Comparison study on the mechanical, thermal, chemical and oil resistance properties of hydroxylated natural rubber, SMR L and EPDM / Nurul Wahidah Che Zahari

Hydroxylated natural rubber (HNR) prepared from natural rubber (NR) is a new sustainable elastomer with better-swelling properties. Rubber modification technologies have created new approaches based on the hydroxylation process using hydroxoformic acid to reduce the double bond. NR latex was hydroxylated in one pot solution method with in-situ performic acid at different duration times; 10, 20, 30, 40 and 50 hours of reaction. The effect of the reaction time, stirring speed, temperature and pH value of modified NR latex were discussed. The result shows the optimum condition for producing 25% of hydroxyl number with a ratio of 10:1:1 during the reaction time at 40 hours. The observations also revealed from the synthesis the best performance was recorded when the stirring speed was 300 rpm, the temperature at 2°C and pH value to be 9. The determination of Total Solid Content (TSC) and Dry Rubber Content (DRC) of hydroxylated NR was studied and the average percentage of TSC and DRC decreased with increasing the different reaction times. Fourier Transform (FT) Raman spectroscopy was used to analyze the conversion of hydroxylation. The result shows the double bond's optimum conversions to hydroxyl functionality were recorded highest at 40 hours and remained constant, although the reaction was continued until 50 hours. Based on NMR characterization, the hydroxyl contents of the in situ hydroxylated natural rubber (HNR) were about 25% to 30 mol %. On the other hand, the onset of modified natural rubber's thermal degradation was recorded at 220°C compared to the unmodified natural rubber. HNR exhibited a shorter cure time due to the accelerator used is N-cyclohexylbenzothiazole-2-sulphenamide (CBS), compared to the SMR L and EPDM. EPDM gave the shortest scorch time, and optimum cure rate since used tetramethylthiuram disulphide (TMTD) as an accelerator. For both HNR and SMR L samples, it shows that SMR L has the highest hardness value. However, the tensile strength of HNR vulcanizate was drastically decreased compared to SMR L and EPDM compounded rubber. It has been reported the SMR L has a greater amount of gel content compared to HNR. Different compounded rubber's oil resistance was investigated by being immersed in two different solvent oil IRM 901 and IRM 903. HNR results in a higher swelling value than SMR L and EPDM. This is because HNR is a polar rubber; therefore, it exhibits excellent oil resistance and better crosslink density. HNR is considered to replace EPDM because it is low-cost, simple to obtain, can produce in mass manufacturing and easy to control. Finally, it can be recommended from the synthesized HNR can produce the chlorination rubber by introducing hydrochloric acid to the side reaction of HNR, which leads to rubber hydrochloride structures