摘要:

AbstractThis review aims to encompass various situations where optical microscopy—particularly observation and measurement of birefringence—can be used to deduce the nature of intermolecular correlations in polymers. The necessary background dealing with light propagation in anisotropic media is summarized in practical terms. The review is especially concerned with illustrating how unjustified assumptions and ambiguous terminology can cause erroneous interpretation of results. Many references cited are themselves reviews or even textbooks; they afford detailed access to the wide and diffuse literature that full coverage of this subject demands, but would constitute an unwieldly bibliography if listed as individual publicati

ISSN:0032-3888    

DOI:10.1002/pen.760261502

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractIn this study, optimal temperature profiles (or histories),T(t), are obtained for nonvaporizing plug‐flow (or batch) Nylon 6 reactors using the minimum principle. Two objective functions are studied, one in which the monomer conversion,convtf, is maximized, and the other in which the undesirable side product (cyclic dimer) concentration in the output stream, [C2]tf, is minimized. The control variable, temperature, is constrained to lie between 220°C and 270°C in order to ensure single phase polymerization. The most significant difference between this study and earlier ones is that the residence (or reaction), timetf, is not specifieda priori, but is determined optimally by the use of a ‘stopping’ condition such that the polymer product has a number‐average chain length, μn, equal to some desired value μn.d. Simultaneously, an end‐point constraint is used, which, depending on the objective function used, forces either the cyclic dimer concentration or the monomer conversion at the end of the reactor to lie at a specified value, [C2]dorconvd. Thus, this algorithm incorporates stopping conditions as well as end‐point constraints and so is more complex than earlier ones, but the results are more meaningful. Different nonisothermal optimal temperature profiles are obtained for the two objective functions studied, depending on the values of μn.d,convd, [C2]d, and the feed water concentration, representing the complex interplay of several

ISSN:0032-3888    

DOI:10.1002/pen.760261503

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractExperimental data on hexane vaporsorptionin phase‐segregated polybutadiene/polystyrene blends are reported, which exhibit seemingly non‐Fickian characteristics that previous workers with styrene/butadiene copolymer attributed to a diffuse interphase. These data, plus results derived from a model of sorption in heterogeneous media containing a slowly permeable dispersed phase, indicate that the mere presence of two phases with different diffusion time constants is a sufficient condition for apparently non‐Fickian overall behavior. Consequently, definitive morphological inferences cannot be drawn from such observations. In addition, results of modeling the correspondingpermeationprocess are analogous to those obtained in an earlier study of permeation with immobilizing chemical rea

ISSN:0032-3888    

DOI:10.1002/pen.760261504

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe results of creep and recovery experiments are reported for two types of polyethylene—one a linear high density homopolymer, and the other an ethylene‐hexene copolymer. Data were obtained at temperatures in the range 23°C to 57°C and creep times of 10 s to 4.33 × 105s. In order to approximate constant true stress conditions, all of the experiments were carried out at the same value of applied stress (4 MPa) and the change in strain during creep was in all cases less than 2 percent. Comparison of these results with the results from earlier work on an ultra high molecular weight polyethylene shows that there is a great similarity in the behavior of all three materials, and the behavior of all three can be described quite well by a one‐dimensional equation consisting of two terms—one a hereditary term and the other a plasticity term. It is further shown that to a very good approximation the idea of time‐temperature superposition can be applied to the description of the her

ISSN:0032-3888    

DOI:10.1002/pen.760261505

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe adiabatic temperature changes for poly(methyl methacrylate) (PMMA) and high‐density polyethylene are reported as the result of rapid compressive stress applications at different temperatures. A specially‐modified Instron capillary rheometer was used in the experiments. Results were examined by determining the experimental thermoelastic coefficients (δT/δ). These were compared with the predicted coefficients from the equation (δT/δ) = ∝LTo/ρCp. Good agreement was found for ambient temperature, and deviations were found for higher temperatures. High‐density polyethylene showed higher temperature changes than PMMA, the causes for which are al

ISSN:0032-3888    

DOI:10.1002/pen.760261506

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractWe studied the integral sorption of saturated, organic vapors in amorphous films of poly (ethylene terephthalate) (PET) using a spring balance apparatus. The penetrants employed (methylene chloride [MeCl2] and N. N. dimethyl formamide [DMF]) induce substantial crystallization of the polymer during sorption. The experimental data (mass of vapor absorbed versus exposure time) do not obey Fick's law for diffusion but reflect the influence of time dependent polymer swelling and crystallization. The data show that polymer swelling controls the penetrant transport in thin films, while molecular diffusion in the highly swollen semi‐crystalline polymer controls in thick films. Small activation energies were found for transport in thin films suggesting that ductile deformation controls the swelling in PET. A mathematical model developed previously explains the important features of the experiment

ISSN:0032-3888    

DOI:10.1002/pen.760261507

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe influence of cryo‐ground rubber (CGR) on melt flow and mechanical properties of polypropylene has been investigated. Cryo‐ground rubber was incorporated in the polypropylene matrix (a) in powder form and (b) as masterbatch with natural rubber. Natural rubber was found essential as a dispersing agent. The loading of cryo‐ground rubber has no significant effect on viscosity at high shear rates (>61 s−1) but at lower shear rates (>61 s−1), viscosity functions change shape with increasing cryo‐ground rubber content. The dynamic mechanical properties revealed that polypropylene is thermodynamically incompatible with natural rubber and cryo‐ground rubber. Cryo‐ground rubber in the powder form shows poor adhesion to polypropylene matrix and, therefore, decreases the impact strength at higher loading. Addition of masterbatch of cryo‐ground rubber and natural rubber improves the impact strength

ISSN:0032-3888    

DOI:10.1002/pen.760261508

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760261501

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY