Polymer Compounding Formulations and Techniques

Prior to polymerisation and the conversion to a finished product, polymer raw materials normally need to go through a compounding stage. In compounding, the polymer is modified physically and chemically by additives that change its properties. 

The general purpose of compounding is to impart the physical properties required to the end product and simultaneously transform the polymer melt into powder, beads or flakes, pellets, or granules to be further processed, handled or stored. 

These are carried out either individually or in combination with each other by compounding extruders of various designs and with various methods of operation. 

The production and applications of polymers have gradually developed, gaining ground in many fields. The main classes of polymers, namely polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene and polyethylene terephthalate are produced in millions of tonnes annually [1]. There are many methods of polymer synthesis free-radical polymerisation (bulk, solution, emulsion and suspension), condensation polymerisation, ethoxylation, polymer compounding and formulations involving solvents, fillers, pigments and so on. Besides the high volume consumption of these common plastics, the demand for polymers with specific end-use properties has increased. 

Polymer compounding provides the opportunity for a unique combination of very high chemical and thermal stability allied with the ability or promise of forming useful materials. Compounding is a process to reduce non-uniformity of composition. It is achieved in the extruder by inducing relative motion of the material. Molecular diffusion and turbulent motion are essentially limited to low viscosity liquids. 

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Nanocapsules can be formulated from a variety of synthetic or natural monomers or polymers by using different techniques in order to fulfil the requirements of various applications. Both, hydrophobic and hydrophilic liquids are of high interest for encapsulation. So, e.g., either sensitive or volatile substances, as drugs or fragrances have to be encapsulated and protected for applications with a sustained demand of the respective compound. DNA, proteins, peptides or other active substances can be encapsulated in order to target them to specific cells. A further benefit of the polymeric shell is the possibility to control the release from the composite particles and hence the concentration in the environment. 

Measurements of electrode impedance offer an extra bonus an electrode placed in an ionic solution is surrounded by the electrical double layer having the corresponding double-layer capacity that contributes to the overall electrode impedance. The value of the double-layer capacity sensitively reflects the interfacial properties of substances present in the solution and therefore the impedance technique is suitable for the investigation of adsorption at the interface, the phase transition in monolayers, the interaction of biosurfactants with counter ions, the inhibition properties of polymers, the analysis of electro-inactive compounds on the basis of adsoprtion effects, and other topics. The theory of electrode impedance has been well formulated and a complete set of diagnostic criteria for the elucidation of electrochemical processes is available. With the increasing availability of ready-made instrumentation an increased number of applications in biochemical studies is also to be expected. 

Analytical techniques used in troubleshooting and formulation experimentation available to the rubber compounder were reviewed [90]. Various textbooks deal with the analysis of rubber and rubber-like polymers [10,38,91]. Forrest [38] has illustrated the use of wet chemistry, spectroscopic, chromatographic, thermal, elemental and microscopy techniques in rubber analysis. 

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