Polymer materials modifications

V.N. Kestelman. Physical Methods of Polymer Materials Modification. Moscow, Khimia, 1980. 

The real breakthrough came when chemists developed processes for making large molecules from their smallest units. Instead of the ten or so natural polymers and modifications of them, the engineer was suddenly presented with hundreds of new materials with remarkable and diverse properties. The number is still increasing. 

These observations demonstrate that the different functional groups can be attached to the aromatic ring of PS with various chemical modification conditions, and it is possible to obtain different technical properties for polymer materials. 

Biomass is a relatively inexpensive raw material. Since it is made by nature there is an enormous saving of energy. The main research areas include (1) isolation and purification of natural monomers and polymers, (2) modification of natural monomers and polymers, and... 

Molecular hybrids between organic polymers and silica gel are expected to show many possibilities as new composite materials. First, the hybrids may show intermediate properties between plastics and glasses (ceramics). In addition, the composition of the hybrids can be widely varied. In other words, the hybrids can be used to modify the organic polymer materials or to modify the inorganic glassy materials. The hydrophilic modification as described before is a typical example. 

Radiation-induced modification or processing of a polymer is a relatively sophisticated method than conventional thermal and chemical processes. The radiation-induced changes in polymer materials such as plastics or elastomers provide some desirable combinations of physical and chemical properties in the end product. Radiation can be applied to various industrial processes involving polymerization, cross-linking, graft copolymerization, curing of paints and coatings, etc. 

A kinetic model based on the Flory principle is referred to as the ideal model. Up to now this model by virtue of its simplicity, has been widely used to treat experimental data and to carry out engineering calculations when designing advanced polymer materials. However, strong experimental evidence for the violation of the Flory principle is currently available from the study of a number of processes of the synthesis and chemical modification of polymers. Possible reasons for such a violation may be connected with either chemical or physical factors. The first has been scrutinized both theoretically and experimentally, but this is not the case for the second among which are thermodynamic and diffusion factors. In this review we by no means pretend to cover all theoretical works in which these factors have been taken into account at the stage of formulating physicochemical models of the process... 

Development of new applications of radiation modifications of the properties of polymers in high technology industries such as electronics and the exposure of polymer materials to radiation environments as diverse as medical sterilization and the Van Allen belts of space have resulted in a renewed interest in fundamental radiation chemistry of polymers. 

The fact that unstable P.B.15 types tolerate less than 200°C is a disadvantage in the coloration of plastics. With increasing temperature, the pigment frequently converts to the [l-modification, a tendency which is especially pronounced in polymer materials which contain aromatic rings, such as polystyrene, ABS, or PETP. 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

Most recently, significant research efforts have been focused on materials compatibility and adhesion at the zeoHte/polymer interface of the mixed-matrix membranes in order to achieve enhanced separation property relative to their corresponding polymer membranes. Modification of the surface of the zeolite particles or modification of the polymer chains to improve the interfacial adhesion provide new opportunity for making successful zeolite/polymer mixed-matrix membranes with significantly improved separation performance. 

As already mentioned, the results and rules found in dependencies of properties with the morphology of polymeric materials are in most cases limited to special classes of polymers or even one polymer species only. Therefore, the intention of this subsection can only be to demonstrate the potential and the possibilities which exist to influence the properties of polymers by modification of their morphology. This will be done with relevant examples that are described in detail in Chaps. 2-5. 

Chemical analysis of polymer materials is difficult because of the large number and types of such materials and because of modification and compounding practices of conventional polymers. 

As mentioned, polymer hybrids based on POs are effective as a compati-bilizer between the olefinic materials and polar ones. Furthermore, some polymer hybrids, such as PP-g-PMMA, etc., show good mechanical strength as polymer materials. On the other hand, surface modification of the molded polymer is one of the most attractive methods to let polyolefin materials functionalize. In this sense, surface polymerization of functional monomers on polyolefins is an important subject for polyolefin hybrids. As previously referred to, the growth of PS on PP via the RAFT process has been reported [92]. 

Marosi, G., Anna, P., Bertalan, G., Szabo, S., Ravadits, I., and Papp, J. 2001. Role of interface modification in flame retarded multiphase polyolefin systems. In Fire and Polymers Materials and Solutions for Hazard Prevention, Vol. 797. eds. Nelson, G. and Wilkie, C. Washington, DC American Chemical Society, pp. 161-71. 

PhotoDecomposition (APD) that occurs above a well-defined ablation threshold usually leads to removal of polymer material leaving a new fresh "clean" surface with the same composition as the untreated material. However, in the case of PET (JL) both composition and structural modifications occur even for fluences below the ablation threshold. 

Polymer surfaces are modified to obtain the desired surface properties without altering the bulk properties (J ). One of the most desired properties is adhesion between polymers and other materials such as polymers, metals or ceramics (2). There are many techniques for polymer surface modification, but they can be divided into two major categories. One is a dry process in which the polymers are modified with vapor-phase reactive species that are... 

Physical or chemical modification methods have been employed to increase the toughness of polymer materials. The chemical modifications include random copolymerization, block copolymerization, grafting, etc. the physical ones include blending, reinforcing, filling, interpenetrating networks etc. [24-26]. 

Plasma treatment is widely used commercially for polymer surface modification. Plasma discharge treatments are used to improve adhesiveness and printing properties, to improve cell adhesion to tissue culture substrates (1 ) and to etch or clean the surfaces of materials (removal of photoresist materials on semiconductors, for example ( ). The surface characterization of plasma-modified surfaces is important in order to provide greater insight into how the properties are changed. 

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