Adisai Rungvichaniwat

The influence of mixed conventional sulfur/peroxide vulcanization systems on the mechanical and thermal properties of natural rubber/polypropylene blends

The role of mixed conventional sulfur/peroxide vulcanization systems on the mechanical and thermal properties of natural rubber/polypropylene thermoplastic vulcanizate (TPV) was investigated. Various proportions of peroxide in the mixed vulcanization system were used to dynamically vulcanize the natural rubber phase in the blend. The results show that using a mixed vulcanization system results in TPVs with superior properties in all areas studied, to those of TPVs cured by individual sulfur or peroxide systems. However, the peroxide content in the mixed vulcanization system has a strong effect on the variation in properties. A system containing 30 parts of peroxide to 70 parts of sulfur, results in a TPV with the best overall properties due to a balance of the effects of the sulfur and the peroxide curing agents in the blend. This ratio promotes optimum cross-link density, cross-link patterns, and low competing reactions of the peroxide and co-agents. As a result, improvements in the mechanical and thermal properties of the TPV are obtained with 30 parts of peroxide in the mixed system. Any further increase in the peroxide content results in a deterioration of those properties due to inefficient cross-linking with a high degree of competing reactions. Thus, close attention should be paid to the ratio of sulfur to peroxide or more specifically to the content of peroxide when selecting a mixed vulcanization system as a cross-link agent.

Waterborne Polyurethane: Effect of Functional Groups in Aromatic Isocyanate and the Chain Length of Hydroxyl Terminated Natural Rubber

Waterborne polyurethane (WPU) has its main applications in coatings and adhesives. Compared with the competing PU products from solvent-based processes, it has a more environmentally friendly manufacturing process. Its economic competitiveness could also be improved by the use of aromatic isocyanates that are widely available and cheaper than the currently used aliphatic isocyanates. We report on the synthesis and properties of WPU, based on natural rubber (NR) whose molecular structure has been altered, in combination with an aromatic isocyanate. The NR modification is by hydroxyl termination, with experiments using two chain lengths (HT600 and HT1000, named after molecular weight). The aromatic isocyanates used are 4,4’-Methylene bis (phenyl isocyanate) (MDI) and polymethylene polyphenyl polyisocyanate (p-MDI). The synthesized chemical structure is characterized using ATR-FTIR, while the key material properties reported here are the pH value, mean particle size and size distribution, and glass transition temperature. The WPU achieved suitable material properties, with small particles sizes and good dispersion, for applications in coatings.

Novel Creaming Agent for Preparation of Creamed Concentrated Natural Rubber Latex

Creaming process with a novel creaming agent, hydroxyl ethyl cellulose, and ammonium laurate soap is performed. It has been found that the total solid content and dry rubber content of creamed latex are 64.33% and 63.31%, respectively. Latex properties of the creamed latex are examined and compared with that of centrifuged latex. It has been found that most properties are similar, except that extractable protein content, mechanical stability time, and viscosity of the creamed latex are higher than that of the centrifuged latex. Furthermore, the creamed latex exhibits larger particle size with broader particle size distribution than that of the centrifuged latex.

The examination of the structure property relationships of some water-dispersed polyurethane elastomers

Water-dispersed or latex polyurethanes (PUs) have been known for many years. However, in the last decade there has been an increased level of R&D interest into these types of polymers, with potential use as coating and adhesive materials. In part, this research has been driven by the introduction of laws and regulations intended to reduce and eliminate the use of organic solvents, and so to minimise environmental pollution. Latex or emulsion forms of PUs have been investigated because of their specific end-use properties, in particular excellent adhesion and long term barrier properties. This paper reports a study of some experimental formulations of water-dispersed polyurethanes based on tetramethylxylene diisocyanate (TMXDI), some polyesterols or polyetherols polyols and an aliphatic diamine chain extender. These have been synthesised as water dispersions, with dimethylol prioponic acid and triethylamine used as providing anionic centres and neutralising agent, respectively in the aqueous phase. Some properties of the various formulations as dispersions were determined, including particle size, surface free energy, viscosity and dispersion stability. Stable dispersions were subsequently converted into coherent, dry, thin sheet materials, which were characterised using thermal analysis and some mechanical test methods. The research has shown it is possible to produce stable water-dispersed urethane-urea copolymers, based on different molar masses of polyesterol or polyetherol precursors and TMXDI, and also where hard segment content was varied (i.e. by different ratios of combined dialcohol species to diamine). It was found that stable dispersions can be made with a broad range of internal emulsifier content in the polymer chain, that have low viscosity and low surface free energy. Particle size of the polymer dispersions was affect by emulsifier content: higher levels producing small particles. At low levels of emulsifier, the stability of the dispersions was increasingly poor, while at higher levels, viscosity increased due to small particle size and increasing coulombic effects. Stable dispersions cast into thin dry films of coherent elastomers, have good mechanical properties, similar to those of urethane-urea copolymers synthesised by water-free methods. Thermal analysis suggests that the degree of phase mixing of hard and soft segment in these polymers, parallels that reported for to urethane-urea copolymers synthesised by water-free methods.

