Molecular Structure of Natural Rubber and Its Characteristics Based on Recent Evidence

Natural rubber (NR) latex collected from the Hevea trees exists as a colloidal suspension (Verhaar, 1959). The amount of latex obtained on each tapping is about 300 mL. The tapping is usually done once every 2–3 days for 9 months each year. Usually, the collected latex is treated with formic acid to coagulate the suspended rubber particles within the latex (Gazeley et al., 1988). After having been pressed between rollers to consolidate the rubber into 0.6-micrometre in thickness slabs or thin crepe sheets, the rubber is air-dried or smokedried for shipment. These rubbers are known as air-dried sheet (ADS) and ribbed smoked sheet (RSS), respectively. The treatment of latex with NaHSO3 is used to produce rubber of pale color, termed pale crepe. The other forms of rubber as block rubber are known as Standard Malaysian Rubber (SMR) or Standard Thai Rubber (STR), which are mainly graded by dirt content.