ISSN:0032-3888    

DOI:10.1002/pen.760351902

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe objective of this study is to establish a feasible method for generating pressure‐specific volume‐temperature (PVT) data for thermoplastics on a microcomputer‐controlled injectionmolding machine (IMM). This method utilizes the injection barreel of the IMM as a pressure chamber for determining the specific volume of thermopla;stics at various pressure and temperature conditoins. An empirical equation of state based on the Tait equation s used to fit the PVT data of three resins — low‐density polythelene (LDPE), polystyrene (PS), and acrylonitrile‐butadiene‐styrene copolymer (ABS). The comparsion between LPDE's PVT data generating from the IMM and from the classical bellows method indicated that the present method can be reasonably applied for determining the specific volume of thermoplastics as a function of presure an

ISSN:0032-3888    

DOI:10.1002/pen.760351903

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper examines, through holding pressure, packing time, melt temperature, mold temperature and distance from the gate, the effect of molding conditins on the shrinkage of polypropylene and 40% calcium carbonate (CaCO3) filled polypropylene. The shrinkage longitudinal and transvrse to the flow direction were determined using a 127 × 76 × 4 mm thick plaque with a film gate. Marks were made ont he mold cavity to measure shrinkage at various distances from the gate. The results show that holding pressure and packing time are the most significant parameters. Cooling runners, however, could significantly influence local shrinkage values. Calcium carbonate reduces the shrinkage anisotropy as well as the cycle time of the molded parts. Shrinkage models have been developed using dual kriging statistical interpolation techniques and show an excellent fit with experimetnal dat

ISSN:0032-3888    

DOI:10.1002/pen.760351904

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA theoretical model is proposed for curing thermosetting polymers. The following heat transfer mechanisms are taken into account: convection through the heated fluid‐mold interface, conduction through the resin, and heat generated by chemical reaction. To study the influence of the convective heat in the curing step of the polymers, different external heating fluids are considered. Several chemical systems are used in the simulation. The results show that an apoxy requires precise control of thermal runaway. Criteria for processability are established and they provide a cycle time without promoting a damaging exother

ISSN:0032-3888    

DOI:10.1002/pen.760351905

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractMeasures of mixing for laminar flow are developed from basic principles of continuum mechanics for infinitesimal rates of stretch. The entire analysis is performed from the basis of the eigenvalues and principal directions of the appropriate flow tensors. Measuring the rate of line growth, where the line marks the interface between two miscible fluids, in terms of the major eigenvalue provides a direct measure of the maximum rate of mixing. Two efficiency measures for mixing are derived in terms of the eigenvalues and their directions. The creation efficiency of the magnitude of the major eigenvalue as a function of the energy input into the flow field is evaluated. The orientation of the interface to the principal direction qualifies the mixing efficiency in laminar flow. The new theory is used to analyze two‐dimensional and three‐dimensional channels. The results demonstrate not only the continuum measures for mixing but also extend our present understanding on mixing and provide future directi

ISSN:0032-3888    

DOI:10.1002/pen.760351906

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe melt flows of linear low‐density polyethylene (LLDPE) and branched low‐density polyethylene (LDPE) have been compared in a fully intermeshing co‐rotating twin‐screw extruder. The polyethylene melts were selected in order to investigate the effects of the melt rheology on the mixing. Their shear vicosity curves are quite similar, but the LDPE has a markedly higher apparent extensional viscosity over a wide range of stretch rates. The stagger of the paddles in the mixing zone of the extruder creates axial pressure‐driven axial flow can have significant extensional strain components. Residence time distributions obtained in the melt zones of the extruder with tracer dye reveal that the LDPE has a narrower residence time distribution than the LLDPE over a wide range of operating conditions. The axial dispersion for the LDPE is significantly lower than the axial dispersion for the LLDPE. This is attributed to the greater extensional viscosity of the LDPE. During the reactive extrusion process, solid maleic anhydride and polyethylene were added at the feed port but the peroxide provides better control of the crosslinking reaction. Residence time distributions measured for the chemically more reactive LLDPE melt indicate reduced levels of axial mixing with reaction. The reduction in mixing is due to a crosslinking reaction that occurs in parallel to the grafting reaction. This change in mixing is smaller than the difference in mixing between LDPE

