摘要:

Mineral sulfur is a widely used ingredient to form cross-links between the rubber chains in the vulcanization process. During compounding, a high elastic state of sulfur at temperatures between 40°C and 70°C promotes elongation of its particles and, next, breaking these thin and weak needles into pieces. This increases the surface area of particles and, after melting, creates conditions for intensive diffusion of sulfur into the rubber matrix, which helps to equalize the distribution of sulfur in cured rubber. Sulfur is relatively uniformly distributed in the bulk of rubber compound. However, during storage of rubber compounds, a thin layer of sulfur is observed on their surface (a bloom). This detrimentally affects processing and has an influence on cured rubber properties in use. Up to 40°C, the concentration of bloomed sulfur increases as the storage time of a rubber compound is prolonged. For temperatures above 42°C, bloomed sulfur disappears gradually. The eutectic alloy of sulfur/stearic acid should play an important role in the disappearance of a bloom layer from the surface of a rubber compound stored at a temperature above 42°C. This is because the melting point for this eutectic, about 46°C, is very close to that at which the change in mechanism of blooming was noticed. Under this condition, sulfur, as a eutectic, is in a molten state; due to this, it can diffuse into the polymer matrix. Formation of a eutectic is possible if molten particles of the curing system, containing sulfur, accelerator(s), stearic acid, and zinc oxide, will meet each other inside the rubber matrix during the last stage of compounding.

ISSN:0022-2348    

DOI:10.1080/00222349808220461

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The influence of the chemical composition on the phase structure, and from this the structure-property relationships, of poly[ester-block-ether] (PEE) elastomers based on poly(butylene terephthalate) (PBT) hard segments and oligo(α,ω-dihydroxy poly(oxytetraniethylene)) (PTMO) and/or dimer fatty acid (DFA) soft segments was investigated using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile testing. Differences in thermal and mechanical properties with varying hard and soft segment composition are interpreted in terms of the phase miscibility of the various polymers studied.

ISSN:0022-2348    

DOI:10.1080/00222349808220462

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The mechanical and rheological properties and porosity of polymer blends of thermoplastic elastomers (styrene-butadiene-styrene, SBS) with polystyrene used as a matrix for composites filled with rubber scrap were investigated. The influence of the rubber scrap content (from 45 to 67 wt%), as well as the content of thermoplastic elastomer (SBS), polystyrene, and oil on the mechanical and rheological properties and porosity of blends are discussed. The processing properties of blends are expressed through the values of melt viscosity, shear rate, and indexnfrom the power law. The porosity of the blends after extrusion at a temperature of 160°C was estimated.

ISSN:0022-2348    

DOI:10.1080/00222349808220463

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The propagation of ultrasound waves in thermoplastic multiblock elastomers was investigated by measurements of the ultrasound velocity and attenuation. Three polymer series with amorphous-crystalline structure were studied. The soft-segment material was composed of three different oligomers for the three series: poly(1,4-oxypropylene)diol for series A, oligo(oxyethylene)diol for series B, and dimerized fatty acid for series C. The hard-segment material was composed of poly(butylene terephthalate) (PBT). The ultrasound velocity and attenuation of these elastomers with variable hard-segment concentration were investigated as a function of the temperature. The observed relaxation processes were ascribed to the glass transition of the soft phase. The possibility of a general description of these systems is discussed.

ISSN:0022-2348    

DOI:10.1080/00222349808220464

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The mechanical and Theological properties of blends based on commercial types of thermoplastic elastomers (TPEs) Finaprene with polystyrene and ethylene-vinylacetate copolymer, used as suitable materials to produce highly filled composites with magnetically hard fillers, have been investigated. The influence of a 90% to 93% filler content and the morphology of the fillers on mechanical, Theological, and magnetic properties of composites is discussed. The influence of changes of other technological parameters, such as type of treatment of the fillers and type of mixer, on properties of composites has been studied.

ISSN:0022-2348    

DOI:10.1080/00222349808220465

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Shear flow of microphase-separated melts of symmetric diblock copolymers is simulated by the cooperative motion algorithm. Morphologies in stationary states under various shear stresses and after cessation of flow are analyzed. Considerable effects of copolymer interaction with walls on morphologies under flow are detected.

