The solid–liquidphase transition temperatures and heats of fusion ΔH f of nonpolar organic solids confined in the pores of controlled pore glasses were measured by differential scanning calorimetry. The pore diameters d were in the range of 40–730 A and the organics studied were cis‐decalin, trans‐decalin, cyclohexane, benzene, chlorobenzene, naphthalene, and heptane. In accordance with previous reports on studies of primarily inorganic materials, the melting point of the pore solidT(d) decreased with decreasing pore diameter. In addition, a large reduction in the bulk enthalpy of fusion ΔH f of the pore solid was measured, which apparently has not been studied in detail by other workers. A linear correlation was found between the melting point depression (ΔT m ) and the reciprocal diameter, as predicted by theories of solidification in a capillary. The calculated values of the solid–liquid interfacial energy σsl were in reasonable agreement with values reported in the literature based on other methods of measurement.

/pdf/the-melting-behavior-of-organic-materials-confined-in-porous-315yrxd5fm.pdf

The melting behavior of organic materials confined in porous solids

The study of preparing silica/rubber composites used in tires with low rolling resistance in an energy-saving method is fast-growing. In this study, a novel strategy is proposed, in which silica was modified by combing alcohol polyoxyethylene ether (AEO) and 3-mercaptopropyltriethoxysilane (K-MEPTS) for preparing silica/natural rubber (NR) master batches. A thermal gravimetric analyzer and Raman spectroscopy results indicated that both AEO and K-MEPTS could be grafted on to the silica surface, and AEO has a chance to shield the mercaptopropyl group on K-MEPTS. Silica modified by AEO and K-MEPTS together was completely co-coagulated with the rubber in preparing silica/NR composites using the latex compounding method with the help of the interaction between AEO and K-MEPTS. The performance of composites prepared by silica/NR master batches was investigated by a rubber process analyzer (RPA), transmission electron microscopy (TEM) and a tensile tester. These results demonstrate that AEO forms a physical interface between silica and rubber, resulting in good silica dispersion in the matrix. K-MEPTS forms a chemical interface between silica and rubber, enhancing the reinforcing effect of silica and reducing the mutual friction between silica particles. In summary, using a proper combination of AEO and K-MEPTS is a user-friendly approach for preparing silica/NR composites with excellent performance.

https://www.mdpi.com/2073-4360/10/1/1/pdf

Silica Modified by Alcohol Polyoxyethylene Ether and Silane Coupling Agent Together to Achieve High Performance Rubber Composites Using the Latex Compounding Method

The paper presents a phenomenological material model for a superimposed elastic–viscoelastic–plastoelastic stress response with damage at large strains and considers details of its numerical implementation. The formulation is suitable for the simulation of carbon-black filled rubbers in monotonic and cyclic deformation processes under isothermal conditions. The underlying key approach is an experimentally motivated a priori decomposition of the local stress response into three constitutive branches which act in parallel: a rubber–elastic ground–stress response, a rate-dependent viscoelastic overstress response and a rate-independent plastoelastic overstress response. The damage is assumed to act isotropically on all three branches. These three branches are represented in a completely analogous format within separate eigenvalue spaces, where we apply a recently proposed compact setting of finite inelasticity based on developing reference metric tensors. On the numerical side, we propose a time integration scheme which exploits intrinsically the modular structure of the proposed constitutive model. This is achieved on the basis of a convenient operator split of the local evolution system, which we decouple into a stress evolution problem and a parameter evolution problem. The constitutive functions involved in the proposed model are specified for a particular filled rubber on the basis of a parameter identification process. The paper concludes with some numerical examples which demonstrate the overall response of the proposed model by means of a representative set of numerical examples.

Superimposed finite elastic–viscoelastic–plastoelastic stress response with damage in filled rubbery polymers. Experiments, modelling and algorithmic implementation

From a study of silane coupling agents in reinforced plastics, a general mechanism of adhesion to hydrophilic mineral surfaces has been devised. According to this theory, adhesion of polymers to dissimilar surfaces is described as a dynamic equilibrium of making and breaking of adhesion bonds between polymer segments and the surface through the agency of a low molecular weight material—usually water. A dynamic equilibrium at the interface allows relaxation of thermal stresses. Water resistance results from a favorable equilibrium toward bonding through polar groups in the polymer. Silanol groups generally give optimum bonding to hydrophilic mineral surfaces. Such a dynamic mechanism of adhesion not only explains many complex adhesion problems of plastics to mineral surfaces, but also is compatible with the adhesion of ice, barnacles and tooth plaque to surfaces in an aqueous environment and with the requirements for rubber reinforcement by finely divided particulate fillers.

