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Part 1 - The Drying of Natural Rubber: This was the initial research programme to be carried out at the Institute of Polymer Technology as a result of renewed interest in the area following information feed-back from the natural rubber consumers indicating a problem of wet rubber contamination. However, due to the difficulty in producing an acceptable starting material, the work had to be terminated with the compilation of what had been achieved including the literature survey, trials to produce a representative field latex coagulum, dewatering, diffusion and absorption experiments. Part 2 - Further Studies of the Stress Relaxation Behaviour of Rubber in Compression: With the development of stress relaxation measuring equipment at the Institute of Polymer Technology, highly accurate and reproducible results were obtained from the 'ideal curves'. This equipment not only provides measurement of residual force and the instantaneous modulus of a sample but also enables the whole process from 'loading' to the measurement of subsequent relaxed stresses to be made.

A number of simultaneous interpenetrating polymer networks (IPNs) were investigated with regard to morphology and energy absorbing ability. The materials were all based on polyurethane (PUR) with the second polymer components being polystyrene (PS) or poly(ethyl methacrylate) (PEMA). Also, three-component IPNs were synthesised. This was achieved by incorporating functionalised PS latex particles into a PUR/poly(butyl methacrylate) (PBMA) IPN. The morphology of the IPNs was determined with dynamic mechanical thermal analysis (DMTA), transmission (TEM) and scanning (SEM) electron microscopy and modulated-temperature differential scanning calorimetry (M-TDSC). The mechanical properties were investigated using tensile testing and hardness measurements. The PUR/PS IPNs were found to be grossly phase separated at every composition, even when crosslinked at very high levels. However, a structural modification of the materials was conducted by introducing inter-network grafting, compatibilisers and ionic interactions. All three structure modifications proved successful in achieving a finer morphology. By conducting a stirred synthesis, a very complicated morphology with a very high and broad transition was obtained. The PUR/PEMA IPNs were semimiscible and the 70:30 composition exhibited a very broad, almost rectangular, transition as evidenced by DMTA data. Phase domains between I - 500 run were found by TEM. The degree of mixing and, thus, the location and breadth of the transition could be adjusted by varying the composition and the crosslink densities in both networks. Also, variation of the chemical nature of the PUR soft and hard segments proved successful in obtaining a broad transition range. Materials with a controlled microheterogeneous morphology which exhibited excellent energy absorbing characteristics were developed. PUR/PEMA IPNs generally exhibited better damping properties as indicated by the area under the linear loss modulus (LA) and loss factor (TA) curves. Some of these materials exhibited values for the loss factor of >- 0.3 spanning a temperature range of more than 170°C. The study of IPN s containing latex' particles revealed promising results. Further concentrating on this approach might yield damping materials with even broader energy absorbing temperature/frequency ranges.

This research work was carried out to investigate the effect of unregenerated short cellulose fibres from woodpulp on the properties of rubber vulcanisates. It was also an objective of this work to find the type of woodpulp which was able to produce short fibre-rubber composites of good physical properties at a reduced cost. A screening procedure was carried out to identify one particular type of woodcellulose short fibre for detailed investigation. Mechanical woodpulps containing short cellulose fibres were selected based on their dispersibility properties in rubber, low cost, and universatility of application. Among various types of bonding agents studied, a resorcinolhexamethylenetetramine (RH) system was found to be most effective to bond woodcellulose fibre (mechanical type) to natural rubber -matrix. This was judged by certain properties namely, restricted equilibrium swelling, yield stress and tear strength. Restricted equilibrium swelling in particular was established to be a very useful technique by which the degree of adhesion can be predicted. In-this technique, the short fibre-rubber composites were swollen in toluene. for one week, after which, the volume restriction value, Vr was calculated using the following formula: Vr= (VI - VF)/VI, where VI and VF are the volume fraction of rubber in dry and swollen samples respectively. Based on Vr value, it has been observed that, with the exception of silane, all bonding systems studied improved woodcellulose fibre-natural rubber adhesion. Optimisation work to determine the optimum level of resorcinol-hexamethylenetetramine combination was also carried out based on a statistical factorial experimental design, in particular the 'central composite design'. Contour graphs of different properties of compounds for various levels of bonding agent combination were obtained by means of computer programmes. From these contour graphs it has been established that the 3 parts of hexamethylenetetramine (HMT) and 4 parts of resorcinol combination gives the best overall properties. Mechanical properties of composites containing optimum level of resorcinol-HMT combination measured in the direction of fibre orientation have indicated their dependence on fibre concentration. Young's modulus in particular increases exponentially with increasing fibre concentration. Experimental and theoretical curves of Young's modulus versus volume concentration of fibres show good correlation up to fibre volume concentration of 30%; beyond which increasing divergence occurred. Besides physical and mechanical properties, the cost factor of woodcellulose fibre-rubber composite is also considered. Cost advantage is clearly evident as a result of incorporation of woodcellulose fibre in natural rubber compound.

