Rubber Science

VULCANIZATION KINETICS AND PROPERTIES OF NR-EVA BLENDSResearch Articles
Pages 77 - 87
Alex T. Koshy, Baby Kuriakose & Sabu Thomas
- Abstract
- Keywords
Blends of natural rubber (NR) and ethylene vinyl acetate (EVA), in varying proportions, were prepared with three different cure systems and evaluated for vulcanization kinetics and physical properties. The dicumyl peroxide (DCP) system required a higher energy of activation and longer cure time compared with the sulphur system and the mixed cure system consisting of DCP and sulphur. Most of the important technological properties were better for the blends vulcanized using the mixed cure system compared with those cured with DCP. The blends showed better abrasion resistance. higher hardness modulus and tear resistance as the proportion of EVA increased.

Natural rubber, Ethylene vinyl acetate, Vulcanization kinetics, Cure system, Blends

SEASONAL CHANGES IN PHYSIOLOGICAL CHARACTERISTICS AND YIELD IN NEWLY OPENED TREES OF HEVEA BRASILIENSIS IN NORTH KONKANResearch Articles
Pages 88 - 97
T. R. Chandrashekar, M. K. Jana, Joseph Thomas, K. R. Vijayakumar & M. R. Sethuraj
- Abstract
- Keywords
Seasonal changes in physiological characteristics and yield were studied in Hevea brasiliensis in the North Konkan region. This is a non-traditional rubber growing area where the crop experiences severe drought in summer months. The study was carried out in newly opened trees of clones GT 1 and RRIM 600. The per tap dry rubber yield in summer months was extremely low and not economical. The estimated first year yield ha^-1 for the remaining period was 493 kg for GT 1 and 549 kg for RRIM 600. The extreme soil and atmospheric moisture deficits resulted in very low plant moisture status and high plugging indices. Stomatal conductance and transpiration rates were also severely inhibited throughout the day. Partial defoliation and leaf margin drying were observed during this period. In general, RRIM 600 maintained relatively higher yield and plant moisture status.

Hevea brasiliensis, Drought tolerance, Yield components, Water relations, Konkan region

COMPARISON OF DIFFERENT METHODS OF YIELD ESTIMATION IN HEVEA BRASILIENSISResearch Articles
Pages 98 - 101
E. E. Aniamaka & E. O. Olapade
- Abstract
- Keywords
Five methods of estimating dry rubber yield were investigated in eleven clones of Hevea brasiliensis. The tapping system used was ½ S d/2 without stimulation. The conventional method of air-drying of cup-lumps was found to over-estimate yield. The Metrolac method gave values closer to those of the standard method, though not close enough to the required tolerance. Pending identification of an alternative method giving results within acceptable tolerance, the Metrolac method may continue to be used with reservation.

Hevea brasiliensis, Yield estimation, Dry rubber content, Metrolac method, Air dried cup lump

FACTORS AFFECTING TRANSPARENCY OF NATURAC RUBBER LATEX FILMSResearch Articles
Pages 102 - 110
N. M. Claramma, K. Mariamma George & N. M. Mathew
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- Keywords
The different factors affecting transparency of films made from natural rubber latex have been investigated. The effect of sulphur, zinc oxide, oil, antioxidant, fillers, viscosity modifiers, coagulants, type of latex and humidity were studied. As sulphur dosage is increased, transparency of NR latex film increases, reaches a maximum and then decreases. The presence of zinc oxide in the film decreases transparency. The particle size of zinc oxide affects transparency of the film. Paraffinic oil and styrenated phenol type antioxidant do not affect transparency of the films. Fillers decrease transparency considerably. Centrifuged latex and creamed latex give comparable transparency to the film. Clarification of prevulcanized latex and heat treatment of the film substantially improve transparency especially when clarification is done by centrifuging. Exposure of the films to a humid atmosphere decrease transparency. Films made by straight dipping are more transparent than those made by coagulant dipping.

Natural rubber, Compounding ingredients, Prevulcanized latex, Coagulants, Fillers, Viscosity modifiers, Antioxidants

FARM-GATE PRICE OF NATURAL RUBBERResearch Articles
Pages 111 - 115
B. Sreekumar, V. Haridasan & P. Rajasekharan
- Abstract
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A study was conducted to estimate the share of the producer in the consumers' price of natural rubber. The data collected from Kanjirappally and Changanacherry taluks of Kottayam district, showed that the producers' share in the consumers' price was 0.88, based on the weighted average price of sheet and scrap rubber. However, in the case of sheet rubber the producers' share was found to be 0.92.

Natural rubber, Farm-gate price, Price spread, Marketing cost, Concurrent margin

EFFECT OF RETARDERS ON CURE CHARACTERISTICS, KINETICS OF VULCANIZATION AND PHYSICAL PROPERTIES OF NATURAL RUBBERResearch Articles
Pages 116 -125
Sara Chandy & Baby Kuriakose
- Abstract
- Keywords
The effects of three retarders-benzoic acid, N-nitrosodiphenyl amine and N-(cyclohexylthio) phthalimide-on cure characteristics, kinetic parameters and physical properties of thiazole and sulphenamide accelerated natural rubber compounds were evaluated. The results indicated that the effect of the retarders depends on the type of accelerator used. The difference in the effect of the retarders on scorch and cure times of the compounds is explained based on kinetic parameters of the vulcanization reaction in the presence of the retarders. These observations agreed well with the already established reaction mechanisms of cure retardation.

Natural rubber, Accelerators, Retarders, Scorch time, Cure time, Sulphur, Vulcanization kinetics