Mechanism of the Crystallization of High Polymers

1954 ◽  
Vol 27 (2) ◽  
pp. 374-384 ◽  
Author(s):  
G. Schuur
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Amorphous Material ◽  
Crystalline Polymer ◽  
Longitudinal Direction ◽  
Crystalline Material ◽  
Current View ◽  
X Ray ◽  
Made In ◽  
High Polymers

Abstract The crystallization of higher polymers is a phenomenon which is not yet fully understood, one of the main difficulties being to explain how the spherulites arise. An attempt will be made in this paper to draw a clearer picture of the mechanism of crystallization and thus to account for the origin of spherulites. It will then be seen how several other phenomena involved in the crystallization of natural rubber can be shown to be logically interrelated. The current view is that a crystalline polymer consists of a continuous amorphous phase containing small crystalline regions, the crystallites. The evidence as to the size of these crystallites, however, is at present inconclusive, because only the lower limit of their size can be measured by means of x-ray examination. The reason is that, owing to the absence of reflections of a higher order, the effect of irregularities in the crystallites and of the heat motion of the molecules cannot be measured separately. Another doubtful question is whether the small angle interference maxima are to be interpreted as a measure of mean distances between the crystallites. To do this, Wallner has to resort to the assumption that the crystallites are unstable, whereas it is presumed, on the evidence of the mechanical properties of the high polymers, that a crystallite is stable and permanent. Hoffmann found 82 ± 7 per cent of crystalline material in polychlorotrifluoroethylene and Buckley, Cross, and Ray found as much as 95 per cent in polymethylene. Such high percentages make it doubtful whether the crystalline phase can be discontinuous at all. In this article any volume of material in which the molecules lie parallel is called a crystallite. The direction in which the molecules are oriented is termed the longitudinal direction of the crystallite. It is immaterial to the argument whether a crystallite consists of several crystallites, aligned in parallel separated by a small amount of amorphous material, or of a single crystallite containing large irregularities.

SYNERGISTIC REINFORCEMENT OF ORGANOCLAY AND DOUBLE NETWORKING IN NATURAL RUBBER

2013 ◽  
Vol 86 (2) ◽  
pp. 205-217 ◽  
Author(s):  
Hedayatollah Sadeghi Ghari ◽  
Zahra Shakouri
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Natural Rubber ◽  
Physical And Mechanical Properties ◽  
X Ray Diffraction ◽  
Double Network ◽  
X Ray ◽  
Extension Ratio ◽  
Curing Characteristics ◽  
Scanning Electron

ABSTRACT Research was undertaken on natural rubber (NR) nanocomposites with organoclays. A double-network (DN) structure is formed when a partially cross-linked elastomer is further cross-linked during a state of strain. Two methods were used in the preparation of NR/organoclay nanocomposites: the ordinary method (single-network NR nanocomposite) and double-networked NR (DN-NR) nanocomposites. The single-networked NR nanocomposites were used for comparison. The effects of organoclay (5 phr) with a different extension ratio on curing characteristics, mechanical properties, hardness, swelling behavior, and morphology of single- and double-networked NR nanocomposites were studied. The results showed that double-networked NR nanocomposites exhibited higher physical and mechanical properties. The tensile strength of DN-NR nanocomposites increased up to 33 MPa (more than four times greater than that of pure NR) and then decreased with an increasing extension ratio. Modulus and hardness continuously increased with an increased extension ratio. The microstructure of the NR/organoclay systems was studied by X-ray diffraction and field emission scanning electron microscopy. The effects of different extension ratios on the dispersion of organoclay layers in the nanocomposites were investigated. Generally, results showed that the optimized extension ratio in DN nanocomposites was equal (or about or around) to α= 2.

scholarly journals Экспериментальное определение механических свойств анодного элемента рентгеновского литографа

2020 ◽  
Vol 90 (11) ◽  
pp. 1838
Author(s):  
Н.А. Дюжев ◽  
Е.Э. Гусев ◽  
А.А. Дедкова ◽  
Д.А. Товарнов ◽  
М.А. Махиборода
Keyword(s):  
Mechanical Properties ◽  
Mechanical Strength ◽  
Membrane Structure ◽  
Critical Pressure ◽  
Group Technology ◽  
Analytical Calculation ◽  
Mechanical Stresses ◽  
New Model ◽  
X Ray ◽  
Made In

