Characterization of the Large and Small Rubber Particles in Fresh Hevea Latex

2002 ◽  
Vol 75 (2) ◽  
pp. 179-185 ◽  
Author(s):  
Jitladda T. Sakdapipanich ◽  
Kanjanee Nawamawat ◽  
Seiichi Kawahara
Keyword(s):  
Molecular Weight ◽  
Particle Size ◽  
Physical Properties ◽  
Weight Distribution ◽  
Rubber Latex ◽  
Mature Trees ◽  
Branching Points ◽  
Rubber Particles ◽  
Linear Molecules

Abstract The rubbers from small and large rubber particles were separated from the serum and cream phases of centrifuged fresh Hevea latex, respectively. The small rubber particles (SRP) consist of rubber molecules showing a unimodal molecular weight distribution (MWD), with a peak-top value falling between the two peak values of the bimodal MWD observed in rubbers from the large rubber particles (LRP). The rubbers in LRP from mature trees and SRP from seedlings are polyisoprene molecules terminated by phospholipids comprising branching points, while those in SRP from mature trees are presumed to be linear molecules containing no phospholipid terminal. The serum rubber was found to be soft and viscous rubber differing from the cream rubber containing in LRP. Thus, it can be presumed that the particle size of rubber latex is an important parameter influencing the MW, MWD and physical properties of Hevea rubber.

Characterization of Polymers by GPC-LALLS. III. Branching Structure of EPDM

1987 ◽  
Vol 60 (1) ◽  
pp. 1-13 ◽  
Author(s):  
S. Shiga ◽  
Y. Sato
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Gamma Ray ◽  
B Value ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Branching Points ◽  
Aluminum Halide ◽  
Linear Molecules

Abstract Gamma ray-irradiated EPM's, as the model polymers of branched EPDM, are investigated using the relationship g′=gb, where g′ is the ratio of intrinsic viscosities of the branched and the linear molecules of equal molecular weight, [η]br/[η]l, and g, the ratio of the mean square radii of gyration of the two, 〈s2〉br/〈s2〉l. The molecular weight distributions measured by GPC-LALLS coincide well with theoretical curves of tetrafunctionally and statistically branched polymers obtained by the ideal degradation and crosslinking of the raw EPM, which was assumed to have the most probable molecular weight distribution, and the b-value is then determined to be 1.1. EPDM samples, polymerized with a soluble vanadium compound—alkyl aluminum halide type catalyst in a continuous well-stirred pilot-reactor, are characterizedas to the number of branching points per molecule for various molecular weights by using the b-value. The higher the molecular weight, the smaller the distance between neighboring crosslinking points. The reason is discussed. The unsaturated bond of dicyclopentadiene crosslinks more readily in the manufacturing process than 5-ethylidene-2-norbornene. The largest high molecular weight portion and the broadest molecular weight distribution are observed in the EPDM with the maximum dicyclopentadiene content.

A Progress in Development and Application of Size Exclusion Chromatograph/Multi-Angle Laser Light Scattering

2014 ◽  
Vol 936 ◽  
pp. 1597-1602
Author(s):  
Xue Yang ◽  
Ze Quan Liu ◽  
Qiang Zhang
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Laser Light ◽  
Laser Light Scattering ◽  
Size Exclusion

This paper reveals the development and significance of size exclusion chromatograph/multi-angle laser light scattering(SEC-MALLS) for determination of the molecular weight and characterization of the molecular weight distribution. This technque has been applied in many aspects, such as biology, polymer and carboxylate surfactant. It has made a big contribution to study the property of macromolecular substances.

Characterization of Sol and Gel in Hevea Natural Rubber

1997 ◽  
Vol 70 (5) ◽  
pp. 707-713 ◽  
Author(s):  
Jitladda Tangpakdee ◽  
Yasukuki Tanaka
Keyword(s):  
Molecular Weight ◽  
Weight Fraction ◽  
Toluene Solution ◽  
Low Molecular Weight ◽  
Branch Points ◽  
Gel Content ◽  
High Ammonia ◽  
Linear Molecules ◽  
Cis And Trans

Abstract The gel content of rubber from high-ammonia latex (HA-latex) decreased significantly after deproteinization with proteolytic enzyme. The addition of 1–2% ethanol in toluene solution reduced the gel content of rubbers from HA-latex, deproteinized HA-latex (HA-DP) and pale crepe. Transesterification of the rubber in toluene solution with sodium methoxide dissolved the gel fraction. The gel fractions solubilized after transesterification showed molecular weight distribution rich in low molecular-weight fraction. The Huggins k′ constant of the fractionated rubbers from solubilized-gels was in the range of 0.42–0.45, lower than that of the fractionated HA-DP of 0.5–0.8. This indicates that all the branch-points were decomposed by transesterification to form linear molecules. The Mn values of rubber chains assembling the gel was 5.5−8.3×105 by 13C-NMR measurements of the ratio between cis- and trans-isoprene units, which were comparable to the molecular weight between crosslinks, Mc, of 7−11×105 by swelling measurements. These findings suggest that the branching and crosslinks are composed of two types of branch-points, i. e. one by association or aggregation of proteins or oligopeptides at the initiating end and the other by ester linkages including phosphoric ester at the terminal end.

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