摘要:

AbstractThe kinetics of isothermal crystallization of polymer blends in which the matrix is a crystallizable polymer is considered. It is shown that depending on the difference in interfacial energies the inclusions are rejected or engulfed by the growing spherulite. Other factors influencing rejection, engulfing, and/or deformation of dispersed particles of the second polymer are the viscosity of the melt, the spherulite growth rate, and the size of dispersed particles. If the difference in interfacial energies is positive, then rejection or engulfing requires additional work to be done by the crystallization front. This dissipation of energy decreases the spherulite growth rate. It is estimated that the rejection of the second component is the most important phenomenon in the crystallization of blends. The spherulite growth rate of isotactic polypropylene in blends with low‐density polyethylene and several elastomers was studied as a function of crystallization temperature and concentration. The comparison of growth rate data with morphological changes occuring during crystallization of blends studied shows very good agreement with the theoretical predictions based on energetics consideration

ISSN:0032-3888    

DOI:10.1002/pen.760241502

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760241503

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractWood pulp fibers possess strength and modulus properties which compare favorably with glass fibers when the differences in fiber densities are considered. Softwood pulp fibers with fiber aspect ratios near 100 are readily dispersed into high‐density polyethylene or isotactic polypropylene with the aid of carboxyic dispersing agents to form mixtures containing 50 weight‐percent wood pulp which can be readily injection molded. The mechanical properties of the molded specimens were similar for all types of pulp including Kraft (bleached and unbleached), mechanical and chemical‐mechanical pulps, waste pulps, and reclaim newspapers. Comparisons of the stiffness/weight efficiencies revealed that pulp composites equal or exceed the stiffness of most traditional materials of construction including steel, aluminum, glass‐fiber composites, and talefilled polyolefins, while retaining a major material cost advantage. The measured strength values of the pulp composites were less than the theoretically predicted values due to the presence of voids created by the formation of volatiles during processing. Mechanical pulps which were available in dry form were preferred because of lower cost and ease of handling. Wood fibers are non‐abrasive so that relatively large concentrations may be incorporated into polyolefins without causing serious machine wear during mixing and fa

ISSN:0032-3888    

DOI:10.1002/pen.760241504

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA simple test device is described for subjecting bars to large bending deformations and simultaneously monitoring the bending moment. Examples are given of the elastic bending of a bar of a natural rubber vulcanizate and of the maximum bending moment that molded bars of polyethylene and polypropylene can withstand before the fully‐plastic state is attaine

ISSN:0032-3888    

DOI:10.1002/pen.760241505

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractCritical strains causing environmental stress cracking of injection‐molded poly(acrylonitrile‐butadiene‐styrene) (ABS) and poly(styrene‐acrylonitrile) (SAN) plaques were determined upon exposure to methanol. Measurements were obtained for samples strained either parallel or perpendicular to the melt flow direction and for samples located at various distances from the mold gate. Critical strains were significantly higher in the direction parallel to the melt flow compared to the transverse direction. The degree of anisotropy increased with increasing rubber content. For ABS containing 46 percent rubber, the critical strain at one point was determined to be 2.99 percent in the direction of melt flow, but only 0.47 percent in the orthogonal direction. For this material, critical strains determined parallel to the melt flow decreased with distance from the gate; whereas, critical strains for SAN and ABS containing 30 percent rubber remained essentially constant. Orientation of the plaques was assessed using shrinkage determinations and a thermal conductivity technique. Though a straightforward correlation of orientation with critical strain is observed for ABS, a similar relationship is not observed for SAN. These results suggest that although stress cracking occurs in the glassy matrix of ABS, it is the dispersed rubbery phase which controls the magnitude of strain required to initiate c

ISSN:0032-3888    

DOI:10.1002/pen.760241506

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractTo predict the fatigue performance of talc‐filled polypropylene in engineering applications, a simple relationship using constant stress data to predict the cycles‐to‐failure (Nf) was developed:\documentclass{article}\pagestyle{empty}\begin{document}$$ N_f = kv\sigma ^{ - n} f(n) $$\end{document}wherekandnare constants from creep rupture tests,vis the cyclic frequency (≤1 Hz to avoid self‐heating),f(n) is a function that accounts for the wave form, and a is the peak cyclic stress with a zero minimum stress. For stress concentrations produced by central holes, σ is taken as the average net section stress and the effect of the stress concentration is ignored. Extensive tests were used to verify this expression for cyclic frequencies of 1.0 and 0.1 Hz, sinusoidal and triangular waveforms, stress concentrations produced by small and large holes, and 20 and 40 percent talc fill

ISSN:0032-3888    

DOI:10.1002/pen.760241507

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA basic study of the kinematics, dynamics, and heat transfer occuring during tubular film extrusion of polyethylene is outlined. Three rheologically characterized polyethylenes, a low‐density polyethylene (LDPE), a linear‐low‐density polyethylene (L‐LDPE), and a high‐density polyethylene (HDPE) were used in this study. The kinematics and stability of the tubular film process were investigated over a wide range of blow‐up ratios, drawdown ratios, and frost‐line heights. Local deformation rates along the bubble have been determined. Regions of stability and instability are described. Tensions and inflation pressures have been measured and expressed in terms of locol elongational viscosities. Temperature profiles along the bubble were determined and interpreted in terms of local heat transfer coefficients. Positions of crystallization and temperature profiles have been noted and used to estimate rates of crystallization. The characteristics of the LDPE, LLDPE, and HDPE a

ISSN:0032-3888    

DOI:10.1002/pen.760241508

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractIt has been observed in dynamic mechanical measures that the range of temperatures in which relaxation properties are affected by the diminishing of the free volume has, as a lower limit the temperature at which the maximum ofG″ ortgδ, corresponding to the β relaxation, occurs. In dielectric measures on polymers in which the β relaxation is not predominant over the α relaxation, this temperature range is scarcely affected by changes in frequency, whereas the peak shifts according to its activation energy. This fact leads to the conclusion that the decrease in free volume due to a slow cooling from a temperature aboveTgmainly affects mobility of the main chains underTg, without disturbing the groups that give rise to the secondary relaxa

ISSN:0032-3888    

DOI:10.1002/pen.760241509

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe polycondensation step of poly(ethylene terephthalate) (PET) formation is assumed to include various side reactions in addition to the usual polymerization reaction. Polymerization in the batch reactor at constant pressure has been modeled to flash volatile components at the end of small discrete time intervals with polymerization occurring during the interval. The Hamiltonian has been written for the time interval and optimum temperature history computed for batch reactors for various reactor pressures. For low pressures, computed optimum temperature history is found to be of similar nature as that used in industry.

ISSN:0032-3888    

DOI:10.1002/pen.760241510

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractLinear‐low‐density polyethylene (LLDPE) is steadily gaining importance in a wide variety of applications due to its excellent performance characteristics in the final product. The rheological properties of LLDPE in the dynamic and steady state are of great pragmatic importance and these have been studied in the present work. A correlation between the dynamic and steady‐state rheological properties has been attempted and good agreement has been

ISSN:0032-3888    

DOI:10.1002/pen.760241511

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY