Effect of mixing conditions on money viscosity of deproteinized natural rubber

Abstract

Constant-viscosity deproteinized rubber (CV-DPNR) is obtained by removing protein from latex by using Papain or Alcalase enzyme, and the viscosity is made near constant by adding hydroxylamine hydrochloride as inhibitor. The advantages of CV-DPNR is its resistance to storage hardening and their improvement of the physical properties and dynamic properties which are suitable for engineering applications. The main objective of this research is to study the correlation between agitation speed and initial Mooney viscosity of raw rubber, rate of increasing Mooney viscosity of CV-DPNR during storage and the optimal agitation speed for latex deproteinization. The results indicate that the most suitable agitation speed is 60 revolutions per minute under optimal conditions for Papain at 50oC, pH 7.6 and one hour of operation. It is found that for the turbulence intensity factor between 50 to 58 the nitrogen reduction of 84-88 percent can be obtained. For Alcalase deproteinization at 60oC, pH 8.5 and 4 hours of operation, only 72% nitrogen reduction was observed. For turbulence intensity factor over 58, the protein reduction rate decreases because of the agglomeration of the rubber particles in the latex. For the turbulence intensity factor under 50, the protein reduction rate also decreases due to the insufficient energy of agitation to promote enzymatic reaction for the digestion of protein in the latex. When the raw rubbers of different nitrogen contents obtained from various agitation speeds were stored at room temperature for 6 months, it is evident that rubbers prepared at agitation speed 60 revolutions per minute has the least increasing rate of 0.17 Mooney unit per month. Comparative study on the rate of increasing Mooney viscosity in 3 rubber clones between CV-DPNR and CV-rubber during long-term storage for 12 months at room temperature showed that clone RRIM 600 has the lowest rate of increasing Mooney viscosity followed by GT 1 and PB 5/51 respectively. (0.12, 1.82 and 1.87 Mooney unit per month) This indicates that different sizes of tuber particles in rubber clones need agitation at different turbulence intensity factor for optimal conditions. Testing of raw rubber physical properties confirms that CV-DPNR has nitrogen content, ash, dirt, volatile matter, Mooney viscosity and color index lower than the constant-viscosity natural rubbers. For the cure characteristics, CV-DPNR has a longer scorch time but a faster cure rate for RRIM 600 and lower cure rate for GT 1 and PB 5/51. Testing for the vulcanizate properties indicates that CV-DPNR has higher tensile strength, tear strength and percent elongation at break, whereas the 300% modulus and hardness are lower as compared to the constant-viscosity natural rubbers. These improvements on physical and dynamic properties were observed in all 3 rubber clones.