The Effect of Variations in Chain Connectivity on Strain-Induced Crystallization in Unvulcanized EPDM Elastomers

1984 ◽  
Vol 57 (4) ◽  
pp. 703-724 ◽  
Author(s):  
B. J. R. Scholtens
Keyword(s):  
Deleterious Effect ◽  
Crystallization Process ◽  
Bond Formation ◽  
Drastic Reduction ◽  
Enhancing Effect ◽  
Strain Induced Crystallization ◽  
The Individual ◽  
Positive Effect ◽  
Induced Crystallization ◽  
Melting Entropy

Abstract The introduction of a small amount of chemical or physical crosslinks has an enhancing effect on SIC in EPDM. This situation results from a decrease in stress relaxation or creep, so that the individual chains are deformed more affinely. At the same time, there is no deleterious effect of crosslinks on the crystallization of nonstretched EPDM because of its copolymeric nature. Therefore, the higher connected chains have a smaller melting entropy upon stretching, which promotes the crystallization process. In both EPDM green rubbers and black compounds, the amount of crystallinity and the end-melting temperature increase considerably with strain, in contrast to literature reports. These are desirable qualities for rubber tack. In spite of the positive effect of a higher chain connectivity on SIC, chain connectivity has a detrimental influence on tack. This effect is the result of a drastic reduction in bond formation caused by diminished material flowability and chain interdiffusion. Hence, we conclude that a tack-grade EPDM should, preferably, contain no branched or lightly crosslinked structures.

Networks with Semiflexible Chains and Networks Exhibiting Strain-Induced Crystallization

1997 ◽  
Author(s):  
Burak Erman ◽  
James E. Mark
Keyword(s):  
Liquid Crystalline ◽  
Aromatic Polyamide ◽  
Polymer Chains ◽  
Flexible Polymer ◽  
Main Emphasis ◽  
Strain Induced Crystallization ◽  
The Subject ◽  
The Individual ◽  
Induced Crystallization

Classical theories of rubber elasticity are based on models of flexible polymer chains that are sufficiently long to exhibit Gaussian behavior as described in chapter 1 and in appendix F. Additionally, the chains are phantomlike in the sense that they do not interact with one other along their contours. The theories described in chapter 2 were based on this picture of the individual chain. In this chapter, we describe the elasticity of networks that depart substantially from those addressed in the classical theories. The departures may result from two sources: (1) the chains may be only semiftexible, as a result of which the segments of neighboring chains compete for space in the deformed network, and choose preferentially oriented configurations, and (2) the chains may form crystallites, upon deformation, as a result of which the homogeneous structure of the classical network model may be transformed into a nonhomogeneous one having microphases of crystalline and amorphous regions. The subject of crystallization under deformation, for networks in general, is relatively old, and has been treated in some detail in previous studies. For this reason, crystallization and some of its effects will be reviewed only briefly at the end of this chapter. The main emphasis will be given to networks with semiflexible chains. Examples of networks with semiflexible chains are those in which the chains have rodlike segments separated by flexible spacers, or those where the chains have bond angles appreciably larger than tetrahedral. Incorporation of these chains into a network structure results in materials that exhibit segmental orientations significantly larger than those shown by classical networks. Specific examples would include networks prepared from aromatic polyamide chains or from chains containing liquid-crystalline sequences along the direction of the backbone. Because of their unique chain structures, these networks are easily orientable, at the molecular level, by macroscopic deformations. The orientational transitions may easily be controlled by application and removal of anisotropic strains, and are therefore of great technological interest for use in optical devices. Other examples of networks with easily orientable chains are those with rigid sequences in the side groups.

Hermeneutic circle in development of methodological culture of future music teacher

2017 ◽  
pp. 154-158
Author(s):  
A. S. Koval
Keyword(s):  
Future Teacher ◽  
Music Teacher ◽  
Basic Principles ◽  
Hermeneutic Circle ◽  
High Culture ◽  
Text Understanding ◽  
Hermeneutic Approach ◽  
The Future ◽  
The Individual ◽  
Positive Effect

