PST104 Prod. Proc. of Conventional Grade Final PDF

PST104 (BASIC NATURAL RUBBER PROCESSING) PRODUCTION PROCESSED OF CONVENTIONAL GRADES PREPARED BY: NOR MAZLINA ABDUL WAHAB 1 PRODUCT ION PROCESS 1 2 3 OF RIBBED AIR DRIED WHITE & CONVENT SMOKE SHEET (RSS)...

PST104 (BASIC NATURAL RUBBER PROCESSING) PRODUCTION PROCESSED OF CONVENTIONAL GRADES PREPARED BY: NOR MAZLINA ABDUL WAHAB 1 PRODUCT ION PROCESS 1 2 3 OF RIBBED AIR DRIED WHITE & CONVENT SMOKE SHEET (RSS) SHEET (ADS) PRODUCTIO PALE CREPE PRODUCTIO N IONAL PRODUCTIO N N GRADE 2  NR in sheet form is the oldest and most popular type. Being the simple and easiest to produce on a small scale, smallholders’ rubber in most countries is processed and marketed as sheet rubber. Raw rubber sheets in warehouse From the end user’s perspective, two types of sheet rubbers are produced for the commercial market: RSS and ADS. Of the two, RSS is the most popular due SHEET RUBBER to its mechanical properties and high tensile tensile strength. 3  WHAT IS RSS? RSS rubbers are made from intentionally coagulated whole field latex. They are classified by visual evaluation. To establish acceptable grades for commercial purposes, the International Rubber Quality and Packing Conference prepared a description for grading, and the details are given in The Green Book. 4 PRODUCTION OF RSS 1. Whole field latex used to produce RSS is first dilute to 15% solids (DRC) and then coagulated for around 16 h with dilute formic acid. 2. The coagulated material is then milled, the water is removed, and the material is sheeted with a rough surface to facilitate drying. 3. Sheets are then suspended on poles for drying in a smokehouse for 2-4 days (57°C) 4. Only deliberately coagulated rubber latex processed into sheets, properly dried, and smoked can be used in making RSS. 5. A number of prohibitions are also applicable to the RSS grades. 6. Wet, bleached, undercured, and original rubber and rubber that is not completely visually dry at the time of the buyer’s inspection are not acceptable (except slightly undercured rubber as specified for RSS 5). 7. Skim rubber made of skim latex cannot be used in whole or in part in patches as required packing specifications defined in The Green 5 STANDARDISATION OF FIELD LATEX (RSS) Producers usually standardise to 15% DRC and the volume of water added may be calculated as follow: dF x VF = dS x VS Where, dF= DRC field latex, VF=Volume field latex dS= DR C standardised field latex, VS= Volume Standardised field latex Hence, volume of water (VW) to add is VS-VF VS= dF x VF/dS 6 STANDARDISATION OF FIELD LATEX (RSS) Example: The volume of water required to standardise 2000 litres of 35% DRC latex to 15% is: VW = VS – VF = (35 x 2000)/15 – 2000 = 2667 litres 7 RSS Table 1.2 provides a summary of the criteria followed by inspectors in grading RSS. The darker the rubber, the lower the grade. The premium grade is RSS 1, and the lower quality grade is typically RSS 4. RSS 1 8  RSS are used when extra tough (due to extensive cross linking) rubber is needed Some applications are : Tanks Tubes Extruded hoses Footwear Tyres Quality Footwear Items APPLICATIONS OF RSS 9 ADS ADS are prepared under conditions very similar to those for smoked sheets but are dried in a shed without smoke or additives, with the exception of sodium bisulphite. Such rubber therefore lacks the antioxidation afforded by drying the rubber in a smokehouse. This material can be substituted for RSS 1 & RSS 2 grades in various applications 10  Crepe is a wrinkle lace rubber obtained when coagulated latex is selected from clones that have a low carotene content. Sodium bisulphite is also added to maintain colour and prevent darkening. After straining, the latex is passed several times through heavy rolls called creepers, and the resultant material is air-dried at ambient temperature. There are different types of crepe rubber depending upon the type of starting materials from which they are produced. Sri Lanka is the largest producer of pale crepes and sole producer of thick pale crepe The specifications for the different CREPE RUBBER types of rubbers for which grade descriptions are given in The Green Book are as follows: 11  Pale crepe is used for light-colored products and therefore commands a premium price. Threes or clones from which the grade is obtained typically have low yellow pigment levels (carotenes) and greater resistance to 1. PALE oxidation and discoloration. There are 8 grades in this category. LATEX All these grades must be produced from the CREPES fresh coagula of natural liquid under latex under conditions where all processed are quality controlled. The rubber is milled to produce both thin and thick crepes. Pale crepes are used in pharmaceutical appliances such as stoppers and adhesives (Table 1.3). 12 WHITE & PALE CREPES Table 1.3 shown the specifications in The Green Book for the different grade of white & pale crepes rubbers. PALE CREPE RUBBER 13  2. ESTATE BROWN CREPES All six grades are made from cup-lump and other higher grade rubber scrap Powerwash mills are to be (field coagulum) generated There are six grades in this used in milling this grades on the rubber estates. category into both thick and thin Three bark scrap, if used, brown crepes (Table 1.4). must be precleaned to separate the rubber from the bark. 14 ESTATE BROWN ESTATE BROWN CREPES CREPE RUBBER 15 3. THIN BROWN CREPES (REMILLS) These grades are Three bark scrap, if Inclusion of earth manufactured on used, must be scrap and smoked There are four powerwash mills precleaned to scrap is not grades in this class from wet slab separate the permissible in or category. unsmoked sheets rubber from the these grades (Table at the estate or bark. 1.5). smallholdings. 16 4. OTHERS- THICK BLANKET CREPES (AMBERS), FLAT BARK CREPES, PURE SMOKED BLANKET CREPES 1. Thick Blanket Crepes (Ambers) The three grades in this category are also produced on powerwash mills from wet slab unsmoked sheets, lump, and other high-grade scrap (Table 1.5). 2. Flat Bark Crepes The two grades of rubber in this category are produced on powerwash mills out of all types of scrap NR in compounded form, including earth scrap (Table 5.1) 3. Pure Smoked Blanket Crepe These grades is made by milling on powerwash mills smoked rubber derived from RSS (including block sheets) or RSS cuttings. No other type of rubber can be used. Rubber of this type must be dry, clean, firm, and tough and must also retain an easily detectable smoked sheet odor. Sludge, oil spots, heat spots, sand, dirty packing, and foreign matter are not permissible. Color variation from brown to very-dark brown is permissible. (Table 1.5) 17 18 THANK YOU 19