Influence of Processing Oil Based on Modified Epoxidized Vegetable Oil with N-Phenyl-p-Phenylenediamine (PPD) on Extrusion Process Behaviors of Natural Rubber Compounds

Rubber processing oil based on modified epoxidized vegetable oils (m-EVO) was prepared by a reaction of epoxidized palm oil EPO) or epoxidized soybean oil (ESBO) with N-Phenyl-ρ-phenylenediamine (PPD) at a mole ratio of 1:0.5. The comparison of m-EVO with aromatic oil (Treated distillate aromatic extract, TDAE) on extrusion process behaviors (output rate, extrusion rate, screw efficiency, heat generation, die swell, extrudate appearance) of carbon black (N330) filled natural rubber (NR) compound was made. It was found that the mooney viscosity of m-EVO based natural rubber compounds are slightly higher than that of the TDAE based natural rubber compound (ML(1+4)100°C: m-ESBO 65.5±0.7; m-EPO 59.7±0.2; TDAE 56.5±1.0), which probably due to the poorer filler dispersion in the compounds. The extrusion process behaviors for output rate (g/min: m-ESBO 191.0±0.6; m-EPO 191.2±0.4; TDAE 195.5±0.6), extrusion rate (cm3/min: m-ESBO 179.6±0.6; m-EPO 183.2±0.4; TDAE 186.4±0.6) and screw efficiency (%: m-ESBO 30.8±0.6; m-EPO 31.4±0.4; TDAE 32.0±0.6). All the three compounds show similar extrusion process behaviors in which the TDAE based compounds shows a marginal higher values than the m-EVO as its lower mooney viscosity lead to a better flow. The m-EPO and m-ESBO based natural rubber compounds show very similar extrusion process behaviors. The heat generation (°C: m-ESBO 61.0±0.8; m-EPO 62.1±0.4; TDAE 63.1±1.0) and die swell (%: m-ESBO 11.0±0.7; m-EPO 11.0±0.5; TDAE 12.7±0.3) of the m-EVO based natural rubber compounds are slightly lower than those of the TDAE based natural rubber compound. As there are no significant differences in the extrusion process behaviors, with respect to extrusion process, m-EVO can be used to replace TDAE oil.

Effect of Various Extracted Solvent on DPPH Radical Scavenging Activity of Natural Rubber

Four types of extracted solvents i.e. mixtures of chloroform:acetone, chloroform:methanol, cyclohexane:acetone and cyclohexane:methanol, in the volume ratio of 4:1 were used to dissolve the natural rubber. Two grades of natural rubber i.e. air dry sheet (ADS) and ribbed smoked sheet No.3 (RSS3) were investigated. The rubber solution was purified by separated the rubber out with methanol. The non-rubber solution was then quantitative analyzed to verify 2,2-diphenyl-1-picryhydrazyl (DPPH) radical scavenging activity using Oxicount-Antioxidant kit test and also calculated the term of half maximal effective concentration (EC50). The plasticity retention index (PRI) was also investigated in order to compare the ageing properties of the rubber and their antioxidant activity. Furthermore, various rubbers i.e. ADS, RSS3 and Standard Thai Rubber 20 (STR20) were collected during early period of yearly tapping seasons to analyze the DPPH radical scavenging activity and EC50. It was found that the mixture of cyclohexane and methanol showed the highest DPPH radical scavenging activity and lowest EC50. RSS3 showed higher DPPH radical scavenging activity than that of ADS which the higher antioxidant activity also displayed the higher PRI values. It also found that during the early period of yearly tapping seasons, DPPH radical scavenging activity of RSS3 was found higher than that of ADS and STR20, respectively when extracted by mixture of cyclohexane and methanol.

Color and Antioxidant Changes in Various Natural Rubber Processes

Fresh field natural rubber was coagulated by acetic acid, soaked in water at room temperature (WRT) or 70°C (W70) for 1 hr, and then dried in an oven at 40°C. Non-soaked natural rubber samples (NoW) served as a control. Two grades of natural rubber, namely air-dry sheet (ADS) and ribbed smoked sheet No.3 (RSS3) derived from the same latex, were also investigated. All dry rubber samples were characterized with Lovibond colorimeter according to ASTM D3157, as well as with a HunterLab spectrophotometer. Furthermore, all the dry rubber samples were dissolved in a chloroform:methanol mixture (4:1 v:v). The rubber was then precipitated out of the solution with methanol, and the remaining solution was quantitatively analyzed for total phenolic content (TPC). The plasticity retention index (PRI) was determined for all the dried rubber samples according to ASTM D3194. It was found that WRT, W70 and ADS were similar in lightness L*, while RSS3 had the lowest L*. W70 had the lowest redness a*, which increased in the order WRT, NoW, RSS3 and ADS. W70 also had the lowest yellowness b*, which increased in the order RSS3, NoW and WRT and ADS. Moreover, TPC was the lowest for the W70 sample, increasing in the order ADS, WRT, NoW and RSS3. The PRI was highest for W70, and decreased in the order WRT, RSS3, NoW and ADS. All of the PRI values observed were comparatively high relative to blocked standard Thai rubber 20 (STR20).

Influence of Zinc Oxide Contents on Mechanical, Rheological and Thermal Properties of Thermoplastic Natural Rubber

The influence of ZnO contents on properties of the natural rubber/polypropylene thermoplastic vulcanizates (NR/PP TPVs) is investigated. The NR/PP TPVs with ZnO obviously show improvement of mechanical, rheological and thermal properties comparing to the TPV without ZnO addition. The ZnO content does not much affect on mechanical and rheological properties of the TPVs. However, it strongly influences on thermal property especially decomposition temperatures at 5 and 50 %wt loss of polymer (Td5 and Td50) and onset decomposition temperature of rubber phase (Tronset).