摘要:

AbstractSample size sensitivity of thermal gravimetric analysis (TGA) presents a serious handicap in the obtaining of reliable thermal stability data for high‐temperature applications. For example, predictions of the apparent time for degradation during an isothermal experiment based on the results obtained using a 10 μm thick specimen can be off by an order of magnitude when applied to a product with a thickness of 10 cm. To address this effect, TGA experiments studying the thermal degradation of poly(methyl methacrylate) were conducted. Analysis of the experimental data resulted in the development of a relationship between the apparent time scale of the thermal degradation and the specimen thickness. Origins of the new dependence were traced to the change of the diffusivity resulting from material volatilization. Implications of the coupling between these two events for the analysis of thermal stability for new polymeric materials are discussed, and required changes in the current methodology are outlin

ISSN:0032-3888    

DOI:10.1002/pen.760330602

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe mutual diffusion coefficients for styrene‐butadiene rubber(SBR)‐n‐nonane systems were measured using a sorption apparatus with a quartz spring at 100 and 130°C for mass fractions of n‐nonane ranging from 0 to 0.16. The mutual diffusion coefficients were correlated with good agreement by the free‐vol

ISSN:0032-3888    

DOI:10.1002/pen.760330603

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe application of a method to determine and correct for the influence of non‐specimen extension in tensile testing is reviewed and demonstrated using two different thermotropic liquid crystalline polymers. In the tensile testing of high modulus polymer extrudate, where the amount of specimen extension is inferred from the crosshead travel, the error associated with system compliance can be significant and parameters such as modulus and elongation will be in error. The need to apply the correction depends on the magnitude of the product of the sample modulus and cross‐sectional area, divided by the test gage length, relative to the system compliance value. Its application is not necessarily restricted to high modulus materials, and can be extended to samples of larger cross‐sectional area and lower modulus. Guidance to assist in the choice of a suitable gage length to avoid compliance correction and a method to quantify the error contribution is pres

ISSN:0032-3888    

DOI:10.1002/pen.760330604

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThis work deals with the conductivity of polymer/filler‐mixtures, with the conductive filler particles of colloid size. For the interpretation of the conductivity course in such systems Wessling recently proposed a new thermodynamical percolation model, the so‐called “dynamic boundary model.” A consequence of the dynamic boundary model is a fixed picture for some properties of the mixtures, i.e., the density should vary in a defined manner according to the theoretical assumptions of the model. The current paper first gives a short description of the percolation process according to the dynamic boundary model. Second, the derivation of the density/filler concentration curves according to the assumption of this model is given. Third, a comparison is made between calculated and experimentally determined density/filler concentration curves. It is shown that the dynamic boundary model cannot account for the experimentally observed density

ISSN:0032-3888    

DOI:10.1002/pen.760330605

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of corona treating the surfaces of components on tensile properties of wood fiber linear low‐density polyethylene composites has been investigated. Corona treatment results in a significant increase in strength properties of the composites. Yield stress increases after treatment of one or both of the composite components. Pronounced improvement in ductility has been observed for composites containing 15 to 30% of the corona modified fiber. Relevant mechanisms involved are discusse

ISSN:0032-3888    

DOI:10.1002/pen.760330606

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe results of a round‐robin testing on the dynamic mechanical properties of a poly(ε‐caprolactam)/polypropylene PA‐6/PP compatibilized blend (an alloy) are reported. The alloy was a commercial product (Orgalloy R‐6000, from Atochem). The samples were prepared by extrusion, injection or compression molding. The greatest difficulty in comparing the data arose from the moisture content since the position of the PA‐6 transition peaks depend on the drying conditions. For the extruded specimens only minor effects could be attributed to the anisotropy introduced by the extrusion process. Overall, there was good agreement between the contributing laboratories for the frequency dependence of the transition peaks, but agreement between the measured values of the storage moduli was poor. This discrepancy is suspected to be partially due to the differences in sample geometry and in the processing

ISSN:0032-3888    

DOI:10.1002/pen.760330607

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractNuclear magnetic relaxation techniques have been used to study the microphase structure of sodium sulfonated polystyrene ionomers. Microphase separation in the ionomers could be evidenced by the magnetization decays, which were resolved into two components. At lower temperature, 300K, the decay function for the ionomer was found to be a combination of two Gaussian functions that are indicative of more rapid dephasing of individual spins, while the magnetization decay at higher temperature, 413K, was composed of both a Gaussian function and a Lorentzian function. The relative portion of the ionic phase in the ionomer was seen to be significantly affected by the ion concentration or the temperature. From the comparison of the relative amounts of the ionic phases obtained from both the material's composition and the nuclear magnetic relaxation experiment, it is anticipated that the ionic domains contain a substantial amount of hydrocarbon segments.

ISSN:0032-3888    

DOI:10.1002/pen.760330608

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe adverse effect of knit‐line formation on the mechanical properties of thermoplastics has been well documented for unfilled materials. A majority of these investigations concern amorphous polymers, whereas a number of engineering polymers are semicrystalline and also contain reinforcing fillers and fibers. The present investigation deals with the effect of knit‐lines on the mechanical behavior of unfilled and glass fiber‐reinforced semicrystalline polymers, such as polypropylene, poly(butylene terephthalate), poly(ethylene terephthalate), and poly(phenylene sulfide). Unfilled and fiber‐reinforced polystyrene was also investigated for reference. Tensile specimens with knit‐lines were produced by impinging melt fronts from two gates located at opposite ends of the dumbbell‐shaped mold. The effect of process conditions on the knit‐line strength was studied by varying primarily the melt and mold temperatures. The presence of glass fibers significantly reduced the knit‐line factor based on strength and strain to failure for the reinforced grades of all polymers relative to their respective unfilled grades. This is attributed to the lack of fiber flow across the knit‐line, which makes the material in the knit‐line region act as if it is not reinforced. The knit‐line strength could be changed through process modifications. For the unfilled grades of semicrystalline polymers, the presence of knit‐lines did not affect the yield strength but reduced the elongation at onset of necking, indicating that little spherulitic growth takes pla

ISSN:0032-3888    

DOI:10.1002/pen.760330609

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe dynamic operation of an ideal continuous‐flow stirred tank slurry reactor for propylene polymerization has been studied. A simple model is developed, which could be used for optimal computer control using advanced strategies. Step increases in input feed rates of propylene, solvent, and catalyst are used as the stimuli or forcing functions. It is assumed that the volume of the slurry in the reactor is maintained constant during the period. Responses of three output variables are studied, namely, monomer concentration in the liquid, volume‐fraction of solids in the exiting slurry, and average mass fraction of catalyst in the exiting macroparticles. It is found that the transients last for about five times the mean residence time of the reactor. Competing effects of changes in the diffusional resistance, number density of catalyst particles, and washout and dilution effects lead to interesting dynamic resu

ISSN:0032-3888    

DOI:10.1002/pen.760330610

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760330601

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY