Non-rubbers

Synthetic resins are extensively used, e.g., in surface finishes, in the fabrication and repair of boat and motor vehicle bodies, in the manufacture of laminated boards, for electrical components, in pattern making and in paints and varnishes. Non-rubber adhesives made from fish glues and from cotton derivatives (e.g. cellulose acetate) tend not to be sensitizing but, depending upon composition and the manner of use, many other types may pose significant dermatitic and fume hazards. 

When natural rubber latex is concentrated by centrifuging there are produced approximately equal volumes of concentrate containing most of the rubber, and skim latex with a low proportion of rubber. The rubber obtained by coagulation of skim latex is termed skim rubber. Due to the high content of non-rubber substances such rubber may give difficulty in processing. 

NR is c/ s -1,4-polyisoprcnc, of molecular weight 200,000-500,000, but it also contains a small level of highly important non-rubber constituents. Of these, the most important are the proteins, sugars and fatty acids which are antioxidants and activators of cure. Trace elements present include potassium, manganese, phosphorus, copper and iron which can act as catalysts for oxidation. 

Due to the absence of the non-rubber constituents present in the NR some differences in compounding occur, although, in essence, the principles are the same. An increased level of stearic acid is generally required for cure activation and approximately 10% extra accelerator is necessary to achieve a similar cure rate to NR similar sulphur levels are, however, used. IR can be cured by the same type of systems as NR. 

Natural Rubbers (NR). The chemical name for NR is polyisoprene, which is a homopolymer of isoprene. It has the cis-1,4 configuration. In addition, the polymer contains small amounts of non-rubber substances, notably fatty acids, proteins, and resinous materials that function as mild accelerators and activators for vulcanization. Raw materials for the production of NR must be derived from trees of the Hevea Brasiliensis species. NR is available in a variety of types and grades, including smoked sheets, air-dried sheets, and pale crepes. 

Synthetic Polyisoprene Rubbers (IR). IR is a cis-1,4 polyisoprene synthetic natural rubber. However, it does not contain the non-rubber substances that are present in NR. One can differentiate between two basic types of synthetic polyisoprene by the polymerization catalyst system used. They are commonly referred to as high cis and low cis types. The high cis grades contain approximately 96-97% cis-1,4 polyisoprene. 

NR latex contains about 35wt% natural rubber hydrocarbon as particles that are about 1 pm in diameter and about 5% non-rubber components... 

Composite Particles, Inc. developed two methods of surface modification of polymeric materials which are used for materials of different shapes and compositions. Here, only the spherical, non-rubber particles are discussed. Further information is included in the section on rubber particles below. One method of surface modification is based on exposing the polymeric powder to a chemically reactive gas atmosphere which oxidizes surface groups to form OH and COOH functionalities. These functionalities are then available for reaction with the components of the matrix into which modified particles are introduced. Vistamer HD and UH are manufactured by this method from polyethylenes of different molecular weights. Two factors can be regulated here the properties of the core particle and the type and density of functional groups on the surface of these particles. Polyethylene is a material, which without this modification, will not be compatible with most systems. The surface modification allows the incorporation of the material into resins. This improves abrasion resistance, tear strength, and moisture barrier properties and reduces the fiiction coefficient. 

Hard rubber or ebonite whether from natural rubber or from synthetic rubber, can be defined as highly vulcanised rubber, containing a large proportion of combined sulfur. Hard rubbers made from natural rubber have vulcanisation coefficients between 25 and 47. The theoretical vulcanisation coefficient value for natural rubber is 47 and for synthetic rubbers it is in the range of 35 to 47. The coefficient of vulcanisation is usually defined as the number of units by weight of sulfur combined with 100 units by weight of unsaturated hydrocarbon. The theoretical coefficients are corrected for impurities/non rubber constituents in the raw rubber. 

