摘要:

AbstractThe effect of processing variables on the knit line structure of nylon 6 samples was investigated. Either local sample thickening or grooves were observed at the knit lines for samples injected with mold conditioning temperatures of 130° and 30°C respectively. The results also indicate that shrinkage venting, either to or from the weld zone, is the dominant mechanism for knit line formation, which is thus related to the position where complete cross section solidification first takes plac

ISSN:0032-3888    

DOI:10.1002/pen.760290402

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractShear modification treatment represents a special shearing history affecting mainly the elastic behavior of polymer melts. This process has been attributed to reversible physical changes in the entanglement structure of the polymer chain network. Shear modification studies were performed for two well‐characterized low‐density polyethylene (LDPE) grades differing in molecular weight distribution and degree of long chain branching. The shear working of the material was carried out using a specially designed shearing unit producing definable amounts of pure shear in a continuous process. Measurements of the dynamic storage modulus,G′, steady‐state shear compliance;Je, extrudate swell, melt flow index, and the extensional behavior (Rheotens test) indicate that primarily properties associated with the elasticity of the melt are reduced in value. The observed reduction is found to correlate with the mean specific energy dissipated during sample preparation. Comparing the two LDPE grades showed that higher degrees of modification can be obtained at lower energy input levels for the more highly branched grade. Reversibility tests were performed and complete recovery of the initial material behavior was observed. Comparison of measurement results for samples prepared using the shearing unit presented here and a Brabender Plasticorder indicates that the degree of modification depends not only on the molecular structure of the polymer but also on the manner in which the shearing history is imposed upon the m

ISSN:0032-3888    

DOI:10.1002/pen.760290403

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThree styrene‐butadiene‐styrene (SBS) block copolymers were cast into sheet form, and the resulting microphase‐separated specimens were tested in tensile free recovery. After an initial strain of 300%, specimens were released and their lengths measured for about a week. For one polymer, the recovery curves are presented for seven temperatures in the range −40 to +80°C; other data are given at 22°C. Analysis of the recovery curves, using as the model a series assembly of Kelvin elements, obtains time constants for microstructural repair and explains the temperature dependence in terms of the microstructural interphase and its partial vitrification. Differences among the three polymers can be interpreted by recognition of styrene‐block molecular weights, as well as by the volume fractions of the domain styrene cores and interphases. Additional structural information arises from torsion pendulum experiments over −120 to 100°C for unstretched, stretched (300%), and partially rec

ISSN:0032-3888    

DOI:10.1002/pen.760290404

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe same three styrene‐butadiene‐styrene copolymers discussed in the companion paper (this issue) were tested by cycling in uniaxial tension/retraction, with large magnitude (to 600% in some cases) and different sequences and rates. The behavior of “set”, at the end of each retraction, is examined in detail and invoked to explain several other features of the stress‐strain curves. Time scales for structural recovery determined in the companion paper are found to assist this interpretation. Quantitative modeling of the isostructure retraction curves is accomplished in terms of the Mooney‐Rivlin strain function, modified to employ a strain variable amplified by the volume of broken glassy “filler”. Values of the two Mooney moduliG1andG2are used to infer various features of the

ISSN:0032-3888    

DOI:10.1002/pen.760290405

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractBlends of polycarbonate (PC) and poly(ethylene terephthalate‐co‐p‐oxybenzoate) (PET/PHB60) were prepared by melt‐blending. Physical and/or chemical interactions between the two phases of the system were studied by thermal analysis and infrared spectroscopy. Rheological measurements in shear flow were carried out both in the low and high shear rate regions in the temperature range of the existence of the mesophase. At low liquid crystalline polymer (LCP) content, the blends showed flow curves similar to those of the unfilled PC, while at higher LCP percentages the rheological behavior of the pure LCP was resembled. Moreover, in the whole shear range, the viscosity values of such blends were in between those of the pure polymers. The influence of the addition of 10% LCP on the mechanical properties of the PC was investigated. Fiber‐spinning was performed under different experimental conditions, and it was found that opportune drawing conditions are necessary to improve the modulus of the matrix. Morphological analyses of the pure LCP and of the blends were related to the rheological and mechanical behavior of these systems. While the LCP exhibited an elevated dimensional stability, the inclusion of the LCP in PC matrix did not improve the dimensional stability of t

ISSN:0032-3888    

DOI:10.1002/pen.760290406

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractFlow visualization experiments of polycarbonate and polystyrene resin extrusion were performed to observe the melting mechanism and the flow kinematics around the solid‐bed in the melting zone of a single screw extruder. The axial solids content and pressure profile calculations of the Tadmor melting model were modified as a result of variable solid‐bed velocity and solid‐bed temperature observa

ISSN:0032-3888    

DOI:10.1002/pen.760290407

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe problem of inhomogeneous swelling of polymers around particles or fibers is treated analytically within the context of Gaussian statistics for polymer chains and the Flory‐Huggins approximation for the interaction between polymer and solvent. The resulting differential equation for the displacement field around the inclusions is quite simple; it contains a homogeneous part and a nonlinear part. The nonlinear part of the differential equation is preceded by a parametern(1 − 2χ), wherenis the molecular weight between crosslinks and χ is the Flory‐Huggins interaction parameter. Accordingly, the displacement field for the case of theta solvent, i.e. χ equals 0.5, can be solved exactly. In good solvents, the problem can be treated as a perturbation of the theta solvent condition. The amount of deviation from the theta solvent solution is obtained through a numerical technique and the results are tabulated as a function ofn

ISSN:0032-3888    

DOI:10.1002/pen.760290408

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760290409

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760290401

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY