The dynamic mechanical properties of natural rubber vulcanizates containing aluminium powder have been compared  with those containing conventional fillers. Storage modulus, loss modulus· and loss factor increased continuously  with increase in aluminium  powder loading. The effect of various  bonding  agents like hexamethylene  tetramine-resorcinol  system, bis [3-(triethoxy silyl) propyl] tetrasulphide, cobalt naphthenate and toluene diisocyanate have been investigated. Presence of bonding  agents increased  the dynamic modulus  and mechanical loss due to improved adhesion. With increase in temperature  mechanical loss decreased. Variation in testing frequency affects dynamic properties, which decreased as the frequency decreased. Various theoretical models have been used to fit the experimental viscoelastic data.

An experiment was conducted at the Regional Experiment Station of Rubber Research Institute of India at Nagrakata  from 1989 to find out the nutritional  requirement of Hevea in northern  West Bengal.  Treatments included four levels of nitrogen (N) and three levels each of P₂O₅ and K₂O in factorial randomised  block design.  Nitrogen significantly influenced girth, girth increment (GI) and percent  tappability while P and K failed to show any direct effect. Application of 40 kg N per ha recorded significantly higher girth, GI and percent tappability over no N.  Soil and leaf nutrient status was not influenced by N application. However, P and K application significantly influenced the respective leaf nutrient status.  DRIS indices for different nutrients indicated the order of limiting nutrient as K>N>P. Interaction between N and K significantly influenced the percent  tappability. Significant linear increase in percent tappability with K levels was observed only in the absence of N but with the N percent  tappability did not increase significantly with K levels. Phosphorus and interaction between N, P and K significantly influenced the average yield (g/tree/tap) and estimated annual yield (kg/ha). Phosphorus showed significant negative effect on yield. The control (N₀ P₀ K₀) recorded significantly higher average yield (32.7 g/t/t) compared to other treatment combinations except N₄₀:P₀:K_40, N₂₀:P₀ :K₂₀,  N₄₀ :P₀:K₀,  N₀:P₂₀:K₄₀ and N₀:P₂₀:K₂₀.  However, estimated annual yield taking into account the percent  tappability was significantly higher with N₄₀:P₀ :K₄₀ (1223 kg/ha) compared to control (764.2 kg/ha). Hence fertilizer mainly helped in better growth resulting in reduced immaturity period and higher percent tappability. Bark thickness and yield components like dry rubber content were also significantly influenced by fertilizer application.

Drying is one of the most critical steps in the processing of latex into dry forms of natural rubber. Sheet rubber, which predominates  the Indian rubber market, is conventionally  dried in smoke. However, owing to various constraints, many small growers resort to at least partial drying in the open sun.   In the present study different modes of sun drying are compared with smoke drying. The effect of ultra-violet light on the raw rubber properties has also been studied.   It is observed that Po, Mooney viscosity and gel content increase while PRI decreases as a result of sun drying. The results indicated  that unless exposed to sun for prolonged periods, the raw rubber and the breakdown properties are not affected significantly. A slight over-exposure of sheet to direct sun­light will not adversely affect the initial vulcanizate properties of the rubber but its ageing proper­ties are found to be inferior.

An understanding of the numerous soil factors affecting soil fertility is a prerequisite to proper management  of soils for better growth and yield of Hevea. Soil samples collected from 14 sites planted with clone RRII 105 in 1994 spread out in Thrissur district of Kerala State were analysed for pH, organic carbon, available P, exchangeable Ca, Mg, K, Na and AI and DTPA extractable Fe, Mn and Zn. The data subjected to factor analysis using varimax rotation showed that there were two major factors indicating the latent structure, which included soil reaction control factor and P limiting factor. It was seen that the former factor got higher positive loading from exchangeable Ca, Mg, K, and Na while exchangeable AI and DTPA-Zn contributed negatively. The latter factor is regulated positively by pH and Mn and negatively by exchangeable AI and P. Regression analysis of tree volume and factor scores revealed that P limiting factor essentially influences the plant growth.

Rubber seed  oil has been evaluated as an acid acceptor  and  plasticizer in gum and  carbon black filled polychloroprene compounds replacing magnesium oxide and  naphthenic type  process oil. The results  of the study indicate that use of rubber  seed oil helps  to achieve better  scorch safety,faster cure rate and better ageing resistance in polychloroprene compounds. It can replace magnesium oxide and process oil in carbon black filled polychloroprene compounds. Use of rubber seed oil gives comparable tensile and  tear strength and better abrasion resistance for the carbon  black filled polychloroprene vulcanisates. Vulcanisates containing rubber  seed oil do not develop fungus on their surface.

The morphology of conidia and growth rate of isolates of the fungus causing raised, anthracnose and papery lesions of Colletotrichum leaf disease on rubber were compared.   The isolates produced morphologically uniform conidia on potato dextrose agar (PDA). Conidial shape was more useful than size in differentiation of isolates. Growth rate of the isolates from raised lesions was significantly lower than that from anthracnose and papery lesions. The latter two appeared  to be similar.  In general, the isolates from raised lesions produced pink pigmentation on PDA while those from anthracnose and papery lesions produced grey pigments.  The isolates from raised lesions were of Colletotrichum acutatum, distinct from anthracnose and papery lesion isolates which were of C. gloeosporioides.