摘要:

AbstractGlassy polycarbonate specimens with different degrees of aging were tested in puncture for the purpose of determining the ductile/brittle transition temperature in biaxial tension. The results show that increasing amounts of aging increase the transition temperature from −95 to −70°C. All transitions appear too low In temperature. This was confirmed by using strip‐biaxial specimens that become brittle at a significantly higher temperature. In addition to this problem, the load deflection curve also can lead to an overestimation of the load and energy to initiate cracking. A finite element model of the puncture test suggests that the compressive stress under the dart may have shifted the onset of brittleness to much lower temper

ISSN:0032-3888    

DOI:10.1002/pen.760271102

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThe relationships between equilibrium melting temperatures (Tm*) and crystalline morphology of poly[3,3bis(ethoxymethyl)oxetane], (polyBEMO), poly[3,3‐bis (azidomethyl)oxetane], (polyBAMO), and poly(ethylene oxide), (PEO), were characterized. The Hoffman‐Weeks extrapolation procedure led toTm* values of 92, 102, and 69°C for these three polymers, respectively. The gross morphologies of polyBEMO, polyBAMO, and PEO were studied as a function of melt‐liquid temperature (Ti) and isothermal crystallization temperature (Tc) by visible light microscopy. Spherulitic morphologies were observed for polyBEMO, polyBAMO, and PEO whenTiwas aboveTm*, while nonspherulitic (hedritic) morphologies were observed atTls belowTm*. Mixed morphologies were observed whenTlwas approximately equal

ISSN:0032-3888    

DOI:10.1002/pen.760271103

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractCuring reactions of epoxy resins are accelerated by added hydrogen‐bond donor solvent and hydroxyl groups produced during the course of polymerization. A kinetic model comprising several different polycondensation and polyaddition reactions that occur simultaneously is developed. The concept of diffusion controlled reactions is employed to describe the change of reaction rate constants with conversion after the formation of an infinite crosslinking network. Good agreement is obtained between the model predictions and experimental data available in the literatur

ISSN:0032-3888    

DOI:10.1002/pen.760271104

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractIn the present work, fusion behavior, crystallinity, and mechanical properties of beverage bottle poly(ethylene terephthalate) (PET) was compared with those of the virgin material. Viscosimetry measurements, differential scanning calorimetric studies, impact and tensile determinations were made in both materials. The lowerMvof bottle PET revealed that a thermomechanical degradation occurred during processing. Although bottles possess a considerable degree of crystallinity (≈30 percent), the crystallites are so small that they don't scatter light and, therefore, bottles are transparent. Virgin PET exhibited a brittle behavior while bottle PET exhibited a ductile one. This is a consequence of the difference In crystallinity between both materials (greater for virgin PET because of its original higher crystallinity content), although they were molded under the same conditions. Such difference was attributable to a “crystalline memory” effect having its origin in the orientation of the material during Injection molding at low temperature (250°C). Injection‐molded PET specimens showed a strong, crystalline memory, capable of crystallization during very fast qu

ISSN:0032-3888    

DOI:10.1002/pen.760271105

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThe specific essential works of plane stress ductile tearing of several high‐ and ultrahigh‐molecular‐weight polyethylenes were obtained from deeply edge‐notched tension specimens, with either single or double notches, by extrapolating the straight line relationship between the total specific fracture work and ligament length to zero ligament. Provided the fracture morphologies of the torn ligament are not widely different, the specific essential work (we) is a material property dependent on thickness but independent of specimen geometry. The specific essential fracture work also can be identified withJcthe critical value of theJ‐integral along a contour immediately bordering the fracture process zone at the crack tip. There is good agreement between the experimental we values and theoreticalJcestimates for these polyethylene

