摘要:

AbstractExtrudate swell studies of a high‐density polyethylene (HDPE) melt have been undertaken in flows through slit and capillary dies with the purpose of finding out the effect of die‐length/diameter (gap) (L/D or L/2H) ratio on the viscoelastic behavior. Numerical solutions have been obtained by using the finite element method (FEM) and an integral constitutive equation of the K‐BKZ type with a spectrum of relaxation times. The material parameters have been obtained by fitting experimental viscosity and normal stress data for the melt as measured in shear, and elongational viscosity data available in the literature. Different L/D (L/2H) ratios have been considered ranging from very short to infinitely long dies. The numerical simulations reveal that as the flow rate increases, viscoelastic effects exhibited by the HDPE melt become important and manifest themselves in an enhanced swelling behavior after the die exit, while small, Newtonian‐like vortices exist in the contraction before entry to the die. Elastic recovery is also captured in an enhanced extrudate swell, which is always higher at the same apparent shear rate for the capillary than the slit dies and decreases drastically as the L/D (L/2H) ratio increases, reaching asymptotic values for very long dies. Such behavior is in agreement with experimental findings from flows through slit and capillary dies and in sharp contrast with purely viscous simulations which cannot predict such strong viscoelastic phenomena associated with the memory of the polymer melt. © 1993 John Wiley&S

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe orientation characteristics of extruded poly(ethylene terephthalate) (homopolymer) sheets are discussed with respect to: mode of extension (simultaneous versus sequential), strain rate, stretch ratio, and temperature. The nature of the stress–strain curve recorded during the process of extension, and its dependence on the parameters of extension mentioned above, are analyzed. Results show that for specimens stretched in the biaxial simultaneous mode, the stress–strain curve is concave upward, which is typical for amorphous polymeric materials. Strain‐hardening occurs at high planar extensions, and is accompanied by a steep rise in the stress measured during stretching. The magnitude of this stress increases with increasing strain rate and extension ratios, but decreases with increasing temperature of stretching. During biaxial sequential extension, the stress–strain curve is concave upward at low strain rates or at high temperatures of stretching, but becomes convex upward at higher strain rates or lower temperatures. The curve also changes from concave to convex upward at high limiting extension ratios in the first direction. The convex upward nature of the stress‐strain curve is typical of semi‐crystalline materials, indicating the occurrence of strain‐induced crystallization during stretching in the first direction. Again, the level of stress, measured during stretching, increases with increasing strain rate and limiting extension ratio in the first direction, while it decreases with increasing temperature of stretching. © 1993 John W

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractResults of a study of the orientation characteristics of extruded poly(ethylene terephthalate) (PET) (Homopolymer) sheets are discussed with respect to stretching condition. PET exhibits strain‐induced crystallization upon being stretched to large extension ratios. This may lead to strain‐hardening, which is accompanied by an upswing in the stress–strain curve recorded during the process of extension. A parameter pertaining to the extension ratio, at which the onset of strain‐hardening occurs during stretching of the specimen, is defined. This is called the strain‐hardening parameter (SHP). The dependence of the SHP on the mode of stretching, the temperature of stretching, the strain rate, and the limiting extension ratio in the first stretch direction, are studied. It is seen that the SHP in both simultaneous and sequential modes decreases with increasing strain rate and the limiting extension ratio in the first stretch direction, while it increases with increasing temperature of stretching. For specimens stretched in the simultaneous mode at 90°C, SHP versus extension rate shows a minimum. This could be due to viscous dissipation at high rates of extension. Also studied is the relationship of strain‐hardening and the SHP with strain‐induced crystallization. It is seen that for specimens stretched in the uniaxial constrained mode, the rapid increase in properties with extension occurs much before the upswing in the stress–strain curve. The upswing occurs at the extension ratio at which the increase in properties once again becomes gradual. This means that the upswing in the stress–strain curve indicates significant completion of strain‐induced crystallization and the establishment of structural order within the specimen. © 1993

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractCommercial operations for producing Poly(ethylene Terephthalate) (PET), Blow molded oriented containers and films, usually involve stretching PET either in simultaneous or sequential modes. The specific orientation characteristics of these two modes are studied with respect to the stress‐strain curves and the strain‐hardening parameter. Degree of orientation, crystallinity, and physical properties are studied for each mode as functions of stretch ratio and temperature. The relationships among physical properties, orientation, and below molding characteristics are studies. © 1993 John Wiley&Sons,

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe influence of solid‐state modified polypropylene on the physical performance of uncoated or thermoset‐resin coated sawdust‐filled polypropylene composites was studied. The effect of composition of the composites on tensile strength, Young's modulus, tensile toughness, elongation, and impact strength was determined through two 23factorial rotatable designs. The results of this investigation show that both the m‐phenylene dismaleimide‐modified polypropylene precompounded sawdust as well as solid‐state modified maleated polypropylene can be successfully used to prepare sawdust‐filled polypropylene composites with good tensile strength. On the whole, this property improved compared to that of unfilled polypropylene. According to the analysis of factorial design, the optimum composition to prepare a composite with highest tensile strength within the experimental range was 30–40 wt% phenolic resin coated sawdust together with 4–6wt% solid‐state modified maleated polypropylene; while the product composition for the worst design was a combination of high amount of phenolic resin modified polypropylene with phenolic resin coated sawdust. The experimental design also concluded that effect of compositions on impact strength of composites was not significant in most of the cases. Overall, the empirical models constructed in this study provided a good approximation to actual experimental measurements; we are encouraged to extend this approach to processing conditions for manufacturing these composites. © 1993

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractRecovery of value from cured unsaturated polyesters, other than the approach of grinding the resin and blending it with virgin resin for applications of minor importance, has been difficult. The long established position of the resins in the marketplace, their complex composition, and economic considerations have been major obstacles. This article reports results obtained on recovery of soluble, well‐characterized products from cured resins by neutral hydrolysis and on some experimental applications of the products. © 1993 by John Wiley&Sons, I

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAn overview is presented of the currently studied microwave‐assisted chemical and physical processes, as they pertain to polymers. Furthermore, the features which affect the microwave heating of polymers are described. Finally, some of the factors which have limited more widespread acceptance of microwave processing of polymeric materials are highlighted. © 1993 by John Wiley&Sons, I

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY