摘要:

AbstractSurface of the carbon fibers developed from PAN (polyacrylonitrile) has been modified using such methods as air oxidation, nitric acid treatment, and anodic (electrolytic) oxidation. By choosing optimum treatment parameters, the tensile strength of such fibers has been found to increase by about 60 percent over that of the untreated value. A quantitative estimation of the surface groups formed during the treatment shows an increase in number with severity of the treatment. Further, removal of these functional groups from the fiber surface during degassing at 1000°C also influences the mechanical properties of the carbon fibers considerably. Results have been discussed in detail

ISSN:0032-3888    

DOI:10.1002/pen.760240702

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractDrying of hygroscopic plastics in preparation for molding or extrusion is characterized by very low moisture levels in the polymers and by very low humidity in the drying air. In these circumstances, diffusivity is essentially independent of moisture concentration but surface concentration will vary with time in the general case. An exponential surface concentration/time function is derived from fundamentals and applied to the solution of the diffusion equations for slabs and spheres. Under ideal drying conditions, the solutions reduce to the elementary case in whichcs=cffor θ>0. For non‐ideal drying, the exponential factor b̃ in the surface concentration function appears in the solutions of the diffusion equations. Experiments on slabs were used to verify the analysis since ideal or non‐ideal drying conditions could readily be set up with molded slab samples. Experimental drying curves are in agreement with theory. To complete the analysis for engineering applications, equations for counter flow heat transfer in the dryer hopper are derived and combined with the diffusion solutions to generate dryer performance

ISSN:0032-3888    

DOI:10.1002/pen.760240703

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThis paper shows that the tensile properties of high‐density stiff foams having cellular structures consisting of spherical voids can be described and predicted by simple rules. These rules are derived from other known and experimentally established relationships describing particulate systems of continuous glassy matrices containing a uniform dispersion of solid glass bead

ISSN:0032-3888    

DOI:10.1002/pen.760240704

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractAn experimental study was conducted on the injection molding of a thermosetting polyester resin. For the study, a general‐purpose unsaturated polyester resin was used, with benzoyl peroxide as initiator. A differential scanning calorimeter (DSC) was used for studying the curing kinetics, under isothermal curing conditions. A plunger‐type injection‐molding apparatus was constructed, and a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a film the changes in stress birefringence patterns in the mold cavity during the molding operation (i.e., during the isothermal cure, post cure, and subsequent cooling), using a crossed circular polariscope. The injection‐molded specimens were used to determine the distribution of the degree of cure at various positions in the flow direction, and to relate the degree of cure to the dynamic mechanical pro

ISSN:0032-3888    

DOI:10.1002/pen.760240705

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThis paper proposes a new solution for the problem of thermally developing flow in a single‐screw extruder with power law fluids. It is shown that a transformation to a Lagrangean frame enables one to extend the solution to extrusion situations where appreciable “pressure back flow” exists. The utility of the model is demonstrated using a polystyrene melt as a model

ISSN:0032-3888    

DOI:10.1002/pen.760240706

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe morphology of blends of high‐density polyethylene (PE) and isotactic polypropylene (PP) was studied by mesans of optical and scanning‐electron microscopy. In the range of 10 to 90 percent by weight PE, these blends are two‐phase systems, the components of which crystallize separately into discrete phases. The presence of PE has a definite and pronounced effect on the crystalline structure of the PP, whose spherulitic structure becomes increasingly irregular and coarse with increasing PE content. The light transmission of these blends during melting and crystallization was also studied in an attempt to characterize

ISSN:0032-3888    

DOI:10.1002/pen.760240707

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe durability of the joints, consisting of α‐Al2O3primed with γ‐aminopropyl triethoxysilane (γ‐APS) and polyethylene (PE), in wet environment is investigated as a function of the γ‐APS thickness, dehydration of γ‐APS prior to joint formation and redrying the joint after a certain exposure. The joint strength measured by 180°s peel is found to decrease with exposure time in wet environment more rapidly in water than in 100 percent RH. With exposure time, the debonded area increases from the edges toward the central area of the joint. Relatively thin γ‐APS treatments on α‐Al2O3appear to provide a more durable joint than thicker γ‐APS treatments resulting in an optimal thickness in the range of 0.3 ∼ 1 percent γ‐APS concentration level. Dehydration of γ‐APS leads to more durable joints with an optimal condition found between 1 ∼ 2 days of dehydration at 100°C in vacuum. Regardless of the γ‐APS thickness and dehydration history, the failure in the de‐bonded area seems to occur by the hydrolysis of γ‐APS near the α‐Al2O3side and by the deformation of polyethylene (cohesive failure) in the peeled area, as characterized by SEM and ESCA. The debonded area in the dried joint recovers little strength, but in the central bonded areas, the strength is mostly recovered, characterized by cohesive failure of polyethylene. Diffusion of water in γ‐APS near the α‐Al2O3side rather than the PE side can explain at least qualitatively most of the observed trends. The effects of γ‐APS thickness and dehydration on the durability in wet environments are compared with those on adhesion promotion in dry e

ISSN:0032-3888    

DOI:10.1002/pen.760240708

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe flow of polypropylene, nylon 6,6, and 33‐percent glass‐fiber‐filled nylon 6,6 into a tensile bar mold was investigated. Pressures needed to fill the cavity and runner system were measured as a function of fill time and melt temperature. The experimental results were compared to pressures predicted using the Moldflow flow‐analysis programs. Correlation between experimental and predicted pressures was good provided that accurate input data to the computer programs were used. The choice of runner diameter in the approximation of the irregular shaped runner of this tensile bar mold was found to be important, since the runner length was approximately 40 percent of the total flow length. Material properties of particular importance were thermal conductivity, viscosity, and no‐flow temperature (the temperature at which the resin will no longer flow). Viscosity/shear rate/temperature data are needed for the computer programs and two methods of obtaining the data were examined: an Instron capillary rheometer and a capillary nozzle on an injection‐molding machine. Good agreement between the two methods was found for polypropylene over a shear rate range of 100 to 10,000 s−1. Only the injection‐molding capillary nozzle could be used for the nylon‐ and glass‐filled nylon due to the thermal degradation that occurred in th

ISSN:0032-3888    

DOI:10.1002/pen.760240709

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractAn experimental study was made of the effects of die geometry and extrusion velocity on parison swell for three high‐density‐polyethylene blowmolding resins. Four annular dies were used: a straight, a diverging, and two converging dies. Diameter and thickness swells were measured as functions of time under isothermal conditions and in the absence of drawdown. This was accomplished by extruding into an oil having the same density and temperature as the extrudate. It was observed that 60 to 80 percent of the swell occurs in the first few seconds and that equilibrium swell is attained only after 5 to 8 minutes have elapsed. The diameter and thickness swells appear to be independent phenomena, as the relationship between them depends strongly on die design. The ranking of the resins in terms of the magnitude of the swell was found to be the same for all die geometries and extrusion rates u

ISSN:0032-3888    

DOI:10.1002/pen.760240710

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760240701

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY