Control of the degradation of natural rubber : analysis and application of naturally occurring anti-and pro-oxidants in natural rubber

การควบคุมการย่อยสลายของยางธรรมชาติ : การวิเคราะห์และการประยุกต์ใช้สารต้านและสารเร่งการเกิดออกซิเดชันที่มีอยู่ในยางธรรมชาติ

Name: Surakit Tuampoemsab

LCSH: Rubber

LCSH: Rubber -- Thermal properties

Abstract: Natural rubber (NR) generally disintegrates by oxidative degradation on the polyisoprene chain, leading to a dramatic loss in physical properties both in the raw and vulcanized forms. Thus, the role of naturally occurring anti- and pro-oxidants in the thermal oxidative degradation of NR was investigated, especially for lipids and proteins. Accelerated heat aging test at 100
C was carried out for purified NR and synthetic polyisoprene as well as their recombination with the natural extracts. Deteriorations of the uncured rubber such as molecular weight, green strength and Wallace plasticity were elucidated. Deproteinized NR (DPNR) re-added with the extractable lipids was the most sensitive for oxidative degradation. Proteins derived from fresh latex NR (FLNR) and lipids-removed NR (LRNR) exhibited as one of the natural antioxidants to hinder the activity of alkylperoxyl radicals, possibly generated from the free fatty acids, under heat accelerated condition. The lipids isolated from the fresh NR latex contained many types of free fatty acid and fatty acid ester. Heat-aging properties of the rubber vulcanized by sulfur and peroxide systems were also studied. In the case of rubber cured by sulfur system, the proteins and lipids have been presented as accelerators and accelerated activators, respectively. Peroxide-vulcanized rubber, however, exhibited aging behaviors similar to the uncured sample. Extensibility graph plotted between log b and log M100 of the vulcanizate was achieved to analyze the aging properties. Finally, antagonism between fatty acid and amino acid was studied for both sulfur and peroxide vulcanizates. Auto-oxidation mechanism of saturated and unsaturated fatty acids, accelerating the oxidative degradation of polyisoprene rubber, was discussed. The proposed antioxidant action of amino acid was divided into 2 stages; (1) condensation of amino acid under high temperature aging or vulcanization of the rubber and (2) chain breaking donor reactions. This division would offer a method of controlling the degradation of NR. The purity of solid NR was newly analyzed as the total content of 1,4 isoprene units in NR by 1H-NMR spectroscopy using polyethylene glycol (PEG) as internal standard for the signal intensity. Relative data was determined by calibration curve plotted between intensity ratio of methine proton (=CH) from 1,4 isoprene units against methylene protons (CH2) from PEG and molar ratio of NR and PEG. The effect of undissolved gel on the determination of 1,4 contents in NR was studied. Different grades of commercial solid NR, i.e., ENR-50, STR-20, SMR-L, SIR-20, RSS-1 and SVR-CV60, showed the total 1,4 contents of 43.4- 94.2%. The accuracy of the new method was found to be higher than that of the conventional 1H-NMR analysis by about 1%. This finding proved that the new approach provides new information on rubber purity by detecting the total isoprene units in the polyisoprene rubber.

Mahidol University

Address: NAKHONPATHOM

Email: liwww@mahidol.ac.th

Name: Jitladda Sakdapipanich

Role: Thesis Advisors

Created: 2008

Modified: 2553-06-22

Issued: 2010-06-16

วิทยานิพนธ์/Thesis

application/pdf

CallNumber: TH S961c 2008

eng

DegreeName: Doctor of Philosophy

Level: Doctoral Degree

Descipline: Polymer Science and Technology

Grantor: Mahidol University

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