Gel Formation in Natural Rubber Latex: 2. Effect of Magnesium Ion

2003 ◽  
Vol 76 (5) ◽  
pp. 1185-1193 ◽  
Author(s):  
L. Tarachiwin ◽  
J. T. Sakdapipanich ◽  
Y. Tanaka
Keyword(s):  
Natural Rubber ◽  
Natural Rubber Latex ◽  
Storage Period ◽  
Gel Formation ◽  
Gel Content ◽  
Gel Fraction ◽  
Rate Of Increase ◽  
2So4 Concentration ◽  
Gel Phase ◽  
Long Storage

Abstract The effect of Mg2+ ions on the gel formation in fresh and commercial high ammonia natural rubber latices (FL-latex and commercial HA-latex) was analyzed from the gel content and 2+ content after treatment with (NH4)2SO4. The gel content of rubber from commercial HA-latex decreased significantly after (NH4)2SO4 treatment comparable to that of FL-latex. Long-storage commercial HA-latex containing 50% gel fraction showed no decrease in 2+ content after (NH4)2SO4 treatment. This gel fraction was not solubilized in toluene by the treatment of a proteolytic enzyme in latex or ethanol/toluene mixed solvent extraction of rubber. The 2+ content of rubber in long-storage commercial HA-latex, 0.005% (w/w rubber), decreased after treatment with (NH4)2SO4, while the same treatment showed little change on FL-latex, 0.035%. The toluene soluble fraction of these latices showed a decrease in the Mn value with an increase in the (NH4)2SO4 concentration. The gel content of FL- and HA-lattices increased with an increasing storage period in the presence and absence of (NH4)2SO4. The initial rate of increase in the gel content was slow in the case of FL-latex. These findings indicate that the gel fraction in HA-latex is partly formed by ionic crosslinks caused by 2+ ions. Whereas, the gel phase in long-storage commercial HA-latex is presumed to be a hard gel predominantly formed by covalent bonding.

Gel Formation in Natural Rubber Latex: 1. Effect of (NH4)2HPO4 and TMTD/ZnO Additives

2003 ◽  
Vol 76 (5) ◽  
pp. 1177-1184 ◽  
Author(s):  
L. Tarachiwin ◽  
J. T. Sakdapipanich ◽  
Y. Tanaka
Keyword(s):  
Natural Rubber Latex ◽  
Gel Formation ◽  
Rubber Latex ◽  
Tetramethylthiuram Disulfide ◽  
Gel Content ◽  
Gel Fraction ◽  
Initial Stage ◽  
High Ammonia ◽  
Long Time ◽  
Long Storage

Abstract The rubber from commercially obtained high-ammonia latex (commercial HA-latex) increased in gel content significantly after long preservation of the latex with 1.0% w/v tetramethylthiuram disulfide (TMTD) and zinc oxide (ZnO). Deproteinization of the HA-latex did not decrease the gel content. The gel fraction of deproteinized commercial HA-latex (DPHA-latex) was not solubilized by toluene containing 1.0% ethanol, showing that the gel fraction is composed of chemically crosslinked rubber. The addition of (NH4)2HPO4, which is usually added to fresh latex (FL-latex) to remove excess amounts of Mg2+ ions by centrifugation, decreased the gel formation in FL-latex preserved with 0.6 % v/v NH4OH due to the removal of Mg2+ ions. The excess amounts of (NH4)2HPO4 accelerated the gel formation in preserved FL-latex and commercial HA-latex. The addition of 0.1% w/v TMTD/ZnO to preserved FL-latex treated with 5% w/v (NH4)2HPO4 caused an increase of gel content during storage. The gel formation in the commercial HA-latex during long time storage was presumed to be caused by excess amounts of Mg2+ ions, TMTD/ZnO and (NH4)2HPO4. Here, TMTD/ZnO accelerated the gel formation at the initial stage of storage, while (NH4)2HPO4 affected in long storage.

