The Formation and Structure of Vulcanizates

1949 ◽  
Vol 22 (1) ◽  
pp. 96-104
Author(s):  
J. Bardwell ◽  
C. A. Winkler
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Physical Properties ◽  
Network Structure ◽  
Weight Distribution ◽  
Elastic Behavior ◽  
Cross Linking ◽  
Structural Factors ◽  
Experimental Proof ◽  
Vulcanized Rubber

Abstract The characteristic mechanical properties of vulcanized rubber are believed to result from a network structure made up of chainlike molecules bonded together by occasional cross-linkages. In relating the physical properties of the vulcanizate to the structure of the network, it is therefore necessary to consider the concentration of cross-linkages and the molecular-weight distribution of the rubber molecules before cross-linking. Various theories have been proposed for the dependence of elastic properties on these structural factors, but experimental proof of the suggested relations has been meager, largely because of the complexities met with in, vulcanization reactions. In the present investigation some of these difficulties have been overcome, and the quantitative relations between the elastic behavior of GR-S and its network structure have thereby been revealed.

Effect of molecular weight distribution on the rheological and mechanical properties of polypropylene

1989 ◽  
Vol 29 (6) ◽  
pp. 390-396 ◽  
Author(s):  
C. Tzoganakis ◽  
J. Vlachopoulos ◽  
A. E. Hamielec ◽  
D. M. Shinozaki
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution

Novel Polyaspartic Ester Polyureas Based on Flexible Polyaspartic Ester

2011 ◽  
Vol 197-198 ◽  
pp. 1294-1298
Author(s):  
Ping Lu ◽  
Wei Bo Huang ◽  
Xue Qiang Ma ◽  
Xu Dong Liu
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Hydrogen Bonding ◽  
Molecular Weight Distribution ◽  
Michael Addition ◽  
Weight Distribution ◽  
Addition Reaction ◽  
Chain Extender ◽  
Michael Addition Reaction ◽  
Ft Ir

New polyaspartic ester (PAE) chain extender named PAE-f was prepared via two steps of Michael addition reactions:(1) Michael addition reaction between 4,4’-methylenebis(2-methyl cyclohexyl amine) (Laromin C260) and excessive dialkyl maleates（DEF）; (2) The Michael addition reaction of the residual dialkyl maleates of step (1) with polyester polyamine Jeffamine D230. The two-steps method proposed could reduce the reaction time in comparison with the current one step Michael addition reaction method, thus satisfying the industrialized production. New PAE based polyureas were synthesized by reacting the PAE-f chain extender with aliphatic polyisocyanates 4,4’-diisocyanato dicyclohexylmethane (H12MDI) / polyester polyamine Jeffamine D2000 prepolymer at room temperature. FT-IR and GPC were employed to characterize the new PAE prepared, and the morphology, molecular weight distribution and mechanical properties of the prepared PAE based polyureas were investigated by means of FT-IR and GPC. The FT-IR results indicated that the hydrogen bonding degree of amidogen groups in hard segments of the prepared polyureas were high, the length of hydrogen bonding were 0.305nm～0.306nm. The GPC experimental results show that the weight average molecular weight of the PAE-f based polyureas were 4.95×104～6.05×104,Mw/Mn were 1.65～1.97, the molecular weight distribution were relatively narrow. The mechanical properties demonstrated that the tensile strength were 14.7～22.5MPa, Elongation at break were 306～511%, Yang’s modulus were 67～127MPa, Shore A hardness were 64～83. The mechanical properties confirmed that the polyureas based on PAE-f were kinds of elastomeric materials with satisfied flexibility, strength, module and hardness.

PEG Cross-Linked Alginate Hydrogels with Controlled Mechanical Properties

1998 ◽  
Vol 530 ◽  
Author(s):  
Petra Eiselt ◽  
Jon A. Rowley ◽  
David J. Mooney
Keyword(s):  
Mechanical Properties ◽  
Tissue Engineering ◽  
Molecular Weight ◽  
Elastic Modulus ◽  
Cell Transplantation ◽  
Cross Linking ◽  
Cross Link ◽  
Link Density ◽  
A Cell ◽  
Cross Link Density