Adhesion Through Silane Coupling Agents

This essay investigates the temperature dependence of the mechanical properties of a filler-loaded tread compound experimentally and proposes a physically based method to represent this behaviour in the framework of non-linear continuum thermomechanics. To this end, we realise a series of monotonic and cyclic strain controlled tests on cylindrical specimens in tension at different temperature levels. The experimental data show the isothermal mechanical behaviour to be mainly influenced by non-linear elasticity in combination with non-linear rate dependence and weak equilibrium hysteresis. We observe that the rate sensitivity of the material depends strongly on the temperature : at low temperature levels, the rate sensitivity is essentially higher than at high temperatures. The elastic properties of the material depend comparatively less on the temperature. Nevertheless, higher temperature levels lead to higher equilibrium stresses. In order to represent the material behaviour, we start with a multiplicative split of the deformation gradient into a mechanical and a thermal part as proposed by Lu and Pister (1975). Physically, this idea corresponds to a stress-free thermal expansion followed by an isothermal stress-producing deformation. We suppose the thermal part of the deformation gradient to be isotropic. As a consequence of this, the velocity gradient decomposes additively into a pure thermal and a pure mechanical part. By using these elements, we exploit the Clausius Duhem inequality and assume the so-called ‘mechanical second Piola Kirchhoff stress tensor’ to be a functional of the ‘mechanical Green's strain tensor’. In a further step, we define this functional by a system of constitutive equations which are based on a rheological model. The evolution equations for the internal variables are formulated by using the concept of dual variables proposed by Haupt and Tsakmakis (1989, 1996). The rate sensitivity is modelled by a stress and temperature dependent viscosity function. The elastic part of the equilibrium stress is described by entropy elasticity in combination with a modified Mooney Rivlin strain energy function. The equilibrium hysteresis effects are represented by rate independent plasticity in arclength representation as proposed by Valanis (1971). The constitutive model is compatible with the dissipation principle of thermodynamics and describes the general trend of the experimental data fairly well.

On the large deformation behaviour of reinforced rubber at different temperatures

The interaction of carbon blacks with high polymers during the mixing process was studied by using fillers having a wide range of surface characteristics. Glass beads, Graphon, high-structure blacks, and heat-treated blacks were mixed with elastomers in the Brabender Plasticorder. With the use as a rubber matrix of a high polymer that did not materially change during the mixing process in molecular weight or viscosity, excellent correlation was found between final torque required for mixing and black structure and between peak torque and bound rubber. Increasing interaction was shown to lead to increased mixing torque, increased Mooney viscosity, increased modulus, and higher state of cure, as measured by swelling. If the high polymer matrix breaks down during the mixing process these influences of interaction are mostly obscured by diminishing molecular weight.

Carbon black–polymer interaction: A measure of reinforcement

Interaction between carbon black and polymer starts during the mixing process; a primary agglomerate is formed, the composition of which is dependent upon the structure. The important carbon black properties are surface area, specific activity, structure (void, volume, anisometry), and porosity of the particles. On heat treatment of black at 3000°C., it loses its sites of high specific activity. Structure and specific activity determine incorporation time and further dispersion. During mixing, bound rubber is formed which is used as a measure of specific surface activity. In the final vulcanizate, the filler–polymer interaction is evident in reduced swelling in solvents (benzene, chloroform, cyclohexane,) etc. Below a certain critical degree of swelling, the percentage swelling is no longer dependent upon the amount of filler in the vulcanizate. Graphitized black vulcanizates exhibit in all solvents the same degree of swelling as the unfilled vulcanizate. This phenomenon is explained by the assumption of mobile adsorption of rubber chains on the carbon black surface. In untreated blacks the mobility on the surface is limited by sites of high energy of adsorption. In graphitized blacks such sites are no longer found, and swelling is unhindered by the presence of black. Reinforcement is explained by the more homegeneous distribution of tension between molecular chains due to slippage on the carbon surface.

Mixing of carbon black and polymer: Interaction and reinforcement†‡

Stress relaxation in rubber stocks containing various fillers was measured at room temperature, and an empirical equation found for relating decrease in tension, ft, over a period of time from 0.1 sec. to 6 months, namely: 






where f1.0 is force after 1 min. of relaxation, n is the relaxation rate of material (by definition) and t is time in minutes. Raw rubbers were examined under compression, and cured rubbers were tested under tension. In both cured and raw butadiene rubbers, stress relaxation was found to be a viscous-controlled process. In raw rubbers, reinforcing carbon blacks decrease the rate of relaxation, while in cured rubbers the effect of carbon black is very small. However, in swollen (to VR = 0.25), cured rubbers, the rate of relaxation increases with increasing carbon black loading, indicating a slippage and/or breakage of some carbon black-polymer attachments.

Stress relaxation in rubbers containing reinforced fillers

The anomalous freezing point depression, ΔT, of benzene-swollen vulcanizates has previously been attributed to the limitation of (benzene) crystallite size by the polymer network. This study was initiated to determine the benzene crystallite size in a number of rubber and benzene systems. A special low-temperature specimen holder was designed and constructed in the Cambridge Laboratories for running diffraction patterns at temperatures near −30°C. X-ray line broadening techniques were used to study a series of filled and unfilled vulcanizates of varying crosslink density. The results indicate that crystallite size is not depressed to the degree predicted by freezing-point measurements. Benzene crystallite sizes were similar in all rubber benzene systems, regardless of degree of crosslinking or benzene fraction, although carbon black loading appears to increase crystallite size. This effect may be attributed to lesser depth of penetration of the x-rays due to greater density as carbon black loading increases. Additional studies measuring the ΔT for solutions and similar vulcanizates of NR and SBR over a wide range of rubber concentrations showed that at the same rubber in benzene fraction, crosslinking increases ΔT but the addition of carbon black reduces ΔT. An explanation for the observed phenomena is advanced.

Anomalous freezing point depression of swollen gels

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Carbon black–polymer interaction: A measure of reinforcement

Mixing of carbon black and polymer: Interaction and reinforcement†‡

Stress relaxation in rubbers containing reinforced fillers

Anomalous freezing point depression of swollen gels