An anode element of an X-ray lithograph is made in the form of a PolySi/Si3N4/SiO2 membrane structure using group technology. The construction of the stand is modernized to determine mechanical properties of membranes. The critical pressure of membrane structure with a diameter of 250 um varies in the range from 0.484 to 0.56 MPa for 15 samples. The mechanical strength of PolySi/Si3N4/SiO2 structure is 3.13 GPa. The new model in Comsol package shows a good correlation between experimental critical pressure and theoretical mechanical strength of membrane. The distribution of mechanical stresses across membrane by means of modeling and analytical calculation is presented. It is proved that the region of structure discontinuity is localized at membrane/substrate interface.

Mechanical and Swelling Behavior of Double Networked Natural Rubber Cured Using a New Binary Accelerator System

2007 ◽  
Vol 80 (5) ◽  
pp. 809-819 ◽  
Author(s):  
C. V. Marykutty ◽  
G. Mathew ◽  
Sabu Thomas
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Transverse Direction ◽  
Tensile Elongation ◽  
Longitudinal Direction ◽  
Chain Orientation ◽  
Swelling Studies ◽  
Natural Rubber Vulcanizates ◽  
Double Networks ◽  
Accelerator System

Abstract The concept of double networks, which impart chain orientation to elastomers, is a rather new idea. Double networks were induced in natural rubber vulcanizates cured with different accelerator systems. Double networked natural rubber with different extensions cured with N-cyclohexyl benzothiazyl sulphenamide (CBS) and 1-phenyl 5-ortho -tolyl 2,4 dithiobiuret was studied and the effect of extension on the mechanical properties and swelling was analyzed. The extent of chain orientation was analyzed through anisotropic swelling studies. The modulus, tensile strength and tear strength showed an increase with increased residual extension ratio. The effect was more predominant in the longitudinal direction than in the transverse direction. The ultimate tensile elongation showed a slight deterioration. It was revealed that the formation of double networks with higher residual extension ratios restricted the entry of the solvent. Based on the studies it was concluded that residual extension has a profound effect in determining the final properties of vulcanizates.

HAF/SILICA/NANOCLAY “TERNARY” MASTERBATCH AND HAF/SILICA BINARY MASTERBATCH FROM FRESH NATURAL RUBBER LATEX

2014 ◽  
Vol 87 (2) ◽  
pp. 250-263 ◽  
Author(s):  
Sasidharan Krishnan ◽  
Rosamma Alex ◽  
Thomas Kurian
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Carbon Black ◽  
Natural Rubber ◽  
Abrasion Resistance ◽  
Dynamic Properties ◽  
Natural Rubber Latex ◽  
Rubber Latex ◽  
X Ray ◽  
Filler Dispersion

ABSTRACT A process for production of carbon black/silica/nanoclay ternary filler masterbatch from fresh natural rubber (NR) latex was standardized. The fillers, nanoclay, carbon black, and silica were incorporated in fresh NR latex by a modified coagulation process. The latex, mixed with filler dispersions, coagulated immediately on addition of acids. The coagulum containing fillers was dried at 70 °C in an air oven to get the latex filler masterbatch, which was further processed in the conventional way. The masterbatch compounds containing only silica/carbon black showed a higher level of vulcanization as compared with the corresponding dry mixes. The mechanical properties, such as tensile strength, modulus, tear strength, abrasion resistance, and hardness, increased with the proportion of nanoclay in the mixes up to 5 phr, and with a greater amount, the change was only marginal. Lower tan delta values were observed for all of the masterbatches containing nanoclay in the ranges of 3 to 10 phr compared with the control dry mix containing 25/25 carbon black/silica. The improvement in mechanical properties and dynamic properties shown by the masterbatches over the conventional mill-mixed compounds was attributed to factors related to filler dispersion, as evidenced from the data from dispersion analyzer images, X-ray diffractograms, and a higher level of vulcanization.