AbstractReconstruction of tissues and organs utilizing cell transplantation offers an attractive approach for the treatment of patients suffering from organ failure or loss. Highly porous synthetic materials are often used to mimic the function of the extracellular matrix (ECM) in tissue engineering, and serve as a cell delivery vehicle for the formation of tissues in vivo. Alginate, a linear copolysaccharide composed of D-mannuronic acid (M) and L-guluronic acid (G) units is widely used as a cell transplantation matrix. Alginate is considered to be biocompatible, and hydrogels are formed in the presence of divalent cations such as Ca2+, Ba2+ and Sr2+. However, ionically cross-linked alginate gels continuously lose their mechanical properties over time with uncontrollable degradation behavior. We have modified alginate via covalent coupling of cross-linking molecules to expand and stabilize the mechanical property ranges of these gels. Several diamino PEG molecules of varying molecular weight (200, 400, 1000, 3400) were synthesized utilizing carbodiimide chemistry. Sodium alginate was covalently cross-linked with these cross-linking molecules, and mechanical properties of the resulting hydrogels were determined. The elastic modulus of the cross-linked alginates depended on the molecular weight of the cross-linking molecules, and ranged from 10-110 kPa. The theoretical cross-link density in the hydrogels was also varied from 3 to 47% (relative to the carboxylic groups in the alginate) and the mechanical properties were measured. The elastic modulus increased gradually and reached a maximum at a cross-link density of 15%. In summary, covalently coupled hydrogels can be synthesized which exhibit a wide range of mechanical properties, and these materials may be useful in a number of tissue engineering applications.

Fractionation of Polymers

1972 ◽  
Vol 45 (3) ◽  
pp. 667-708 ◽  
Author(s):  
W. V. Smith
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Structural Information ◽  
Gel Permeation Chromatography ◽  
Molecular Weight Distributions ◽  
Polymer Solubility ◽  
Homogeneous Composition ◽  
Layer Chromatography

Abstract Fractionation is an important tool for obtaining structural information on polymers. It is also important for isolating relatively homogeneous samples of polymer to use in determining relationships between structure and properties. The most common structural information obtained from fractionation is molecular weight distribution (MWD). This is a very important factor in determining processing behavior. To a lesser extent MWD affects the properties of finished polymer products. It is quite important in helping to elucidate mechanisms of polymer formation. Development of gel permeation chromatography (GPC) over the past few years has provided a fast convenient tool for comparing molecular weight distributions. GPC is fast enough that it may even be considered as a potential means of controlling polymerization processes. The chemical composition of copolymers can be determined using fractionation techniques. For this the fractionations based on polymer solubility are particularly suitable. Thin layer chromatography also shows promise in this area. This information is of importance in respect to some physical properties such as solvent and oil resistance and crystallinity. It is also useful in elucidating mechanisms of polymerization. While the ultracentrifuge has not been used extensively in the investigation of industrial polymers, it does have the advantage of being capable of providing absolute moleclar weight information. When it is desired to establish relationships between the structure of polymers and their physical properties it is always desirable to work with polymers having a narrow molecular weight distribution and a homogeneous composition. This can frequently best be accomplished by using fractionated polymer samples. At the present time fractionations based on solubility are the principal ones used through preparative fractionations based on GPC are now possible and a limited amount of literature in this area is now appearing.

Characteristic Properties of Rubber at Low Temperatures. A Discussion of the Stress-Strain Curves of Vulcanized Rubber at Low Temperatures

1934 ◽  
Vol 7 (4) ◽  
pp. 610-617 ◽  
Author(s):  
Takeo Fujiwara ◽  
Toramatsu Tanaka
Keyword(s):  
Physical Properties ◽  
Low Temperatures ◽  
External Heat ◽  
Point Of View ◽  
Special Importance ◽  
Stress Strain ◽  
Experimental Proof ◽  
Vulcanized Rubber ◽  
The Subject ◽  
Two Phases

Abstract The hardening of rubber at low temperatures is one of the well-known physical characteristics of rubber. The loss of elasticity of raw rubber by hardening at 0° to 10° C., its turning to the consistency of glass, and its fragility at −19° C. when cooled with liquid air, and its fibering when stretched to 60–70 per cent previous to breaking, give an experimental proof of the theory of the structure of rubber molecules. Vulcanization makes raw rubber physically less sensitive to heat and to low temperatures, and is of great significance, because it enables vulcanized rubber to be used around −30° C. without losing its elasticity. The effect of external heat on the physical properties, especially on the stress-strain relations, of vulcanized rubber has been discussed mainly for temperatures from −10° to +100° C., and only two papers deal with temperatures from −30° to −60° or −70° C. (cf. Le Blanc and Kröger, Kolloid Z., 37, 205 (1925); Tener, Kingsbury and Holt, Bureau of Standards Technologic Papers Vol. 22, No. 364). Of special importance are a means of recognizing changes m the physical properties (phenomenon of freezing-hard ness) of vulcanized rubber at −30° to −60° or −70° C., and the practical value of such information. Though there is a contradiction in the fundamental meaning of the “cold resistant theory” of rubber, investigations of the two phases of the subject may throw some light on practical problems and widen the scientific point of view.

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