This article is devoted to the studying hermeneutic circle in the development of methodological culture of future music teacher. Under the conditions of globalization processes, tendencies of convergence of world cultures improvement of culturological training of student youth requires new approaches, in particular, culturological training of students of pedagogical specialties. The task of pedagogical education is to develop a teacher as a specialist and as a person of high culture, who has a special positive effect on the personality of school student. This article analyses the works of scientists dedicated to the issues of establishment and development of the hermeneutic approach in philosophical, psychological, and logical and gnosiological contexts. It is defined the essence of the concept of “hermeneutic circle” as one of the basic principles of the hermeneutic approach. There have been provided the examples of interpretation of the principle of hermeneutic circle by various scientists. Hermeneutic approach is applied in sciences such as pedagogy, psychology, economics, sociology etc. In pedagogical science the hermeneutic approach at the level of conceptual use was elaborated by A. Zakirova. She introduced the term “pedagogical hermeneutics”. Hermeneutic circle as a principle of text understanding is based on the interrelation of the part and the whole. Understanding of the whole consists of the understanding of the individual parts, and understanding of the parts requires understanding of the whole. The concepts of the part and the whole are correlated: the text is a part concerning the whole creative activity of the author, which in its turn is a part of the particular genre or literature in general, as well as the part of spiritual life and biography of the author. The idea of hermeneutic circle means also that there is no understanding of the text without certain prerequisites: understanding is preceded by some idea of what is yet to understand. There have been determined the peculiarities of the use of the principle of hermeneutic circle in the development of methodological culture of the future teacher of musical art. In light of hermeneutical trends, the penetration of which in the realm of musical art can be traced quite clearly, the use of the hermeneutic circle principle in the development of methodological culture of the future teacher of musical art appears not only in the narrow interpretation of the particular phenomenon or group of phenomena, but much wider — as a means of learning and understanding of the worldview by a person.

Reconstructing the mechanical response of polybutadiene rubber based on micro-structural evolution in strain-temperature space: entropic elasticity and strain-induced crystallization as the bridges

Soft Matter ◽  
2020 ◽  
Vol 16 (2) ◽  
pp. 447-455 ◽  
Author(s):  
Pinzhang Chen ◽  
Yuanfei Lin ◽  
Jingyun Zhao ◽  
Lingpu Meng ◽  
Daoliang Wang ◽  
...  
Keyword(s):  
Mechanical Response ◽  
Structural Evolution ◽  
Entropic Elasticity ◽  
Polybutadiene Rubber ◽  
Strain Induced Crystallization ◽  
Induced Crystallization

Micro-structural evolution of polybutadiene rubber in strain-temperature space, and the reconstruction of the macro-mechanical response.

scholarly journals Responsiveness of the Scripps Neurologic Rating Scale During a Multiple Sclerosis Clinical Trial

1999 ◽  
Vol 26 (4) ◽  
pp. 283-289 ◽  
Author(s):  
James A. Koziol ◽  
Adriana Lucero ◽  
Jack C. Sipe ◽  
John S. Romine ◽  
Ernest Beutler
Keyword(s):  
Multiple Sclerosis ◽  
Clinical Trial ◽  
Rating Scale ◽  
Effect Sizes ◽  
Active Therapy ◽  
Double Blind ◽  
Treatment Groups ◽  
Negative Effect ◽  
The Individual ◽  
Positive Effect

Objective:The Scripps neurologic rating scale (SNRS) is a summary measure of individual components comprising a neurological examination, designed for use in multiple sclerosis (MS). Our objective is to evaluate the responsiveness of the SNRS, within the context of a 2-year, randomized, double-blind crossover study of the efficacy of cladribine for treatment of secondary progressive MS.Methods:Effect sizes were determined for the SNRS and its components, separately for each treatment group (initial placebo, and initial cladribine) over both years of the clinical trial, using a standard random effects model.Results:Individual components tended to show positive effect sizes (improvement) during periods of active therapy in both treatment groups, and negative effect sizes (deterioration) during periods of no active therapy. Summation indices derived from the individual components of the SNRS seemed somewhat more stable than the individual components. The two components mentation and mood, and bladder, bowel, or sexual dysfunction, were rather unresponsive in our clinical trial.Conclusion:Changes in the components of the SNRS over the course of our clinical trial were consistent between the two treatment groups. Most components were moderately responsive; and, the summary SNRS score appropriately summarized the moderate magnitudes of change evinced in the individual components.

Strain-induced crystallization behaviour of natural rubbers from guayule and rubber dandelion revealed by simultaneous time-resolved WAXD/tensile measurements: indispensable function for sustainable resources

RSC Advances ◽  
2016 ◽  
Vol 6 (98) ◽  
pp. 95601-95610 ◽  
Author(s):  
Yuko Ikeda ◽  
Preeyanuch Junkong ◽  
Takumi Ohashi ◽  
Treethip Phakkeeree ◽  
Yuta Sakaki ◽  
...  
Keyword(s):  
Natural Rubber ◽  
Crystallization Behaviour ◽  
Time Resolved ◽  
Sustainable Resources ◽  
Strain Induced Crystallization ◽  
Induced Crystallization

Guayule and rubber dandelion natural rubbers are useful alternatives forHeveanatural rubber in terms of their strain-induced crystallization behaviours.

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