Concentration of latex is necessary because of the preference by the latex products manufacturing industry for latex with high dry rubber content (DRC), and for transport economy and purification of the latex. The processes for concentration include evaporation, electrodecantation, creaming, and centrifuging. Evaporation removes only water and hence the ratio of non-rubber constituents to rubber, and the particle size distribution remain unchanged. However, the other three processes involve the partial removal of non-rubber materials and smaller rubber particles. Centrifuging and creaming are more popularly used for the production of concentrated latex. 

The density of natural rubber is about 0.913 g per cc, and its bulk density is about 0.85 g per cc. The rubber hydrocarbon content of raw natural rubber is about 94%. The presence of small quantities of non-rubber constituents such as proteins, fats, fatty acids, carbohydrates, and mineral matter in natural rubber influences its physical and chemical properties. 

However some non-rubber compounds are also called elastomers if they exhibit a nondeforming elastic property similar to rubber at room temperature, even if the compound is relatively hard. The two main groups of non-rubber elastomers are thermoplastics, e.g., polyvinyl chloride, polypropylene and thermosets, e.g., ethylene propylene rubber, cross-linked polyethylene. These two groups are also covered by the term plastic . 

Results and Discussion To contrast the thermal stability of rubber-modified epoxy resins, a control experiment was performed to establish the thermal stability of a non-rubber-modified epoxy resin. An advancement reaction was performed (EEW 900 g eq ), the product maintained isothermally at 175C, and the reaction progress followed by thermally quenching aliquots to room temperature at various time intervals. Although previously published reports indicate no significant increase in the EEW of an... 

NR latex is a suspension of NR particles with diameter from 0.05u to about 3.0 u in water. It also contains a smaller number of easily deformable bodies (lutoid), which consist essentially a viscous aqueous solution of non rubber particles, surrounded by a breakable membrane. NR latex which freshly- tapped from Hevea Brasiliensis containing about 367i dry rubber and 3V. non rubber materials (protein, fats, phospholipid, carbohydrate and nitrogen compound). 

The synthesis site for allylic diphosphate primers and cw-polyisoprene is largely assumed to occur on the surface of pre-existing rubber particles, but rubber biosynthesis activity has also been localized in the membrane of non-rubber particles from the bottom fraction after ultracentrifugation of latex. " The latter authors " presumed that previous localization of rubber biosynthesis on rubber particles was due to an artefact resulting from the rapid deterioration of bottom fraction (BF) particles after tapping, which led to the migration of rubber synthesis machinery from BF particles to rubber particles. 

Unlike rubber-degrading actinomycete colonies, fungal colonies on latex-agar plates are not surro mded by transparent zones [5]. Superficial growth of fungi on NR films has been observed with a negligible consumption of the rubber [10]. Growth of the molds on rubber may have proceeded at the expense of the non-rubber constituents, like proteins in these cases. 

Microbial degradation of synthetic rubbers will be a subject of fiirther study. A rubber product is made from a number of complex ingredients, and smaller molecules in a synthetic polymer (e.g., stearate, process oils, and waxes in vulcanized synthetic rubber) may be decomposed by microorganisms. A clear distinction must be made between the superficial growth of microorganisms on non-rubber constituents in a synthetic polymmrs and the biodegradation of the rubber hydrocarbon [23]. 

Latex compounds have been typically used in paper, textile and construction. One of the most popular applications is their use in self-sealing envelopes. This application is based on the fact that when NR dries, some soluble non-rubber compounds migrate to the surface by water transport, leaving a thin film when drying is completed. This film reduces the surface tack on the rubber, and when pressed against a similar film, the non-rubber layer is displaced, allowing the two rubber surfaces to create a bond. 

Use clean polymers, free from excessive levels of non-rubber materials. 

NR can also be exported as concentrated latex. Fresh field latex consists of 30-40% dry rubber content (DRC), the other 60-70% being mainly water-containing non-rubber substances. The non-rubber components, e.g. proteins, carbohydrates, lipids and inorganic salts, vary according to clones, season and age of rubber tree. The latex collected from the plantation is preserved with ammonia (NH3) and then undergoes continuous centrifugation to produce the... 

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