ISSN:0032-3888    

DOI:10.1002/pen.760351907

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe simulation of the parison formation process in blow molding has been studied. The flow field was divided into two regions, namely, the extrudate swell region near the die lip and the parison formation region after the exit swell. In the swell region, we predicted the swelling ratio and residual stress distribution for high Weissenberg numbers for steady planar well using the 1‐mode Giesekus model. In the parison formation region, the flow is assumed to be an unsteady unaxial elongational flow including drawdown and recoverable swell and is modeled using the 10‐mode Giesekus model. We calculated the time course of parison length and thickness distribution, and compare the calculation results of parison length with experimental data. It was found that the predicted values agreed rather well with the experimental values. The calculation results could especially predict the shrink‐back, which is the phenomenon where the parison length becomes shorter after the cessation of extrusion, and it was found tat this was caused by the recoverable swell of the parison, which depends on the tensile stress generation in the die. Various flow rates and die geometries were studied and confirmed the reliability and usefulness of the m

ISSN:0032-3888    

DOI:10.1002/pen.760351908

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of drawing temperature on multi‐stage drawn ultra‐high molecular weight polyethylene (UHMWE) fiber, produced by gel spinning, has been studied. Drawing at higher temperature generally gives higher crystal orientation, as expected. The activation energy of drawing increased with the draw ratio and raw 4sequence. It varied at a given draw ratio and draw stage between two temperature ranges, 85 to 115°C and 115 to 135°C. Thus, for the first draw stage, the activation energy is ∼ 19—35 KJ/Moe in the range of 85 to 115°C, and ∼ 60—99 KJ/mole in the range of 115 to 135°C. In the second stage, the activation energy is 40 KJ/mole in the range of 105 to 115°C and 70—99 KJ/mole in the range of 115 to 135°C. In the third stage, the activation energy is ∼ 92—100 KJ/mole in th

ISSN:0032-3888    

DOI:10.1002/pen.760351909

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe uniformity of films and their surface roughness are of great importance in applications involving information recording (videotapes etc.). These properties of polymers processed with such film production techniques as tenter frame operations are not well understood. To understand the relationships between the process variables, such as stretching mode, rate of stretching, temperature of stretching, and material characteristics, melt cast amorphous PEEK films were subjected to systematic experiments involving variations of the process parameters. The results reveal that stress hardening in the stress strain curves plays an important role in defining the level of thickness uniformity and surface roughness. It the films are stretched in a way that they do not experience stress hardening, the resulting films were found to have significant variations in thickness, sometimes worse than those of precursor materials. In all cases, where films are subjected to substantial stress hardening, the above two parameters improved dramatically. This indicates that no matter what the stress response of the film, those films stretched to intermediate stretch ratios have poor thickness uniformity and surface quality. Once the stress hardening takes effect, the deterioration of the dimensional parameters was found to stop and reverse and ultimately reacha point in deformation space where the film quality was better than that of the original films. This is solely attributed to the stress hardening that allows the thinned sections of the films to sustain higher loads, thereby propagating the deformation to other underformed areas in the films, which in turn causes a “self‐leveling” effect. An important implication of this finding is that to obtain films of optimum thickness and surface quality, they need to be stretched beyond the (global) stress hardening point. Otherwise, less than desirable film quality may r

ISSN:0032-3888    

DOI:10.1002/pen.760351910

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe self‐wiping co‐rotating twin‐screw extruder was studied as a reactor for two polymerizations in bulk: the homopolymerization of n‐butylmethacrylate and the copolymerization of n‐butylmethacrylate with 2‐hydroxypropylmethacrylate. The influence of the extrusion parameters on the product was analyzed. With both reactions, conversions up to 95% were obtained. Nevertheless, a significant difference was observed in the working domain of both polymerizations, in which a stable reactive extrusion process could be attained wherein the discharge rate is constant and equals the feed rate. In the case of the relatively fast copolymerization, both the throughput and the screw rotation rate could be raised without endangering the stability of the process. This was not the case for the homopolymerization studied. It was determined that the stability of the process depends on the reaction velocity and the product viscosity. Within the boundaries of the working domain, the molecular weight could be influenced by adjustments of the extrusion

ISSN:0032-3888    

DOI:10.1002/pen.760351911

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY