Research article

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This work presents a simple processing way to vulcanize natural rubber (NR) using glutaraldehyde (GA) as a curing agent at low temperature. The effect of different protein contents of NR latex on the resulting properties of the NR vulcanizates is examined in this paper. The protein contents in different NR latex, including creamed-NR (CreNR), centrifuged-NR (CenNR), and synthetic-NR (SynNR) latexes, were successfully analyzed. It was found that CreNR has the highest protein content, followed by CenNR and SynNR, respectively. The influence of protein contents in NR latex on crosslink density, mechanical properties, and thermal stability of the cured NR were investigated and compared. Temperature scanning stress relaxation (TSSR) technique was used to examine the crosslinking among GA and protein molecules, which has inter-particle interactions with NR molecular chain. This was compared with the conventional swelling experiments used in determining the swelling ratio. It is found that the mechanical properties, thermal stability, and the crosslinking density data are strongly related to the protein content in the NR latex, i.e., CreNR > CenNR >Syn NR. This is attributed to the protein strong contacts of the protein content to the NR chain and its ability to propagate chemical crosslinking with GA molecules. Therefore, the protein causes new linkages between rubber molecules through GA.