Research on the effect of the ratio of sodium bicarbonate on the mechanical properties of underarm crutch pads from natural rubber SIR-20 has been carried out. The ratio of sodium bicarbonate used was 1.00 phr; 1.50 phr; 2.00 phr; and 2.50 phr. The rubber compound for underarm crutch pads was made by the compounding process using an open rubber mixing mill and vulcanization at a temperature of 120 °C for 11 minutes. The best formula for curing characteristic rheometer test results at a temperature of 150 °C was URC-04 with Smax = 4.95 kg/cm, Smin = 0.44 kg/cm, ΔS = 4.51 kg/cm, t90 = 6.57 min and ts2 = 4.13 min. The mechanical test result showed the hardness test before aging and after aging of 31 Shore A, and 32 shore A, tear strength of 8.50 kN/m, elongation at the break before aging and after aging of 300%. The results of the identification of functional groups by FTIR for infrared absorption in each sample generally showed the same pattern with one another. SEM analysis result showed the distribution of materials and the formation of pores by sodium bicarbonate was not evenly distributed with an average diameter of 5 microns.

Tube collar is a part of quad cane type patient sticks. Its function is to adjust the height of the stick when used. The materials widely used to make tube collars are plastic. This study aims to study the mechanical properties of tube collars made from natural rubber composite materials with ethylene propylene diene monomers. Natural rubber and ethylene propylene diene monomers vary in ratios (70: 30; 80: 20; 90: 10; and 100: 0) phr. The activator, coactivator, softener, filler, accelerator, antioxidant and vulcanizing agent are conditioned. The experiments were carried out through the process of mastication, compounding and vulcanization. Vulcanization is carried out at 135 °C for 8 minutes. Curing characteristic test results with a rheometer at a temperature of 150 °C showed ΔS maximum of 9.70 kg/cm, maturation time (t90) 4.59 min, and scorch time (ts2) 0.02 min. The results of testing the mechanical properties of vulcanized rubber showed that the difference in the ratio of natural rubber with ethylene propylene diene monomer affects the mechanical properties of vulcanized rubber.

Research on the use of liquid natural latex for waterproof canvas fabric coatings has been carried out by varying the volume of liquid natural latex in 4 levels, namely 0.5 liters, 1.0 liter, 1.5 liters, 2.0 liter, and varying the thickness of the coating material 10 g, 20 g, 30 g so that 12 types of waterproof canvas are obtained. The purpose of this study was to find the right formula in the manufacture of canvas fabric that has the properties of Water Resistance, Adhesion, Tensile Strength, Elongation at Break, and Tear Resistance according to the quality standards of woven fabrics for tents. The results of testing the physical properties of waterproof canvas fabrics as a whole almost meet the quality standards of woven fabrics for tents, except for the results of the waterproof strength test at a layer of 10 g. The best results were obtained in formula III with a coating of 20 g, getting water resistance values of 43.6 mBar, adhesive strength 0.8 kg/cm, tensile strength 88.2 kg and 77.8, elongation at break 40.8% and 20, 3%, Tear strength 21.5 kg and 19.4 kg for warp direction and weft direction.

Kaolin is a mining material widely used as a filler in the manufacture of various types of finished goods made from natural rubber. Kaolin in this study was used as a special filler for solid tires for two-wheeled electric scooters commonly used by children. The purpose of this study was to determine the effect of the kaolin loading on the curing properties of the rubber compound, the mechanical properties of the vulcanizate, and the thermal properties of the rubber vulcanizate. Kaolin loading was varied from 22 to 42 per hundred rubber. The compounds were mixed on a two-roll mill. The vulcanization process took place at 140 °C for 17 minutes. The test results showed that kaolin loading had a strong effect on the maximum torque, scorch time, optimum vulcanization time, and mechanical properties of the vulcanizate. Thermo gravimetric analysis showed that the thermal stability of the vulcanizate was influenced by kaolin loading.

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