The crystal structure of polyethylene terephthalate

1954 ◽  
Vol 226 (1167) ◽  
pp. 531-542 ◽  
Keyword(s):  
Crystal Structure ◽  
Polyethylene Terephthalate ◽  
Amorphous Material ◽  
Synthesis Method ◽  
Crystalline Material ◽  
Crystallographic Direction ◽  
Cohesion Energy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Strong Forces

The crystal structure of polyethylene terephthalate (Terylene) has been determined by the interpretation of the X-ray diffraction patterns given by drawn fibres. The unit cell, which contains one chemical unit, —CO.C 6 H 4 .CO.O.(CH 2 ) 2 O—, is triclinic, with a = 4.56Å, b = 5.94 Å, c = 10.75 Å, α = 98 1/2°, β = 118°, γ = 112°. This gives the density of the crystals as 1.455 g/cm 3 . If it is assumed that the density of amorphous regions in partly crystalline material is the same as that of the entirely amorphous material (1.335), the proportion by weight of crystals in ordinary drawn yarn (density 1.39) is 48%, and in specimens of the highest recorded density (1.41) it is 64.5%. These figures are, however, lower limits; if, as is likely, the density of amorphous regions in partly crystalline specimens is lower than 1.335, the proportions of crystalline material are higher than the figures given. The positions of atoms in the crystals have been deduced from the relative intensities of X-ray diffractions; approximate positions were found by trial-and-error methods, and refinement was then effected by calculations of electron densities, using the three-dimensional Fourier synthesis method. The molecules are nearly planar in configuration. Distances between atoms in neighbouring molecules are all normal Van der Waals contact distances; there is therefore no structural evidence for any unusually strong forces between the molecules. This conclusion is in agreement with that based on an estimate of the cohesion energy, which is very nearly the same as that of a comparable aliphatic polyester, polyethylene adipate. The high melting-point of polyethylene terephthalate in comparison with aliphatic polyesters is therefore not due to strong forces between the molecules; it is attributed to the O— ∕ rigidity of the aromatic ring with its attached —C groups. ∖∖ O In most drawn fibres of this polymer, the crystals do not have their c-axes (those parallel to the chain molecules) exactly parallel to the fibre axes; they are tilted in a precisely defined crystallographic direction, such that the 530 plane remains vertical and the inclination of the 001 plane to the fibre axis increases. This is especially well defined in fibres heated to 210° C and allowed to relax, the tilt angle being then about 5°. In principle it is expected that polymer crystals of triclinic symmetry would be tilted, but it is not clear what determines the crystallographic direction of tilt. Tilted crystal X-ray diffraction photographs played an important part in the structure determination.

scholarly journals Silk/Natural Rubber (NR) and 3,4-Dihydroxyphenylalanine (DOPA)-Modified Silk/NR Composites: Synthesis, Secondary Structure, and Mechanical Properties

Molecules ◽  
2020 ◽  
Vol 25 (1) ◽  
pp. 235
Author(s):  
Hiromitsu Sogawa ◽  
Treratanakulwongs Korawit ◽  
Hiroyasu Masunaga ◽  
Keiji Numata
Keyword(s):  
Mechanical Properties ◽  
Secondary Structure ◽  
Natural Rubber ◽  
Chemical Structure ◽  
Attenuated Total Reflection ◽  
X Ray Diffraction ◽  
X Ray ◽  
Superior Mechanical Properties ◽  
Effective Reinforcement ◽  
Β Sheet

Silk composites with natural rubber (NR) were prepared by mixing degummed silk and NR latex solutions. A significant enhancement of the mechanical properties was confirmed for silk/NR composites compared to a NR-only product, indicating that silk can be applied as an effective reinforcement for rubber materials. Attenuated total reflection Fourier transform infrared (ATR-FTIR) and wide-angle X-ray diffraction (WAXD) analysis revealed that a β-sheet structure was formed in the NR matrix by increasing the silk content above 20 wt%. Then, 3,4-dihydroxyphenylalanine (DOPA)-modified silk was also blended with NR to give a DOPA-silk/NR composite, which showed superior mechanical properties to those of the unmodified silk-based composite. Not only the chemical structure but also the dominant secondary structure of silk in the composite was changed after DOPA modification. It was concluded that both the efficient adhesion property of DOPA residue and the secondary structure change improved the compatibility of silk and NR, resulting in the enhanced mechanical properties of the formed composite. The knowledge obtained herein should contribute to the development of the fabrication of novel silk-based elastic materials.