Rheological Behavior Characterization of Natural Rubber Containing Different Gel

2014 ◽  
Vol 970 ◽  
pp. 320-323 ◽  
Author(s):  
Saengchao Thongseenuch ◽  
Wirach Taweepreda ◽  
Krisda Suchiva
Keyword(s):  
Molecular Structure ◽  
Natural Rubber ◽  
Rheological Behavior ◽  
Loss Modulus ◽  
Natural Rubber Latex ◽  
Gel Structure ◽  
Gel Content ◽  
Molecular Weights ◽  
Branching Points

This research, natural rubber containing different gel contents were prepared by deproteinization and saponification treatment from high ammonium natural rubber latex. Deproteinization natural rubber was further treated as acetone extraction and then transesterification. It was founded that gel content and molecular weights of treated natural rubber were decreased and almost absented for transesterification treatment. Rheological respond on small amplitude oscillating shear (SAOS) and large amplitude oscillating shear (LAOS) deformation of treated natural rubber were captured by using rubber process analyzer (RPA 2000). Firs harmonic rheological properties, storage modulus, G and loss modulus, G decreased as gel content and molecular weight decreased. It was believed that gels, explicitly branching points, were destroyed after the natural rubber was deproteinized, transesterification, or saponification according to the molecular structure of natural rubber presumed by Tanaka et al, which functional groups contain protein and fatty acid are participated in branching to forming gel structure. It was concluded that gel content as the same as molecular structure of natural rubber could be characterized as rheological behavior.

A Vibrational Spectroscopic Analysis of the Structure of Natural Rubber

1987 ◽  
Vol 60 (4) ◽  
pp. 647-658 ◽  
Author(s):  
F. J. Lu ◽  
S. L. Hsu
Keyword(s):  
Natural Rubber ◽  
Functional Groups ◽  
Spectroscopic Analysis ◽  
Extraction Solvent ◽  
Gel Fraction ◽  
Gel Phase ◽  
Composition Structure ◽  
Vulcanization Process ◽  
Structural Aspects ◽  
Soluble Part

Abstract It is not an overstatement to say that natural rubber (NR) is one of the most used polymers. There are numerous studies dealing with the structural aspects of rubber which give rise to its elastic property. However, it should be emphasized that the majority of these studies are generally concerned with rubber in the vulcanized state or, in fact, dealing with the vulcanization process. Relatively few studies have actually been directed at a better understanding of the composition, structure, and properties of raw rubber. This area of study is also important because the composition and the structure of NR differ from synthetic polyisoprene in that the presence of functional groups on main chains and nonrubbery materials, such as proteins, can significantly affect the rheological properties and the processing conditions of rubber before the vulcanization process. Raw rubber can be divided into two different fractions, sol (soluble part) and gel (insoluble part). Of course, this definition depends somewhat on the solvent used. Even though the main chain in both portions of rubber are chemically similar, their significantly distinct mechanical properties have, in fact, been attributed to the nonrubbery materials such as proteins interacting with isoprene chains. It is generally accepted that the amount of nonrubbery materials in the gel fraction is much higher than the sol fraction. The protein apparently interacts quite strongly with specific functional groups on the isoprene chain and is difficult to remove from the gel phase by physical means. It is probable that the different properties between sol and gel rubber is due to the amount of crosslinking of the main chains, but several aspects of the structure need to be answered in greater detail. We know, for example, that the amount of gel fraction can change as a function of extraction solvent. Therefore, one cannot conclude that the interaction between rubber chains even in the gel fraction is strictly chemical in nature. Our premise is that the protein is an important component connecting the isoprene chains.

EFFECT OF DECELERATED FERMENTATION ON MORPHOLOGY AND MECHANICAL PROPERTIES OF NATURAL RUBBER LATEX

2013 ◽  
Vol 86 (4) ◽  
pp. 615-625 ◽  
Author(s):  
Oraphin Chaikumpollert ◽  
Osamu Wakisaka ◽  
Akio Mase ◽  
Yoshimasa Yamamoto ◽  
Krisda Suchiva ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Scanning Probe Microscopy ◽  
Natural Rubber Latex ◽  
Rubber Latex ◽  
Gel Content ◽  
High Ammonia ◽  
The Relationship ◽  
Nanomatrix Structure ◽  
Morphology And Mechanical Properties

ABSTRACT Decelerated fermentation of natural rubber latex was performed to investigate the relationship between the morphology and mechanical properties of natural rubber. Natural rubber latex was preserved with sodium hydroxymethylglycinate, as a bactericide, to decelerate the fermentation of nonrubber components such as proteins, phospholipids, carbohydrate, and so forth. Gradual increases in the viscosity of the latex and gel content of the resulting rubber took place as the preservation period was prolonged, which were distinguished from less change in the viscosity of high-ammonia natural rubber (HANR) and high gel content of its rubber. The particle size distribution was dramatically changed during decelerated fermentation, although that of the HANR latex did not change. The pH and nitrogen content of the rubbers were independent of the preservation time. Morphology of the fermented natural rubber and the HANR was observed with scanning probe microscopy. Fewer mechanical properties of the fermented natural rubber were related to the destruction of the nanomatrix structure of the nonrubber components, which resulted from the decrease in the fatty acid ester groups with bacteria as compared with the good mechanical properties of the HANR.