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Four SBS block copolymers were subjected to extensive chemical examination to determine block molecular weights and styrene fractions. Casting from different solvent systems into sheet form resulted in a range of microstructural formations for the normally dispersed styrene phase. These morphological details were studied using transmission electron microscopy and low angle X-ray scattering. Dynamic mechanical tests, on sheet material cast from different solvent systems, in both shear and tension over a wide temperature range, and static tensile tests at +20°C, revealed significant differences in viscoelastic properties between the materials. These differences were related to changes in morphological detail by the use of a model for composite materials. The large strain behaviour at +20°C is modelled by the inverse Langevin function and a debonding parameter which is related to void growth in the material. The conventional analysis of tear behaviour, developed originally for vulcanised rubbers, whilst ranking SBS block copolymers alongside the most tear resistant vulcanised materials over wide ranges of temperature and tearing rate, was found to be suspect for this class of materials. An alternative interpretation, however, succeeds in relating tear strength to tensile properties for the temperatures and tear rates studied, and also relates the tearing behaviour of these elastomers to that of a wide variety of other materials.

An attempt has been made to evaluate the kinetics of the thermal and combined thermal/radiative degradation of a peroxide cured polydimethylsiloxane elastomer (PDMS), and a vinylidene fluoride-hexafluoropropylene elastomer (Viton E60-C),by chemical stress relaxation measurements. It was observed that the PDMS elastomer degraded thermally by hydrolytic scission of the main chain and chain reformation by condensation of the silanol chain end groups. However,predominant chain reformation was observed during thermal degradation studies and it was believed that this was a consequence of the reformation of chains cut during the test,and also the reformation of chains cut prior to the test in the post cure operation. These two components of the observed chain reformation response were subsequently rationalized by a model. Thermal degradation of the Viton E60-C elastomer appeared to take place by hydrolytic scission of the amine crosslinkages, and subsequent crosslink reformation by condensation,indicating that the material had not been subjected to a suitable post cure treatment in order to remove water generated by the vulcanization reaction. At temperatures above 200°C predominant crosslinking was observed and this was attributed to the presence of a concurrent reaction which leads to the formation of ring structures. Thermal/radiative degradation studies indicated that temperature and radiation had a synergistic effect on the overall rate of induced chain scission in the PDMS elastomer but the mechanisms responsible for this phenomenon have yet to be established.

Current stress relaxation measurements in compression and the associated equipment are not reliable enough to carry out prolonged tests, especially at high temperatures and in liquid environments. The methods of measurement are outlined with the greatest flexibility in BS 903 Part 34, yet the consideration given to overcome the difficulties encountered is limited. The objectives of this sponsored programme were to examine the best available equipment, to generate a set of accurate data including some at relatively high temperatures; and to formulate a technique to extrapolate these high temperature results to service temperatures.

Cationic surfactants of general structure [RNH2(CH2)3NH3]2+ 2[R'COO]- can be used in rubber processing as multifunctional additives (MFA) which act as processing aids, accelerators and mould release agents. The effects of MFA on gum rubber, carbon black and silica filled compounds were investigated and attempts have been made to explain the mechanism of their action. This was done by studying mixing, vulcanisation behaviour, rheology, and mould release. The principal MFA used was Akzo-Nobel EN444.