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Modification of organic polymers adds to add-ons, with a few exceptions, a multiphase system containing additives incorporated into a continuous polymer matrix. The combination that results from a unique micro-structure or a unique micro-structure, which is the cause of the symptoms. The main reason for the use of additives is:
Improving and controlling of processing characteristics.
Property modification or enhancement.
Overall cost reduction
Types and Components of the Polymer Composites:
A polymer composite is a mixture of a polymer and an organic or inorganic additive with geometric certainties namely (flakes, spheres, fibres and particles). Therefore, they have more than one components and two or more phases. They are incorporated into the polymer in a geometric arrangement that spreads throughout the product size. Laminate Thermoset is a familiar example, based on a recognized fiber, usually categorized as a high-performance polymer composition, or a large compound because of the length of the fiber or the ribbons. In another aspect, the additive can be discontinuous (short), such as short fibres (e.g., length < 3 cm), flakes, flakes, spheres or irregulars (mm to micron size); fibres and flakes are usually in different orientations and Multiple geometric patterns are dispersed throughout the continuous matrix to form micro composites. When the platelets or in these areas have a nanoscale size as the dispersed phase fibers, in which the material is referred to as nanocomposite. They are different from micro-composites, due to that they contain many interfaces that can be used to interact with each other. Because of their unique properties, nanocomposites have a great potential for advanced applications. Composites may also be classified based on the origin (natural versus synthetic) of the matrix or filler. These are very complicated structures with continuous or dis-continuous fibers or solid particles embedded on an organic matrix that functions like knee. Fibre cellulose and lignin are a component. Bone is a composite material which consists of collagen, proteins and calcium-phosphate salts. The spider silk has organic Nano-crystals in an organic amorphous matrix. The shells of Molluscs in are made of hard mineral layers which are separated by a protein binder. A similar platy structure which provides a tortuous path for vapours and liquids can be obtained in a micro-composite which contain mica flakes infused in a synthetic thermos-set polymeric matrix.
Composites can be classified based on their intended purpose or application. For instance, someone can distinguish between two types of bio-composites. Bio-composites which are for ecological applications are a combination of natural fibres or particulates with polymer matrices from both renewable and non-renewable resources and they are characterized by the degree of their environmental degradability of the composites. Bio-composites for bio-medical applications are combinations of biostable and biodegradable polymers with inert and bioactive fillers which are intended for use in orthopaedics, regeneration of bone, or tissue engineering applications. Reinforcements that are much stronger and stiffer than the polymer mainly increase strength and the modulus. Therefore, alteration of mechanical properties may have a serious effect on the thermal expansion, transparency and stability, etc.
Continuous composites usually have long fibers or ribbon reinforcements in thermoset matrices; when they are prepared in certain geometric patterns, they can become the main component in the composite. In the case of dis-continuous composites, directional reinforcing agents namely flakes, or short fibers are compounded in a variety of directions and geometric patterns as defined by selected processing and molding methods, usually injection molding or extrusion molding. However, it should be noted that manufacturing methods for the continuous oriented fibre thermoplastic composites are available which results in very higher fibre contents, as used in the applications of high-performance engineering polymers.
Effects of Fillers/Reinforcements: Functions
Traditionally, most fillers only slightly increase the polymer modulus due to their unfavorable geometric characteristics, surface area, or surface chemical composition, whether the strength (tension, bending) does not change. Their main contribution was to lower the cost of the materials by exchanging the most expensive polymers. Another possible economic advantage was that the molding cycle was faster due to the increase in thermal conductivity and the reduction of rejected parts due to warpage. On the other hand, mould thermal expansion and shrinkage would reduce, a very common effect in most inorganic fillers. The term of reinforcing filler was created to explain discontinuous additives whose, shape or surface chemistry have been justly modified to improve the mechanical properties and strength of the polymer. The inorganic reinforcing filler is more rigid than the matrix, less deformed, causing matrix deformation, an overall reduction near the particles due to the particle matrix interface. The fibre pinches the polymer in its vicinity, decreasing the strain and increasing stiffness.
Reinforced fillers are characterized by high aspect ratios, which are defined as the ratio of length over the diameter of the fibre or the ratio of the diameter over thickness for flakes platelets. These modifications can not only improve and improve the main function of the filler (in this case use it as an average of the mechanical property), but also introduce or increase add-ons. New functions achieved by replacing or modifying existing fillers, thereby expanding the range of their use. The first group of fillers shortly after the commercialization of polypropylene included talc platelets and asbestos fibres due to their advantageous effect on heat resistance and stiffness. The search for replacement of asbestos due to health problems led to the formation of particles of calcium carbonate and mica flakes as second-generation excipients. Mica was found to be an additional operative talc to increase hardness and heat resistance while calcium carbonate was not that effective in increasing hardening but intensifying the impact strength of similar PP polymers. It has been found that the surface modification of mica with bonding agents to increase the adhesion and modification of the calcium carbonate stearate to facilitate dispersion enhances these functions and provides additional advantages such as improved workability, colour control and reduction in long-term thermal aging.
Functional Fillers, classification and Types:
The term filler is very broad and includes a very wide range of materials. We arbitrarily define as a filler a variety of solid (inorganic and organic) particulates that may be irregular, juicy or fibrous like a sheet and are used in large-scale bulk loading processes in plastics. There is a considerable variation on the chemical composition, shapes, sizes and inherent properties of various organic and inorganic compounds that are used as fillers. Typically, they are very rigid materials that are immiscible with the medium in both liquid and solid state and thus form different dispersed forms. Inorganic or organic materials can be classified as fillers and are further subdivided according to the chemical family or based on their shape and size or aspect ratio. The mainly used particulate fillers are the industrial minerals such as mica, calcium carbonate, kaolin, talc, feldspar, ash and aluminium hydroxide. The commonly used fibre fillers are glass fibers, and a variety of natural fibers have recently appeared. Carbon black has for a long time been considered a nanofiller. The latest products to enter the commercial market quickly are montmorillonite, such as montmorillonite and hydrotalcite, various oxides and nanofibers, such as single or multi-walled carbon nanotubes. Graphene sheets and halloysite nanotubes are potential additives for advanced nanocomposites; the first is a single layer of carbon atoms that are tightly packed in the honeycomb structure, and the second is produced by surface weathering of aluminosilicate minerals. Naturally occurring nanotubes. Fillers, however are multifunctional and may be categorised by a basic primary function and a plethora of additional functions.
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