ISSN:0022-2348    

DOI:10.1080/00222349808220466

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The thermal expansion behavior of different types of rubber-toughened poly(methyl methacrylate) (PMMA) composites was determined over a wide range of temperatures and different filler-volume fractions. In a previous publication, the thermal expansion coefficients of particle-reinforced polymers were predicted by means of a theoretical model especially developed that takes into account the adhesion efficiency between the inclusions and the matrix material through the concept of the boundary interphase, that is, a layer between the matrix and the fillers that has a structure and properties different from those of the constituent phases. This layer was assumed to have varying properties. Predictions of the model were in good agreement with experimental results. In the present work, the same model was used in order to study the effect of interphase thickness on the thermal expansion behavior of onion-structure, rubber-modified, paniculate PMMA materials. It was found that the interphase volume-fractionViof these materials changes dramatically with the filler-volume fractionVf. More precisely, at lowVfvalues,Viincreases, withVfshowing a maximum at a specificVfvalue; at higherVfvalues, it decreases. This kind of behavior was also previously observed in the case of metal-particle-reinforced resins and other types of particulates, but its explanation has been obscure until now.

ISSN:0022-2348    

DOI:10.1080/00222349808220467

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The number of phases, transition temperatures, and microhardness of a series of poly(ester ether carbonate) (PEEC) multiblock terpolymers with poly(butylene terephthalate) (PBT) hard segments have been investigated as a function of ether/carbonate (EC) soft-segment composition at constant PBT content. The polymerization degree of PBT and the intrinsic viscosity of the terpolymers were determined by viscosimetry. The degree of crystal-Unity, long spacing, glass transitionsTg, and melting temperature were derived by means of x-ray diffraction, dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC) measurements. Surface mechanical properties were studied by microindentation tests. It was found that the terpolymer consists of two amorphous (EC and PBT) phases and one crystalline (PBT) phase. TheTgvalue of PBT does not depend on the chemical composition of the soft segments, in the contrast to theTgof the soft-segment amorphous phase. Introduction of polycarbonate moities in the soft segments induces an increase ofTgby 50°C without formation of an additional (third) amorphous phase. The reduced crystallizability of PBT hard segments (by a factor of 3) is explained by this decrease of flexibility of the soft segments, which also causes a twofold reduction in the microhardness values. The dominating contribution of crystallinity to the microhardness is shown. However, the much lower measured overall microhardness in contrast to the one calculated by means of the additive law is explained by the plasticizing effect of the soft amorphous phase. This assumption is in agreement with the structure model derived from the small-angle x-ray (SAXS) and wide-angle x-ray (WAXS) data.

ISSN:0022-2348    

DOI:10.1080/00222349808220468

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A hypothesis (theory) has been formulated for steric stabilization during simple shear flow of discrete domains of one polymer A in a continuous phase B by block copolymer addition. A limiting solution found when the molecular weights of the components are high predicts preformed small drops stabilized by block copolymers at the interfaces are stable below a critical shear stress τcrbut unstable above τcrInterfacial placement in well dispersed blends of PS/PMMA/PS-b-PMMA was deduced by interfacial tension measurement, structure development studies, and viscosityshear rate studies with and without block copolymers. The experimentally determined critical shear stresses show relatively poor reproducibility (SD ± 10%). For measurements at shear stresses larger than the critical values, interesting time effects are observed, whereas scattering signals are constant at shear rates lower than τcrThe hypothesis is not rejected when compared with experimental data from light-scattering measurements during flow.

ISSN:0022-2348    

DOI:10.1080/00222349808220469

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

New block terpolymers of the poly[oxytetramethylene-block-(tetramethylene terephthalate)-block-lauroIactam] (PTMO-b-PBT-b-PA12) with potential applications as elastomers have been obtained by melt polycondensation of dimethyl terephthalate (DMT), 1,4-butanediol (BD-1,4), poly(oxytetramethylene)diol (PTMO), and α,ω-dicarboxylic-oligolaurolactam (PA 12) in the presence of magnesium-titanate organometallic complex as a catalyst. The influence of changes in the degree of polycondensation of poly(tetramethylene terephthalate) (PBT) on the structure and thermal and mechanical properties of the terpolymers has been determined by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and other standard physical methods. The system is characterized by a mutually disturbing effect of PA 12 and PBT segments on the phase structure of the terpolymers. Intermolecular interaction between these segments influences the elastomeric properties of these poly[ether-block-ester-block-amide] terpolymers.

ISSN:0022-2348    

DOI:10.1080/00222349808220470

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor