Azanam S. Hashim

The Effect of Bis(3-Triethoxysilylpropyl) Tetrasulfide on Silica Reinforcement of Styrene-Butadiene Rubber

Abstract Bis(3-triethoxysilylpropyl)tetrasulfide (TESPT) was found to affect the curing characteristics and the physical properties of styrene-butadiene (SBR) gum rubber and xin situ silica-filled SBR vulcanizates. Silica incorporated by the in situ sol-gel reaction of tetraethoxysilane with TESPT showed a much higher reinforcing efficiency than did conventional mechanical mixing and the in situ method without TESPT. The higher reinforcing efficiency is attributed to the formation of a silica-rubber network, which also changed the dynamic mechanical behavior of the SBR vulcanizates. Transmission electron microscopy observations showed in situ silica incorporation of very fine particles in comparison to the sol-gel process without TESPT.

Developments of high performance vibration absorber from poly(vinyl chloride)/chlorinated polyethylene/epoxidized natural rubber blend

A high performance vibration absorber requires a high loss factor behavior over a wide temperature and frequency range. An investigation was carried out to prepare such materials based on poly(vinyl chloride), chlorinated polyethylene, and epoxidized natural rubber ternary blends. The loss factor and damping behavior of several compositions were measured using a viscoelastic spectrometer and a polymer-laminated steel cantilever-beam damping device. Suitable compositions were found to give good mechanical properties and high loss factor over a wide temperature and frequency range. It was also observed that flake-type fillers improve the damping behavior.

Silica reinforcement of epoxidized natural rubber by the sol-gel method

The sol-gel technique was employed to prepare silica-reinforced vulcanizates using tetraethylorthosilicate (TEOS) and epoxidized natural rubber (ENR). The rubber was first precured with 3-aminopropyltriethoxysilane (APS) by heat pressing at 180°C for a range of cure time. The resultant rubber sheets or vulcanizates were swelled in TEOS, and subsequently subjected to a sol-gel reaction in butylamine aqueous solution. Hydrolysis and condensation of the TEOS resulted in the formation of silica particles in the rubber network yielding silica-contained vulcanizates. Silica content as high as 28% and TEOS-to-silica conversion of over 60% were observed. When prepared under certain reaction conditions, the sol-gel vulcanizates obtained were more rigid and stronger than a typical sulfur-cured ENR vulcanizate that contained comparable amount of silica. Comparative stress-strain and dynamic mechanical property analysis suggest that chemicals bond are formed between the silica particles and the rubber network in the ENR-APS-sol-gel vulcanizate. Thus, the “in situ” silica reinforcement of ENR was successfully established.

An investigation of the potential of rice husk ash as a filler for epoxidized natural rubber—II. Fatigue behaviour

Abstract The fatigue behaviour of white rice husk ash (WRHA) filled ENR-50 vulcanisate was compared with those of silica and carbon black filled ENR-50. The effects of the silane coupling agent (δ-mercaptopropyltrimethoxysilane, vulcanisation systems, hysteresis and the failure mode of the vulcanisates were studied. It was found that the incorporation of fillers reduced the fatigue life of vulcanisates, while silica filled ENR vulcanisates showed the best fatigue life followed by WRHA, then carbon black filled vulcanisates. The coupling agent improved fatigue life with a simultaneous reduction in WRHA filler aggregates and improved filler dispersion for all vulcanisates. Conventional vulcanisation systems gave the highest fatigue life followed by semi-efficient and then efficeint vulcanisation systems. Carbon black filled ENR vulcanisates showed the highest hysteresis as indicated by the strain exponent. The failure mode was found to be of a dual nature.

Study of two types of styrene butadiene rubber in tire tread compounds

Abstract The ratio of vinyl butadiene and styrene groups in styrene butadiene rubber (SBR) structures is a crucial factor that affects the inherent rubber characteristics such as glass transition temperature, Tg, hysteresis, strength, etc. In this paper, two types of SBR (Krynol 1721 and Buna VSL 5025-1) which contain higher ratios of these two groups, were blended with natural rubber (SMR 5) and compared with a blend of general purpose SBR (Krynol 1712) and SMR 5. The results show that the blends with the two rubbers possess a markedly lower resilience (i.e. higher hysteresis) than that of the general purpose SBR. Besides resilience, other properties of the compounds, Mooney viscosity, scorch time, cure time, tensile strength, tear strength, and ageing resistance were also investigated. At a similar blending ratio of 50:50, blends with Krynol 1721 and Buna VSL 5025-1 show markedly lower rebound resilience while other mechanical properties are considered acceptable. This preliminary investigation indicates that the two rubbers are suitable for wet grip improvement. Subsequently, the ratio of Krynol 1721 and Buna VSL 5025-1 in the blends was varied from 30 to 70 phr. As the ratio of the rubbers is increased, a reduction in rebound resilience is also observed and the effect of Buna VSL 5025-1 is more pronounced than Krynol 1721. The result is consistent with the higher Tg of the former. Mooney viscosity, scorch time, cure time and ageing index (based on tensile strength) are increased but there is a slight drop in tensile strength and tear strength.

A Comparative Study of Styrene Polymerization in Deproteinized and Undeproteinized Natural Rubber Latex

Abstract An investigation on in situ polymerization of styrene in deproteinized natural rubber (DPNR) latex and high ammonia natural rubber (HANR) latex was carried out. The ratio of styrene to dry rubber was fixed at 25 : 75 by weight. It was observed that, at reaction temperature of 60 °C and reaction time of 10 hours, the styrene-DPNR system could attain a high conversion of 97% without adding surfactant. The degree of chemical bonding estimated for the resultant polystyrene-DPNR dried material was about 80%. The styrene-HANR system, however, required the addition of surfactant to complete the reaction time; but the conversion was found to be relatively low, in the region of 66%. This low conversion could be attributed to the role played by the protein/lipid layer, which is virtually absent in the styrene-DPNR system.

Preparation and properties of epoxidized natural rubber network crosslinked by ring opening reaction

Abstract A rubber network is prepared by reacting epoxidized natural rubber (ENR) with p-phenylenediamine. The ring opening crosslinking reaction was found to have an apparent activation energy of 67·5kJ/mole. Bisphenol A, a catalyst for the reaction, seems to reinforce the stress-strain properties of the network via hydrogen bonding interaction. Dynamic mechanical analysis and stress-strain measurement indicate that, in comparison to a typical ENR-sulfur network, the ENR-amine structure is more rigid and less stretchable at room temperature as demonstrated by its relatively high glass transition temperature and low rupture point. The ENR-amine network also demonstrates significantly lower tensile strength than the ENR-sulfur one although their crosslink densities are not significantly different. This behavior could be attributed to the formers lack of strain-induced crystallization which is a pronounced feature of the latter.

Effect of In Situ Polymerization of Styrene onto Natural Rubber on Adhesion Properties of Styrene-Natural Rubber (SNR) Adhesives

Styrene-based deproteinized natural rubber (SNR) latex was synthesized by in situ polymerization. Three pre-vulcanization systems [conventional-cured (CV), semi-efficient-cured (Semi-EV), and efficient-cured (EV)] were studied in terms of tensile and adhesion properties. Good tensile properties were observed for CV and EV SNR. The Semi-EV SNR showed the best adhesion properties based on the good anchorage performance in all substrate pairings (polystyrene–polystyrene, polystyrene–rubber, and rubber–rubber). The pH modification on SNR latex via KOH addition has beneficial effects of removing protein layers, resulting in more styrene grafting sites in the rubber molecules. Consequently, the tensile and adhesion properties of the SNR are improved as more styrene polymers are grafted onto the rubber matrix. Semi-EV SNR with pH 12 has superior adhesive performance; hence, it is suitable for use as a pressure-sensitive adhesive.

Preparation and properties of epoxidized natural rubber/poly(ε-caprolactone) self-vulcanizable blends

Curing behaviour as well as mechanical properties of the binary blends of epoxidized natural rubbers (ENR) with end-carboxylated telechelic poly(Iµ-caprolactone)s (XPCL) has been investigated for development of high-performance self-vulcanizable rubber blends. The binary blends of ENR with different degrees of epoxidation and XPCL of different molecular masses were prepared by using an open two-role mill and subsequently cured at 160–200 °C. It was found that the end-functional and crystallizable XPCLs cured ENR well in the absence of other additives and acted as an effective polymeric crosslinker for ENR to produce self-vulcanizable binary blends. The degree of chemical crosslinking depended on the degree of epoxidation of the ENR as well as the curing time and temperature. The relative contribution of the physical crosslinking via crystallization of poly(Iµ-caprolactone) chains to that chemical crosslinking was controlled by the molecular mass of the XPCL to give elastomeric materials with various stress–strain curves.

Comparison of the Different Vulcanization Techniques of Styrene Modified Natural Rubber (SNR) as an Impact Modifier of Natural Rubber-Based High Impact Polystyrene (NRHIPS)

Styrene modified natural rubber (SNR) is a modified rubber that can work as an impact modifier and compatibilizer for polystyrene (PS) matrix. The effect of different vulcanization techniques based on the sulfur vulcanization system has been investigated to produce SNR vulcanizates for natural rubber-based (NR) impact modifier for polystyrene. SNR is produced through emulsion polymerization of styrene monomer and deproteinized natural rubber (DPNR) latex. The styrene to DPNR ratio is 25:75 (wt/wt). SNR is vulcanized using sulfur vulcanization system with 1.5 phr sulfur loading for each blend. Each PS/SNR blend contains 20% rubber. Three different vulcanization techniques are proposed to produce SNR vulcanizates: mixed system ( in situ mixing together with physical mixing using two roll mills), in situ vulcanization, and physical mixing using two roll mills. PS/SNR blends show the in situ vulcanization process produce SNR vulcanizate, which gives the blends with better tensile properties and impact strength compared with the mixed system and physical mixing. The morphology in PS/SNR blends of PS/R1, PS/R2 and PS/R3 have further prove that SNR has better interaction with PS matrix compared with PS/*DPNR. PS/R3, which because they have in situ vulcanization SNR vulcanizate prepared by latex-based formulation, successfully produce SNR vulcanizates that can contribute as a natural rubber-based impact modifier.