摘要:

AbstractGiven the numerous variables in composition, reaction conditions, and processing, the design of a polyurethane elastomer with a specified set of properties is indeed a challenging task. The control of characteristics such as heat stability, toughness, fatigue, and other key qualities requires a compendium of theoretical and experimental knowledge. Optimizing a single property, e.g., low temperature resiliency, can necessitate changes in composition that may compromise other important properties. Thus, to balance the entire system in order to meet the specification limits, much more than an empirical approach is needed to achieve the goal in a reasonable time. In this presentation, we will demonstrate that, by use of an array of sophisticated testing methods and carefully designed experiments combined with computer modeling, the tailoring of a segmented elastomer can be placed on a scientific basis. Key methods of characterization are dynamic mechanical spectroscopy, small angle X‐ray scattering, electron microscopy, Fourier transform infrared, and differential scanning calorimetry. Special experiments included the systematic synthesis and testing of a wide range of model compounds. Optimum soft segment properties such as chain length and mobility were defined. Hard segments that are properly segregated and have high thermal and mechanical integrity were synthesized and characterized. These and related experiments have led us to a better understanding of the molecular mechanisms underlying the mechanical and thermal behavior of an elastomer. With this knowledge we can select molecular components and control phase relationships in building elastomers to meet end use requirements that demand maximum static and dynamic polymer propertie

ISSN:0360-8905    

DOI:10.1002/polc.5070720133

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractEnhancement of polymer properties by controlling supramolecular structure during fabrication was of major interest to Turner Alfrey. Supramolecular structure, i.e., the geometric arrangement of macromolecules in a specimen, is established during mechanical processing and can have a profound effect on properties. Several examples of Alfrey's contributions to fabrication of polymers are reviewed which demonstrate the Alfrey method of analyzing complicated fabrication processes.

ISSN:0360-8905    

DOI:10.1002/polc.5070720134

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractItems fabricated from thermoplastics containing short glass fibers are anisotropic and the anisotropy varies from point to point. Guidance as to how such materials should be evaluated and what data are required for the design of end products molded from them is provided by a combination of the theories of viscoelasticity and anisotropic elasticity, whereby the stiffness and compliance coefficients of the latter are functions of time, temperature, and strain. A methodology then emerges, similar in overall nature to that pertaining to thermosetting resins containing long aligned fibers, but rather more complex because of the variations in fiber alignment. However, an adequately comprehensive evaluation in accordance with the formal rationale tends to be prohibitively expensive and, on the other hand, a curtailed evaluation can yield misleading data. Recent work aimed at resolving that impasse seems promising. The central principle is the use of special test specimens chosen because their flow geometries and possible flow irregularities are similar to those commonly found in commercial end products. The data that can be derived from such specimens can be related quantitatively to those derived from the conventional tests, and therefore the presentation and use of the new class of data entail no interpretation difficulties. Examples of what has been achieved and speculations about what might further be achieved are presented in the paper.

ISSN:0360-8905    

DOI:10.1002/polc.5070720135

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractLatest injection molding machines are often equipped with process control computers monitoring and controlling operating sequence, injection speed, holding pressure, clamping motion, clamping force, and all temperatures. This provides for the possibility to overlay process‐related optimization programs for adaptation of the machine to the respective material condition and programs for the machine control. The following pages inform about such optimization program

ISSN:0360-8905    

DOI:10.1002/polc.5070720136

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractIn 1963 Boyer proposed the existence of a liquid‐liquid transition, Tll, in polystyrene above the glass transition Tg. Since that time there has been considerable discussion and disagreement on the existence of this transition. Detailed shear modulus data as a function of temperature in the range 165–215°C will be presented for a series of polystyrenes of various molecular weights. In each case, as the temperature is increased, the modulus gradually decreases until a specific molecular weight dependent temperature is reached and then suddenly the modulus decreases rapidly over a few °C and then returns to its previous gradual decrease with increasing temperature. The response is reminiscent of the modulus behavior going through Tg. It is suggested that the temperature at which this sharp decreased in modulus takes place is Tll. The molecular weight effects on Tllwill be discussed in terms of several rheological properties that measure the temperature of this trans

ISSN:0360-8905    

DOI:10.1002/polc.5070720137

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractWithin the past several years considerable interest has developed in the practice of retrofitting of plasticating extruders with gear pumps. The primary motivation for this is to reduce surges and fluctuations in the extrusion rate, thereby improving product quality and reducing waste. It is shown that the effectiveness of a gear pump for this purpose is directly related to its volumetric efficiency. The volumetric efficiency depends upon the pump dimensions, the flow behavior of the polymer, and the operating variables of temperature, pressure, and pump speed. Experimental data on a variety of thermoplastic materials has been obtained using a pump with gear wheels of 3.6 cm diameter. These data have been correlated with an empirical equation. Some tentative conclusions are drawn concerning the sizing of gear pumps for specific applications.

ISSN:0360-8905    

DOI:10.1002/polc.5070720138

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe molding of fiber‐reinforced thermoset components is a complex process involving a highly exothermic chemical reaction which takes place in the presence of flow and thermal gradients. The flow in turn is complicated by time and temperature‐dependent rheological characteristics. The industry has grown largely on the basis of empirical developments. However, numerous problems do remain which required increased understanding for solution. This report reviews work underway in numerous laboratories to characterize the flow and cure of SMC and phenomena associated with these processes such as orientation, mechanical properties, residual internal stresses, mold fill, and surface defe

ISSN:0360-8905    

DOI:10.1002/polc.5070720139

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

ISSN:0360-8905    

DOI:10.1002/polc.5070720140

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

ISSN:0360-8905    

DOI:10.1002/polc.5070720102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY