What is Latex?
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| Rubber tree |
About Latex
Natural latex is a milky liquid secreted by a variety of plants that grow in the tropics. It is not a sap, and its function in the plant is not well understood. The latex produced by the rubber tree contains about 30 to 40% rubber hydrocarbon (polyisoprene) suspended in water. Today, the term latex applies not only to the natural suspensions but also to suspensions of synthetic rubber and synthetic elastomers. Some of these synthetic materials are: styrene-butadiene copolymers, acrylonitrile-butadiene (nitrile) rubbers, chloroprene rubbers, acrylic copolymers, synthetic cis-polyisoprene, vinyl acetate co-polymers, vinyl chloride copolymers and butyl rubber.
Natural latex is a milky liquid secreted by a variety of plants that grow in the tropics. It is not a sap, and its function in the plant is not well understood. The latex produced by the rubber tree contains about 30 to 40% rubber hydrocarbon (polyisoprene) suspended in water. Today, the term latex applies not only to the natural suspensions but also to suspensions of synthetic rubber and synthetic elastomers. Some of these synthetic materials are: styrene-butadiene copolymers, acrylonitrile-butadiene (nitrile) rubbers, chloroprene rubbers, acrylic copolymers, synthetic cis-polyisoprene, vinyl acetate co-polymers, vinyl chloride copolymers and butyl rubber.
All latices, both natural and synthetic, are shear-sensitive to varying degrees. This means that under shear these materials can coagulate. Raw natural latex is matured with time to produce a more stable product. If raw latex is not allowed to mature, processing becomes very difficult because of agglomeration. Raw latex may contain soaps and ammonium hydroxide to maintain stability. This shear instability makes it difficult to process latices with high shear equipment such as mixers or colloid mills. However, the homogenizer has been extremely successful in this operation. The success of the homogenizer is due to the fact that the instability of latex is a function of the degree of shear and the time to which it is exposed to this shear. In the homogenizing valve the degree of energy input is high, but the time is essentially zero, thus permitting the processing of the most shearsensitive latices with the minimum of coagulation. However, even in the best processing conditions, latex may agglomerate inside the homogenizer pump requiring routine cleaning of the machine to maintain good pumping action.
The homogenizer has a number of applications in the processing of latex. The following list indicates the diversity of its usage in the field.
The homogenizer has a number of applications in the processing of latex. The following list indicates the diversity of its usage in the field.
- Dispersion of compounding ingredients in latex.
- Agglomerating or growing of latex particles.
- Manufacture of latex thread or filaments.
- Master-batching of latex prior to coagulation. (Carbon black or other reinforcing agents)
- Pigmenting of latices.
- Incorporation of extending oils to latices.
- Plasticizing of latices.
- Reduction of agglomerates in synthetic latices.
Objectives for Latex
The objectives for these various latex applications cover a range of goals that sometime seem contradictory. For example, a latex particle can be either increased or decreased in size by the same piece of equipment; i.e., the APV homogenizer, depending upon the conditions of operation and the type and percentage of surfactant present in the formulation. A brief summary of the objectives for each application follows.
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