Effect of Non-Rubber Components on Storage Hardening and Gel Formation of Natural Rubber During Accelerated Storage under Various Conditions

2003 ◽  
Vol 76 (5) ◽  
pp. 1228-1240 ◽  
Author(s):  
Jintana Yunyongwattanakorn ◽  
Yasuyuki Tanaka ◽  
Seiichi Kawahara ◽  
Warunee Klinklai ◽  
Jitladda Sakdapipanich
Keyword(s):  
Natural Rubber ◽  
Ph Value ◽  
Natural Rubber Latex ◽  
Long Chain Fatty Acid ◽  
Gel Fraction ◽  
Constant Ph ◽  
Accelerated Storage ◽  
Low Humidity ◽  
Enzymatic Deproteinization ◽  
Clear Increase

Abstract The phenomenon of storage hardening in solid natural rubber (NR) is presumed to occur by means of reactions between some non-rubber components and abnormal groups in rubber molecule. The main non-rubber constituents in NR are composed of proteins and lipids. The storage hardening behavior of NR purified by enzymatic deproteinization and transesterification was analyzed under high and low humidity conditions using phosphorus pentoxide (P2O5) and sodium hydroxide (NaOH). The NR obtained from centrifuged fresh natural rubber latex (CFNR) and deproteinized NR latex (DPNR) showed significant increase in the hardening plasticity index (PH) value during storage; while that of the transesterified NR (TENR) and transesterified DPNR (DPTE-NR) was almost constant during storage. After keeping samples under high humidity conditions, the fresh natural rubber (FNR), CFNR and DPNR showed constant PH value, while that of the TENR and DPTE-NR decreased during storage. The FNR, CFNR and DPNR showed a clear increase in the gel fraction after the occurrence of storage hardening reaction. The gel fraction showed molecular weight between crosslinks (Mc) of about 104. Glass transition temperature (Tg) of gel fraction was higher than that observed in the case of sol fraction. The formation of crosslinking and branching during accelerated storage was presumed to be due to the chemical bonding between the active functional groups in the long-chain fatty acid of phospholipids at the terminating end of rubber molecules under low humidity conditions.

The Gel Phase in Natural Rubber

1963 ◽  
Vol 36 (4) ◽  
pp. 1024-1034 ◽  
Author(s):  
P. W. Allen ◽  
G. M. Bristow
Keyword(s):  
Electron Microscopy ◽  
Light Scattering ◽  
Natural Rubber ◽  
Diffusion Rate ◽  
Latex Particles ◽  
Gel Content ◽  
Soluble Component ◽  
Microgel Particles ◽  
The Matrix ◽  
Gel Phase

Abstract Evidence is presented which suggests that the true gel phase in natural rubber is composed of small crosslinked latex particles (microgel), whose presence is revealed by light scattering and by electron microscopy. These are combined into a matrix with soluble rubber molecules, forming the apparent gel phase. The rate of solution (and hence the apparent gel content) of this phase varies with solvent and is governed by the diffusion rate of solvent into rubber. Prolonged extraction removes the soluble component. Since the redissolution of the soluble component is very rapid, it is inferred that it is initially bound to the microgel particles by specific forces which have to be overcome by the diffusing solvent. Mastication of crepe breaks up the matrix, leaving microgel particles whose presence can be detected in solution.

Role of Gel Content on the Structural Changes of Masticated Natural Rubber

2013 ◽  
Vol 844 ◽  
pp. 101-104 ◽  
Author(s):  
Adun Nimpaiboon ◽  
Sureerut Amnuaypornsri ◽  
Jitladda Sakdapipanich
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Shear Force ◽  
Structural Changes ◽  
Gel Content ◽  
Gel Fraction ◽  
Accelerated Storage ◽  
Strain Sweep ◽  
Mooney Viscosity

In this study, natural rubber (NR) containing various amounts of gel was prepared by accelerated storage hardening to investigate the role of gel content on the structural changes of masticated NR. The NR samples containing various amounts of gel were subjected to mastication at various times, and subsequently characterized for the change of gel content, molecular weight, and Mooney viscosity to evaluate the role of gel content on these parameters. Furthermore, an oscillatory shear experiment using a strain sweep test was applied in this study to elucidate the structural changes of rubber samples after mastication. The results revealed that the Mooney viscosity was related to the percentage of gel fraction that has been proven to be the result of the interactions of proteins and phospholipids at the chain ends. The gel fraction of NR can be decomposed into a sol fraction by shear force during mastication and the mastication time for decomposition of gel relates to the initial gel content of the rubber. After mastication for 15 min, although the gel fraction of NR can be decomposed to ~0% w/w, the interactions of proteins and phospholipids at the chain ends still existed, and their quantities is corresponded to the gel content of raw rubber.

Morphology and Crystallization Behavior of Lightly Crosslinked Natural Rubber in Blend

2003 ◽  
Vol 76 (5) ◽  
pp. 1164-1176 ◽  
Author(s):  
Tetsuji Kawazura ◽  
Seiichi Kawahara ◽  
Yoshinobu Isono
Keyword(s):  
Natural Rubber ◽  
Homogeneous Nucleation ◽  
Crosslink Density ◽  
Model Compound ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Gel Content ◽  
Gel Fraction ◽  
Compound Model ◽  
Styrene Butadiene

Abstract Isothermal crystallization of natural rubber (NR) dispersed in styrene-butadiene rubber (SBR) was made at −25 °C to investigate effects of both gel fraction of the rubber and morphology of the blend on the crystallization. NR, thus used, was lightly crosslinked model compound (model-NR), which was cured with dicumylperoxide at 160 °C after mastication. The model-NR was mechanically mixed with a large amount of SBR to form droplets of the rubber, a size of which was dependent upon both gel content and crosslink density of the gel fraction. The crystallization of the model-NR in the droplets was quite slow, corresponding to the level reported in the previous work. A rate of crystallization and Avrami exponent were dependent upon the size of the droplets, but not on the gel content and the crosslink density of the model-NR. The suppression in the crystallization was attributed to the homogeneous nucleation occurring in the droplets. This finding was proved, using rubbers obtained from two clones of Hevea brasiliensis, i.e. RRIM600 and RRIM2025, respectively.

scholarly journals Effect of Stabilizer States (Solid Vs Liquid) on Properties of Stabilized Natural Rubbers

Polymers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 741 ◽  
Author(s):  
Khwanchat Promhuad ◽  
Wirasak Smitthipong
Keyword(s):  
Natural Rubber ◽  
Liquid State ◽  
Room Temperature ◽  
Gel Formation ◽  
Rubber Industry ◽  
Gel Content ◽  
Mooney Viscosity ◽  
Mixing States ◽  
Hydroxylamine Sulfate ◽  
Stabilizer States

The main objective of this work is to study the effect of hydroxylamine sulfate or stabilizer states (solid vs liquid) on the storage hardening of natural rubber (NR). Several types of natural rubber samples were prepared: unstabilized NR samples and stabilized NR samples: (i) dry NR with 0.2 and 2.0 parts per hundred rubber (phr) of dry hydroxylamine sulfate, and (ii) natural latex with 0.2 and 2.0 phr of liquid hydroxylamine sulfate. The samples were characterized immediately (time 0) and after 12 weeks of storage at room temperature, respectively. We found that the Mooney viscosity, gel content, and Wallace plasticity of NR without a stabilizer increases with storage hardening for 12 weeks. However, two types of stabilized NR samples represent constant values of those three parameters, because hydroxylamine sulfate inhibits network and gel formation in NR. Interestingly, the mixing states (solid vs liquid) between natural rubber and the stabilizer affect the properties of stabilized NR. This could be explained by the better dispersion and homogeneous nature of liquid stabilizers in natural latex (liquid state), and thus the higher loading of the stabilizer in the liquid state. This is important, as the stabilization of NR properties as a function of time is required by rubber industry. This study is a utilization model from theory to application.

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