1 Technical Note: NR-Latex & Latex Products Rubber Latex is a stable dispersion of polymeric substances in aqueous medium and is essentially a two phase system; 1) Disperse phase (discontinuous phase of rubber molecules) & 2) Dispersion medium (aqueous continuous phase of serum). Basically there are two types of lattices viz. Natural lattices and Synthetic lattices. Natural Rubber Latex (NR Latex) is the most widely used latex for the manufacture of latex based rubber products. Fundamental characteristics of lattices Lattices are complex colloid systems containing polymer molecules as major fraction. The polymer may be a homo polymer or co-polymer (random / block / graft). Stereo regularity and the complexity of the polymer molecules (linear / branched / cross linked) is maintained in the latex form. The avg-molecular size, molecular weight & molecular weight distribution of the latex depend on the grade selected. Lattices are rubbery or resinous in nature and the rubber molecules can be cross linked. Lattices can be plasticized or oil extended. Lattices have their own mechanical properties and temperature limits of serviceability. The rubber particle is generally oval having < 5 micron particle size and a typical particle size distribution. The aqueous phase consists of dissolved and suspended matters and knowledge of their concentration, acidic / basic nature (pH) is essential for successful latex compounding. Latex products are subject to degradation and adequate antioxidant protection is necessary. NR-LATEX Over 200 species of plants are found to yield NR latex on tapping. Only ‘Hevea Brasiliensis’ plant is of commercial importance and accounts for 99% of World’s NR production. On tapping the Hevea brasiliensis tree, NR-Latex exudes. Composition of field Latex : Material % By weight Total solids contents (TSC) 36 Dry rubber contents (DRC) 25-40 Proteins substances 1-1.5 Resinous substances 1-2.5 Ash Up to 1.0 Sugars Up to 1.0 Water Balance Two surface phases are present in latex viz. air aqueous phase interface (surface free energy of latex) and an aggregate of polymer-aqueous phase (Stability / Change). The manner in which surface-active substances are distributed in the two phases is of great significance for product manufacture. The Dispersed Phase (NR): Consists of small (approximately < 5 μ diameter) polymeric particles dispersed in serum with - ve surface charge (anions). Typical composition of the disperse phase is as follows:
Technical Note: NR-Latex & Latex Products
Jun 17, 2023
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