Publication: Effect of different type of coagulants and serum ph on the properties of natural rubber compounds and vulcanizates
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Date
2023-07-01
Authors
Ng Jing Wei
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Abstract
Natural rubber (NR) is the main component used in tyre industry that is
extracted naturally from Hevea Brasiliensis in latex form and further transformed into
dried rubbersheet. In the first experiment, the latex was coagulated with different types
of coagulant, which are formic acid, sulfuric acid, CaCl2, methanol and spontaneously
without addition of coagulant. After processing, the raw rubbers produced from the
respective coagulants were subjected to different testing from the perspective of
coagulation process, raw rubber, masterbatch, final mix compound and finally
vulcanizate in tyre tread formulation. Being the most efficient coagulant, sulfuric acid
displayed poorer properties in raw rubber with oxidized rubber sheets and higher
amount of short rubber chains as indicated in AE content and Mw. In contrast, natural
coagulation was demonstrated to be least efficient, but the raw rubber was tested to
have highest molecular weight and macrogel content. The Mw of raw rubber and
macrogel content were shown to be well correlated to the VR and P0. Besides, the
selection of coagulant type was found to have impact also on the N and metal ions
content of raw rubber. However, the impact of coagulant type on the BdR of
masterbatch, Payne effect and VR of final mix compound was indirect depending on
the Mw and VR of raw rubber. Accelerating effect of natural proteins and retarding
effect of sulfuric acid were also observed in curing properties. The physical mechanical properties of vulcanizate were mainly influenced by the crosslink density of vulcanizate. The type of coagulants used displayed no significant influence on the
wet grip and rolling resistance properties of vulcanizate. In the second experiment, the
latex was coagulated with formic acid and sulfuric acid respectively, in serum pH 4
and pH 2. The most notable impact of serum pH was the efficiency of coagulation
process, VR and P0 of raw rubber. It was shown that the impact of acid type on the raw
rubber properties was less important if the serum pH was controlled on same level
except PRI. However, the impact of serum pH on other properties of raw rubber were
not significantly observed. After addition of compounding ingredients, the properties
of masterbatch, final mix compound and vulcanizate displayed no significant
differences between different serum pH suggesting the compounding ingredients play
more important role to decide the properties of vulcanizate.