Influence of the Temperature of Crystallization on the Melting of Crystalline Rubber

1941 ◽  
Vol 14 (3) ◽  
pp. 544-545 ◽  
Author(s):  
Norman Bekkedahl ◽  
Lawrence A. Wood
Keyword(s):  
Mechanical Properties ◽  
Crystalline Material ◽  
X Ray Diffraction ◽  
Volume Increase ◽  
X Ray ◽  
Different Temperatures ◽  
Quantitative Results ◽  
Rate Of Heating ◽  
One Year ◽  
Time Required

Abstract Data presented in this communication show an instance in which melting of a crystalline material is very much dependent on the temperature at which the crystals have been formed. It is well known that many substances in which crystallization is relatively slow can be crystallized at different temperatures in a range below the melting point, but no effect of the crystallization temperature on the temperature of melting seems to have been previously reported. The quantitative results for crystalline rubber, the material under investigation, are shown in Figure 1. The crystallization of unvulcanized rubber in the unstretched state has been found to occur at temperatures between about −40° C and 13° C. The time required for crystallization is about one year at 13° C, about ten days at 0° C, and a few hours at −20° C. Below −40° C the mobility is presumably insufficient for the formation of crystals. Crystallization and fusion are accompanied by changes in volume, heat capacity, light absorption, birefringence, x-ray diffraction, and mechanical properties such as hardness. The volume decreases about 2.5 per cent on crystallization, and the magnitude of the change is little influenced, if at all, by the temperature. Fusion, as measured by the volume increase, is found to be independent of the rate of heating, and to occur over a range of five or ten degrees.

scholarly journals Ceramic Waste-Based Natural Rubber Composites: An Exciting Way for Improving Mechanical Properties

2018 ◽  
Vol 4 (3) ◽  
pp. 576-582
Author(s):  
Y.G. Kondarage ◽  
H.M.J.C. Pitawala ◽  
T. Kirushanthi ◽  
D. Edirisinghe ◽  
Thusitha N. Etampawala
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Solid Wastes ◽  
Average Particle ◽  
Gravimetric Analysis ◽  
Ceramic Filler ◽  
Ceramic Particles ◽  
X Ray ◽  
Ceramic Waste ◽  
Micrometer Size

Large amounts of fired ceramic waste produced in ceramic industry do not have a proper method to reuse and mainly thrown away into landfills since fired ceramics have already been sintered and thus their utilization as a raw material is limited. However, these solid wastes have a major environmental and economic concern. Thus, a proper management of such solid wastes is eminent. This research is dedicated to evaluating the possibility of using such ceramic waste as a low-cost filler material in the manufacture of natural rubber based composites. Ceramic particles smaller than 125 μm were selected initially for the preparation natural rubber based composites. For the latter part of the study, particles in sub-micrometer length scales were used. Elemental analyses and composition of the phases of the ceramic particles were determined by X-ray fluorescence and diffraction respectively. The average particle size was characterized by scanning electron microscope (SEM). The surfaces of the sub micrometer size ceramic particles were modified using Silane69 coupling agent. The surface modification was confirmed by Fourier-transform infrared spectroscopy, thermo gravimetric analysis and SEM coupled with energy-dispersive X-ray spectroscopy. Natural rubber based composites were prepared with different levels of ceramic filler loadings. The mechanical properties of the composites such as hardness, resilience, compression set, abrasion volume loss and tensile properties were evaluated. These properties of the composites were compared with those of the composites prepared according to the same formulation except the ceramic filler (control). The composites were found to have an exciting enhancement of mechanical properties with respect to the control. The mechanical property improvement is higher when the ball milled sub-micrometer size ceramic filler is used and it is even better when surface modified ceramic particles are used.

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