摘要:

AbstractConsiderable progress has been made in the past 20 years in the synthesis, characterization and fabrication of plastics. Previous SPE Award winners, such as Mark, Natta, and Marvel dealt largely with synthesis; Flory with characterization; Alfrey and Du Bois with fabrication. One of the still unsolved problems lies in the realm of relating mechanical properties, such as impact strenght and creep to molecular structure.The design enginner who wishes to use a plastic part is concerned primarily with how some property such as impact strenght varies with temperature, speed of test, test method, etc. The polymer scientist must know why. Through knowing why, he may be able to design better plastics.This paper attempts to survey some of the world‐wide progress made in this area in the past 10 years. The ultimate goal is to understand these mechanical properties in terms of internal molecular motions which occur in solid polymers. Internal motion can be detected by electrical, electromagnetic and dynamic mechanical measurements. When these three methods are applied on a given polymer over a range of temperatures, insights can be gained as to the variation of impact strength and other properties with temperature and frequency for that same polymer. These three fundamental methods, which require very small samples (less than 50 grams), can provide insight into the practical behavior of plastic materials over the wide range of temperatures and frequencies encountered in the real worl

ISSN:0032-3888    

DOI:10.1002/pen.760080302

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

摘要:

AbstractAn experimental study of the tensile modulus of unidirectional short fiber reinforced plastics is reported. The data show poor agreement with the theories for the longitudinal case but better agreement in the other cases. A semi‐empirical theory is proposed to explain the longitudinal modulus dat

ISSN:0032-3888    

DOI:10.1002/pen.760080303

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

摘要:

AbstractAn experimental study of the tensile strength of unidirectional short fiber reinforced plastics is reported. The data indicate agreement with existing theories as modified to suit plastics. The theory is extrapolated to provide a means for computing the strength of a random composite.

ISSN:0032-3888    

DOI:10.1002/pen.760080304

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

摘要:

AbstractThe morphology of the quenched form of polypropylene was investigated. Thin films of the quenched form consist of small ball‐like structures which we suggest are defective hexagonal crystals. In thicker films they aggregate to form spherulites with no observable fine structure. Quenching of thin films of molten polypropylene to a temperature below 0°C results in the formation of numerous, isolated monoclinic spherulites with a better defined morphology than the smectic spherulites obtained by quenching above 0°C. This result suggests that the films (quenched below 0°C) were quenched to the glass and subsequently crystallized to the monoclinic form upon heating to room tempera

ISSN:0032-3888    

DOI:10.1002/pen.760080305

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

摘要:

AbstractThe physical properties, i. e., yield stress and stress‐strain curve of the quenched (“smectic”) form of polypropylene have been shown to be time dependent at room temperature. The yield stress increases linearly with the logarithm of film age. No changes in the x‐ray diffraction pattern, infra‐red spectrum, electron diffraction pattern or morphology have been observed corresponding to this change in physical properties. A molecular mechanism is proposed which will explain this again process. Spherulites of the quenched form have been found to deform affinely when drawn. In contrast to this, slow cooled films show complete destruction of internal spherulite (lamellar) order, indicating a complex mechanism of de

ISSN:0032-3888    

DOI:10.1002/pen.760080306

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

摘要:

AbstractPhysical and mechanical properties of block copolymers are compared and correlated with the corresponding random copolymers. The important properties of melting point, transition temperatures, tensile strength, modulus, and elastic properties depend upon the structural arrangement of the molecular units comprising the polymer strecture. All available data suggest overwhelmingly that properties of block copolymers are superior to those of random copolymers. A block copolymer can have properties characteristic of each of the homopolymers from which it is derived as well as a set of properties due to the polymer strcture as a whole. Block copolymers have an advantage over random copolymers in that a crystalline polymer can be modified without significant reduction of its melting point, modulus, tensile strength, and elastic properties, and by suitable selection of a second component it affords a means of “building in” a particular prope

ISSN:0032-3888    

DOI:10.1002/pen.760080307

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

摘要:

AbstractSpiral and helical fractures can be formed around high‐modulus filaments and yarns which are embedded in brittle, amorphous, crosslinked resins. The phenomena are of particular interest because the stress field imposes a highly regular geometry upon the propagating fractures, and because the formation of the large surface area of the spiral fractures provides an efficient mechanism for dissipating strain energy. Development of the approach of the production of discrete geometrical voids with large surface area at predicatable sites may well provide resistance to impact in inherently brittle material

ISSN:0032-3888    

DOI:10.1002/pen.760080308

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

摘要:

AbstractA knowledge of the variation of melt viscosity of thermoplastic polymers with both shear rate and temperature is of considerable importance to plastics engineers as well as to polymer rheologists. The actual measurement of melt viscosity at a large number of temperatures and shear rates is frequently a tedious and time‐consuming task. A technique has been developed, based upon the applicability of shear rate‐temperature superposition, for predicting the flow curves of a number of olefin polymers and copolymers at various temperatures from experimental data obtained at one temperature for the material in question. The experimental validity for superimposing log shear stress—log shear rate curves at different temperatures along the log shear rate axis has been established for both high and low density polyethylenes, polypropylene, polybutene‐1, and poly (ethylene vinyl acetate) copolymers. The temperature dependence of the resultant shift factors has been determined for each system, and the method of utilizing this information to predict viscosities as a function of temperature and shear rate is di

ISSN:0032-3888    

DOI:10.1002/pen.760080309

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

摘要:

AbstractA widely accepted method for determining the particle size of the dispersed phase in impact polystyrene is by the microscopic examination of microtomed sections or dilute solutions of the polymer. Although this technique is relatively quick, it has obvious shortcomings to its statistical relaibility. In an effort to obtain more meaningful data, a Coulter Counter was employed to measure the average particle size and particle size distribution of the dispersed phase in a number of impact polystyrene samples. The materials examined contained rubber particles ranging from one to twenty microns in diameter. It was found that the weight average distribution of these particles was most nearly described by a log‐normal probability function. The relative accuracy and reproducibility of the measurements made with the Coulter Counter suggest that it is a valuable tool for obtaining quantitative particle size information on the rubber modified polystyrene syste

ISSN:0032-3888    

DOI:10.1002/pen.760080310

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760080301

出版商:Society of Plastics Engineers, Inc.    

年代:1968

数据来源: WILEY