Moulding rubber latex

SBR also finds use in conveyor belts, moulded rubber goods, shoe soles, hose and roll coverings. SBR is also available as a latex which is used in carpet backing and other applications. 

The production of foamed rubber by whipping a latex is known for a long time. Rubber mattresses are still being made in this way. The latex is whipped into a foamy substance and then poured into a mould. The water is evaporated, and the rubber is vulcanised with the aid of vulcanization ingredients (sulphur etc.) added before to the latex. The density of a rubber latex foam for mattresses is about 70 kg/m3. 

This moulding process is normally applied to a rubber latex or plasticised PVC (plastisol) whereby a solid shape is dipped into a mobile liquid. When the material has set the formed shape is stripped from the mould. 

The finished dry rubber and latex based rubber products can be vulcanized by several techniques depending on the type of rubber compound (dry rubber compound/latex compound), size of the finished product, and its shape and structure. Moulded rubber products are vulcanized by press curing using compression, transfer, or injection moulding presses. The vulcanization techniques other than moulding may be grouped into batch and continuous methods. The batch methods include the use of autoclaves, hot air/gas oven, and hot liquid/ water bath. Rubber products may be vulcanized at room temperature by cold curing either by immersion of rubber products in a carbon disulphide solution of sulphur chloride (SjCy, or by exposure to its vapour. 

Rubber latex has been widely used since the 1930s as a moulding material (von Fuehrer, 1938 Watkinson, 1982). The prevulcanized latex is applied to... 

Fig. 5. Dynamic compression characteristics of cored rubber latex, conventional moulded polyurethane and high resilience moulded polyurethane foam.

Since 1960, the inner core has been made from c/5-poly-butadiene by the compression moulding technique. This replaced the earlier material made from a suspension of barytes or bentonite clay in water and glycerine or the winding of rubber threads made from t /5-polyisoprene, either from latex or a dry rubber compound. A typical thread recipe is given Table 4. 

A method of manufacturing rubber articles by pouring a compounded latex into an absorbent hollow mould the skin of rubber thus formed is removed, dried and vulcanised. The term is also apphed to the pouring into moulds of liquid polymer systems based on silicone or polyurethane elastomers. 

The mineral muscovite, mainly an orthosilicate of aluminium and potassium, finely ground and used as a lubricant in rubber moulding and as an extended filler in latex compounds. 

Jong et prepared NR composites reinforced with hybrid filler consisting of defatted soy flour (DSF) and CB. Aqueous dispersions of DSF and CB were first mixed, and then blended with NR latex and sulfur dispersion, respectively. The homogenous composite mixtures were quickly freeze-dried and compression moulded to offer the NR composites. They found that the NR composites reinforced with 40% of hybrid filler (the ratio of DSF to CB was 1 1) exhibited a 90-fold improvement in the rubber plateau modulus compared with unfilled NR, showing a significant reinforcement effect by the hybrid filler. 

Mondragon et al ° reported that unmodified and modified NR latex were used to prepare thermoplastic starch/NR/MMT nanoeomposites by twin-screw extrusion. After drying, the nanoeomposites were injection moulded to produce test specimens. SEM of fractured samples revealed that chemical modification of NR latex enhanced the interfacial adhesion between NR and thermoplastic starch (TPS), and improved their dispersion. X-ray diffraction (XRD) showed that the nanoeomposites exhibited partially intercalated/exfoKated structures. Surprisingly, transmission electron microscopy (TEM) showed that clay nanoparticles were preferentially intercalated into the rubber phase. Elastic modulus and tensile strength of TPS/NR blends were dramatically improved from 1.5 to 43 MPa and from 0.03 to 1.5 MPa, respectively, as a result of rubber modification. 

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