, the fresh natural rubber (FNR), CFNR and DPNR showed constant PH value, while that of the TENR and DPTE-NR decreased during storage. The FNR, CFNR and DPNR showed a clear increas...

Structural Characterization of Terminal Groups in Natural Rubber: Origin of Nitrogenous Groups

Abstract The nitrogenous groups in natural rubber (NR) from Hevea brasiliensis have been regarded as an important factor governing cured rubber properties, although there is no structural evidence. The nitrogenous compounds in highly purified NR were characterized to disclose the origin of nitrogenous groups. The rubber particles in fresh latex were purified by washing, i.e., successive dilution of the cream fraction and concentration by centrifugation in the presence of surfactant. The nitrogen content of natural rubber from the washed rubber particles decreased from 0.281% to 0.015% level after washing 3–5 times, the level of which was similar to that of deproteinized natural rubber with a proteolytic enzyme. The presence of 1–2 nitrogen atoms per rubber chain was presumed based on the nitrogen content and Mn value. The nitrogen content of fractionated rubber fractions from rubber particles washed 5 times increased with increasing molecular weight. The nitrogenous group in the rubber chain is postulated...

Crystallization behavior and strength of natural rubber: Skim rubber, deproteinized natural rubber, and pale crepe

Crystallization behavior of natural rubber prepared by different procedures, such as skim rubber, deproteinized natural rubber (DPNR), and pale crepe, was investigated by dilatometry at −25°C. DPNR was fractionated into four fractions by molecular weight. The high molecular weight fractions contained about 1.7 linked fatty acids per rubber molecule, while low molecular weight fraction showed an increase in quantity. The overall crystallization rate of the rubber decreased as the molecular weight decreased. Skim rubbers, purified by extraction with acetone, crystallized rapidly compared to acetone-extracted pale crepe, despite that the molecular weight of skim rubbers was about one-half of pale crepe. The quantity of linked fatty acid per rubber molecule of skim rubbers was less than 0.5, while that of pale crepe was 1.6. The difference in the rate of crystallization was presumed to be associated with the level of fatty acids linked to rubber molecule at the terminal and branch points present in pale crepe. The green strength of skim rubbers was significantly lower than those of untreated pale crepe and DPNR, but was comparable to transesterified DPNR, which contains no gel fraction and no linked fatty acids.