PRI ageing and some related properties of constant viscosity natural rubbers

Eng A. H., . and Chang C. F., . and Kawahara S., . PRI ageing and some related properties of constant viscosity natural rubbers. pp. 199-208. ISSN 1511-1768

Constant viscosity natural rubber (NR) samples from different clones showed no correlation between copper content and Plasticity Retention Index (PRI) value. When the NR samples were stabilised with hydroxylamine the degree of storage hardening was low but the PRI remained high. The gel content of the NR samples decreased significantly after the PRI test. The extent of reduction in gel content was much greater than that of the reduction in molecular weight of the NR samples. This was attributed to the denaturation of the proteins which led to the disintegration of crosslinks or higher rate of oxidation due to the presence of a high level of metal ions in the gel. The extent of molecular weight reduction was slightly lower than that of plasticity value. The Wallace plasticity could be correlated with the geometrical mean of Mn and Mw i.e. (MnMw)1/2. The correlations obtained from linear regression before and after PRI ageing were quite comparable probably because the NR samples were processed and aged under the same conditions. Activation energy of oxidation (AEO) determined by differential scanning calorimeter provided a more sensitive method of assessing the ageing resistance of NR samples than PRI. However the correlation between PRI and AEO was insignificant.

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Abstract

Constant viscosity natural rubber (NR) samples from different clones showed no correlation between copper content and Plasticity Retention Index (PRI) value. When the NR samples were stabilised with hydroxylamine the degree of storage hardening was low but the PRI remained high. The gel content of the NR samples decreased significantly after the PRI test. The extent of reduction in gel content was much greater than that of the reduction in molecular weight of the NR samples. This was attributed to the denaturation of the proteins which led to the disintegration of crosslinks or higher rate of oxidation due to the presence of a high level of metal ions in the gel. The extent of molecular weight reduction was slightly lower than that of plasticity value. The Wallace plasticity could be correlated with the geometrical mean of Mn and Mw i.e. (MnMw)1/2. The correlations obtained from linear regression before and after PRI ageing were quite comparable probably because the NR samples were processed and aged under the same conditions. Activation energy of oxidation (AEO) determined by differential scanning calorimeter provided a more sensitive method of assessing the ageing resistance of NR samples than PRI. However the correlation between PRI and AEO was insignificant.

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Item Type:	Article
AGROVOC Term:	Natural rubber
AGROVOC Term:	Ageing
AGROVOC Term:	Viscosity
AGROVOC Term:	Clones
AGROVOC Term:	Copper
AGROVOC Term:	Plasticity
AGROVOC Term:	Hydroxylamine
AGROVOC Term:	Storage
AGROVOC Term:	Hardening
AGROVOC Term:	Molecular weight
Depositing User:	Ms. Suzila Mohamad Kasim
Last Modified:	24 Apr 2025 06:28
URI:	http://webagris.upm.edu.my/id/eprint/23179

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