ISSN:0032-3888    

DOI:10.1002/pen.760271106

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThe temperature dependence of the Newtonian viscosity, ηo(T), of four structurally related amorphous thermoplastics (polyarylate, polysulfone, polycarbonate, and phenoxy) was measured in the temperature region betweenTgand (Tg+ 100 K) by means of a parallel plate technique. This offers a simple and quick alternate mode of measurement to traditional techniques. Values of ηo(T) measured, as well as some data obtained from literature and corresponding to theT>(Tg+ 100 K) range, were fitted to Vogel‐Fulcher expressions. Fractional free volume atTgwas evaluated from Vogel‐Fulcher parameters. The values obtained are similar for all polymers studied, and they are greater than those normally observed for other amorphous polymeric systems that are structurally simpler. From the results obtained we can conclude that the rheological behavior and, hence, the chain “stiffness” of polyarylate, polysulfone, and polycarbonate, at the temperature range of industrial processing, are very similar. However, phenoxy, which contains a greater number of nonaromatic flexible structures in its chain, has a different behavior with a lower activation energy for viscous flow in the same range of te

ISSN:0032-3888    

DOI:10.1002/pen.760271107

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper is concerned with the effect of thermal history on the rheology of three liquid crystal copolymers. The polymers were heated to temperatures above their melting points and then cooled down. During the cooling cycle, the dynamic mechanical properties were monitored. It was found that these properties remained unchanged at temperatures as low as 30°C below the normal melting points for two copolyesters of 60 mole percent p‐hydroxybenzoic acid (PHB) and 40 mole percent poly(ethylene terephthalate) (PET) (60‐40 PHB/PET) and 80 mole percent PHB and 20 mole percent PET (80‐20 PHB/PET). For a copolymer of PHB and 2,6‐dihydroxynaphthaic acid, there was a gradual increase in the properties with decreasing temperature. However, at a critical temperature all three systems exhibit a sudden increase In dynamic mechanical properties. The kinetics of solidification were also monitored, and it was found that at temperatures well below the melting point, it took 4 to 6 min before the solidification process impeded flow. Extrusion studies on these materials were also carried out, and it was observed that in this supercooled state, the polymers exhibited significant die swell. The samples also exhibited a fibrous texture and were more oriented than when extruded isothermally above the melti

ISSN:0032-3888    

DOI:10.1002/pen.760271108

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractUntaxial tension tests to the yield point were performed on polypropylene as a function of temperature from 22 to 143°C at a strain rate of 2 min−1. At 22, 42, and 71°C, measurements were also made at strain rates from 0.02 to 8 min−1. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (164°C). The ratio of thermal to mechanical energy to produce yielding is about three times smaller than for glassy polymers. The ratio of yield stress to (initial) Young's modulus is about 0.024 at room temperature and increases to 0.043 at 143°C. Yield stress is a linear function of unstrained

ISSN:0032-3888    

DOI:10.1002/pen.760271109

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractTo przoduce efficiently high quality structural parts from fiber‐reinforced epoxy materials systems, it is necessary to develop detailed process models. One key component in any such model involves the prediction of the cure kinetics, which in turn governs the viscosity, resin flow, void formation, and other important processing parameters. In this study, a series of isothermal and dynamic differential scanning calorimetry experiments was performed using Hercules 3501‐6 and 3502 resins (TGDDM epoxy with DDS curing agent). The hypothesis of a dispersion of growing microgel particles, which become a continuous‐phase solid at the gel point, was used as a basis to apply the Avrami theory of phase change to describe the polymerization kinetics up to the gel point. The extended equations for nonisothermal conditions properly accounted for the temperature effects on the kinetics. Comparison of the theoretical predictions with experimental data suggests that the Avrami theory of phase change may model adequately the cure kinetics of these systems, at least up to the gel

ISSN:0032-3888    

DOI:10.1002/pen.760271110

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThe mutual diffusion coefficients for three molten polystyrene(PS)‐hydrocarbon systems—PS‐in‐xylene, PS‐n‐octane, and PS‐n‐nonane—were measured by using a sorption apparatus with quartz spring in the temperature region from 130 to 175°C and for mass fraction of hydrocarbon ranging from 0 to 0.15. The mutual diffusion coefficients were correlated with good agreement by the

ISSN:0032-3888    

DOI:10.1002/pen.760271111

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY