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.

Improved Deproteinization Process for Protein-Free Natural Rubber Latex

2013 ◽  
Vol 844 ◽  
pp. 474-477 ◽  
Author(s):  
Wiwat Pichayakorn ◽  
Jirapornchai Suksaeree ◽  
Wirach Taweepreda
Keyword(s):  
Natural Rubber ◽  
Negative Charge ◽  
Ph Value ◽  
Natural Rubber Latex ◽  
Solid Content ◽  
Enzyme Treatment ◽  
Distilled Water ◽  
Rubber Latex ◽  
Total Solid Content ◽  
Leaching Process

Hev b1-14 type proteins in natural rubber latex (NRL) have been identified as allergens in immunogenic responses. Several methods have been developed to reduce these proteins from NRL such as enzyme treatment, centrifugation, creaming, simple or ultrasonic leaching, and chlorination. In this work, the improvement of deproteinization of NRL was developed using the combination of enzyme treatment and leaching processes. The fresh NRL was incubated with 0.2 phr proteolytic alcalase enzyme, and preserved with 2%v/v paraben concentrate in the presence of a 2%v/v sodium lauryl ether sulfate (SLES) as a surfactant at 37°C for 24 hours, and then centrifuged. The upper rubber mass was then leached for three times with either distilled water, a 1%v/v SLES solution, or a mixture of 1%v/v SLES and 2.5%v/v ethanol, and then finally re-dispersed in distilled water. It was found that the increasing process of leaching with either 1%v/v SLES or a mixture of 1%v/v SLES and 2.5%v/v ethanol had the higher efficacy to reduce the remained protein in deproteinized NRL (DNRL). The best deproteinized process was the enzyme treatment and followed by the three times leaching process with a mixture of 1%v/v SLES and 2.5%v/v ethanol, that could completely reduce the proteins in DNRL to 0%. This DNRL had the pH value, viscosity, dry rubber content, and total solid content of 7.41, 13.82 cps, 42.57%, and 44.63%, respectively. Its particle size was 626.23 nm with low polydispersity index of 0.16. The negative charge of SLES could increase the higher negative charge of DNRL to-63.20 mV that exhibited very good physical stability during storage. In conclusions, the combination of enzyme treatment and leaching process with both SLES and ethanol was successful to produce the protein-free DNRL. This DNRL could be further used for several applications including medical skin products.

Effect of Modified Natural Rubber on Morphology, Chemical Structure, and Crystallinity of Electrospun Polyvinylidene Difluoride Nanofibers

2019 ◽  
Vol 950 ◽  
pp. 128-132
Author(s):  
Jean Raynell S. Bello ◽  
Bryan B. Pajarito ◽  
Jem Valerie D. Perez
Keyword(s):  
Natural Rubber ◽  
Chemical Structure ◽  
Fiber Diameter ◽  
Natural Rubber Latex ◽  
X Ray Diffraction ◽  
Rubber Latex ◽  
Polyvinylidene Difluoride ◽  
X Ray ◽  
Chemically Modified ◽  
Enzymatic Deproteinization

Natural rubber latex was chemically modified by enzymatic deproteinization, degradation, and epoxidation to produce deproteinized liquid epoxidized natural rubber (DP-LENR). Polyvinylidene difluoride (PVDF) was blended with DP-LENR and then electrospun to produce nanofibers. Scanning electron microscopy shows reduction in the fiber diameter and beading formation with increasing concentration of DP-LENR. Smooth surface of nanofibers suggests miscibility and chemical compatibility of PVDF with low concentration of DP-LENR. Infrared spectroscopy and X-ray diffraction analysis show the addition of DP-LENR has no effect on chemical structure and crystallinity of electrospun PVDF.

An Optimization Study on the Inclusion of Aluminium Hydroxide into Natural Rubber Latex as Deproteinization Agent

2013 ◽  
Vol 844 ◽  
pp. 399-405
Author(s):  
Lim Keuw Keuw Wei ◽  
Khairiah Haji Badri ◽  
Wong Chong Ban
Keyword(s):  
Fourier Transform ◽  
Natural Rubber ◽  
Protein Content ◽  
Functional Group ◽  
Ph Value ◽  
Natural Rubber Latex ◽  
Rubber Latex ◽  
Optimum Amount ◽  
Optimization Study ◽  
Preliminary Study

A preliminary study was conducted to investigate the effect of aluminum hydroxide (ATH) as a deproteinizing agent in commercial natural rubber latex (NRL) onto the physicochemical properties of the NRL. The loading of ATH in NRL was varied at 0.05 parts per hundred rubbers (phr), 0.10 phr, 0.15 phr and 0.20 phr. The optimum amount of ATH in NRL was determined from pH value, mechanical strength time (MST), protein content and Fourier Transform Infrared spectroscopy. The addition of ATH in NRL reduced the protein content of NRL (3.52%) to the lowest (1.19%) at 0.15 phr ATH. Protein-aluminate complex was detected from the FTIR spectra through peak at 3498 cm-1, referred to as C-N-H functional group.

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.

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.

Novel Process in Preparation of Deproteinized Natural Rubber Latex

2013 ◽  
Vol 844 ◽  
pp. 462-465 ◽  
Author(s):  
Prapaporn Boonme ◽  
Wirach Taweepreda ◽  
Wiwat Pichayakorn
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Ph Value ◽  
Skin Irritation ◽  
Natural Rubber Latex ◽  
Pharmaceutical Formulations ◽  
Solid Content ◽  
Rubber Latex ◽  
Total Solid Content ◽  
Deproteinized Natural Rubber

Natural rubber latex (NRL) tapped from Hevea brasiliensis is composed of cis-1,4-polyisoprene as the major polymer which provides several desirable physical properties which make it to be interesting in pharmaceutical formulations. However, the International Union of Immunological Societies (IUIS) has reported about latex allergies caused by 14 NRL proteins (Hev b1-14). This problem can be coped with deproteinization of NRL in order to obtain deproteinized natural rubber latex (DNRL). This study aimed to prepare DNRL by novel process which was easy to perform and used pharmaceutical acceptable agents. The obtained DNRL was assayed for remained protein amount in form of nitrogen content by Kjeldahl method. Its physical properties were characterized. Its stability was also physically investigated. The DNRL was tested for the skin irritation in 3 rabbits. It was found that the protein amount of DNRL was 0.257% while the initial protein amount of fresh NRL was 1.531%. Hence, the protein was removed for 83.21%. DNRL had the average pH of 7.27. Both protein content and pH value implied that DNRL should be safe for skin application. DNRL possessed Newtonian flow with low viscosity which should be easy for mixing with other components in the further pharmaceutical formulations. The particle size, polydispersity index (PI), and zeta potential of DNRL were 441.0 nm, 0.240, and -42.53 mV, respectively, indicating narrow size distribution and physical stability. The dry rubber content and total solid content of DNRL were controlled as 39.55% and 40.72%, respectively. The suitable storage condition of DNRL was at 2-8°C in tight containers where DNRL could be kept for longer than 4 months. Very slightly irritation with no allergy caused by DNRL was observed in the tested rabbits. It could be concluded that this deproteinization process was easy and the prepared DNRL by this process was suitable and safe for using in further pharmaceutical and cosmetic formulations.

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