Abstract:
Natural Rubber Latex Foam (NRLF) is a cellular rubber, which is made directly from
centrifuged latex with 60 % dry rubber content and it gives a cushioning effect for a wide range
of applications such as mattresses, pillows, cushions, upholstery, carpet backing and shoe
arches. If there is a possibility of replacing a certain amount of natural rubber latex in these
products, while maintaining the expected physico mechanical properties by incorporating
another low cost material (filler), it would reduce the cost of production. Therefore a study was
conducted to develop different natural rubber latex foam by incorporating five types of
commercially available mineral fillers in five different loading levels. Fillers can stiffen the
rubber phase of the foam. Therefore comparable load bearing characteristics can be obtained at
higher expansion with the incorporation of filler (Blackley, 1966). There by material cost can be
decrease.
Methodology
Samples were prepared by incorporation of talc, dolomite, calcite, 50:50 blend of dolomite and
calcite and china clay as filler materials. Each of these fillers was incorporated in NR latex foam
at 5 phr, 10 phr, 15 phr, 20 phr and 25 phr loading levels.Latex foam was prepared using a batch
technique. The foam preparation was carried out in a Hobart type planetary mixer.
To develop twenty five different foams all of these were replicated three times and they were
arranged in Complete Random Design. Indentation hardness index, compression set, tensile
strength and density properties of the test samples were compared against the reference sample
which was prepared without incorporating fillers.
Results and discussion
Hardness of the compound increases with the increase of calcium carbonate filler loading up to
20 phr and it decreases beyond this filler loading. The increase in hardness may be due to fillers
acting as hardening agents in rubber compounds and uniform filler distribution in the rubber
phase. At higher filler loadings beyond 20 phr, the decrease in hardness is probably a result of
aggregation of calcium carbonate.
