Plastics multiphase polymer

Since then the research activity may even have increased. Central themes were the molecular mechanisms in craze initiation, the influence of molecular weight and presence of entanglements, the nature of plastic instabilities, the role of crazes as precursors to cracks, and last but certainly not least, the formation of crazes in semicrystalline and multiphase polymers. Although considerable progress has been made in the above mentioned fields, some important questions are still open today. 

Faflure in multiphase polymers and polymer composites (non-fibrous) is reviewed by Professor Bucknall. Several examples are presented in which the effect of adding a dispersed second phase to a polymer can be either beneficial or deleterious to stress, strain, or work to break. It is shown that two basic modes of local plastic deformation may be operative, namely crazing and shear band formation. 

OUGHENED PLASTICS ARE USUALLY MULTIPHASE POLYMERS the dispersed... 

It is well known that the main mechanisms of inelastic deformation are shear yielding and multiple crazing in the rigid matrix phase, as well as cavitation in the soft dispersed phase in rubber-toughened plastics and multiphase polymers [42]. Eor many years, these mechanisms have been studied using microscopy techniques. 

Adhesion of thermodynamically incompatible polymers is of current interest because of its implications for developing new multiphase polymer materials and for recycling of mixed plastic wastes. Many elegant experiments have been reported in which various types of copolymer are introduced at the interface as putative compatibilizers. The interface may be strengthened as a result of interdiffusion and roughening on a nanoscale. 

In the last two decades, numerous experimental and theoretical studies dealing with reaction-induced phase separation in multiphase polymer systems (mostly porous matrices, toughened plastics, melt processable thermoplastics [143], molecular composites, polymer dispersed liquid crystals, etc.) have been reported. A newcomer in this field should get acquainted with hundreds (possibly thousands) of papers and patents. The intention of this review was to provide a qualitative basis (quantitative occasionally) to rationalize the various factors that must be taken into account to obtain desired morphologies. 

It is generally accepted that growth in plastics consumption and the development of new and specialized applications are related to advances in the field of multicomponent, multiphase polymer systems. These include composites, blends and alloys and foams. Fillers are essential components of multiphase composite structures they usually form the minor dispersed phase in a polymeric matrix. 

Multiphase polymers are commonly toughened plastics which contain a soft, elastomeric or rubbery component in a hard glassy matrix or in a thermoplastic matrix. An example of the typical brittle fracture morphology of an unmodified thermoplastic is shown by SEM of nylon (Fig. 5.45A). Addition of an elastomeric phase modifies the brittle fracture behavior of the matrix, as shown in a fracture surface of a modified nylon (Fig. 5.45B). The modification depends on the composition and deformation mechanism of the material [204, 215], but normally it increases the fracture toughness and strength from that of the unmodified matrix resin. Impact strength, as measured for instance by an Izod impact testing apparatus, is affected by the dispersed phase... 

There are multiphase polymers where OM and SEM techniques cannot fully describe the microstructure due to a combination of small particle size (less than 0.5 /xm) and good adhesion between the dispersed phase and the matrix. Additionally, broad particle size distributions are often encountered, and in these cases a combination of techniques is required to describe the microstructure. TEM requires ultrathin specimens, about 50-500 nm or less in thickness, which are prepared by film casting or ultrathin sectioning. Films formed by casting or dipping methods provide a much easier specimen preparation method than ultrathin sectioning of bulk plastics. However, a major question in such studies is always whether the microstructure is the same as in bulk polymers of industrial interest. Specific stains are often required to provide contrast between the dispersed phase and the matrix pol)m[ier. 

As in the case of emulsion polymerization, particle morphology is ruled by the interplay between thermodynamics and kinetics. Equilibrium morphologies are reached when the internal viscosity of the polymer particle is low. Thus, due to the plasticizing effect of the alkyd resin, equilibrium morphologies are usually reached for alkyd/acrylic systems [96]. The equilibrium morphology is affected by the presence of graft copolymer that reduces the interfacial tension between the polymer phases in the particle. Methods to calculate the equilibrium morphology of multiphase polymer particles are available [43]. 

Styrenic block copolymer (SBS) TPEs are multiphase compositions in which the phases are chemically bonded by block copolymerization (see chapter Introduction to Plastics and Polymers). At least one of the phases is a hard styrenic polymer. This styrenic phase may become fluid when the TPE composition is heated. Another phase is a softer elastomeric material that is rubber-like at room temperature. The polystyrene blocks act as cross-links, tying the elastomeric chains together in a three-dimensional network. SBS TPEs have no commercial applications when the product is just a pure polymer. They must be compounded with other polymers, oils, fillers, and additives to have any commercial value. 

Dae Han C, Kim JK (1993) On the use of time-temperature superposition in multicomponent/ multiphase polymer systems. Polymer 34 2533-2539 De Geimes PG, Prost J (1993) The physics of liquid crystal. Clarendon, Oxford Dealy J, Wissbum K (1990) Melt rheology and its role in plastics processing. Van Nostrand Reinhold, New York... 

Further results of all-atom molecular dynamics simulations have also been reported for PEO/PMMA blends [214], POSS/PE blends [215], blends of hydroxyl-terminated polybutadiene with explosive plasticizers [217], as well as a novel force field for PDMS and mixtures with alkanes [216]. The simulation of multiphase polymer systems has also been reviewed [208]. 

When analyzing multiphase samples, it may be possible to detect several glass transitions in a DMA measurement as was the case in the thermal characterization of multiphase polymer films described above. DMA is also able to provide information on the effects of plasticizers, resins and fillers on the polymer fihn. 

The world production of plastics in 1995 is projected at 76 million metric tons (mT) with an annual growth rate (AGR) of 3.7%. The expected AGR of PBAs is 12% and that of composites 16%. In 1987, 21% of polymers were used in blends and 29% in composites and filled plastics [56]. If this trend continues, by 1995 all manufactured resins will be used in multiphase polymeric systems. Two factors moderating the tendency are ... 

Martin, O. and Averous, L. 2001. Polyjlactic add) Plasticization and properties of biodegradable multiphase system. Polymer 42 6209-6219. 

The heat resistance of ABS can be improved by adding a high- Tg polymer, by chemically modifying the SAN copolymer, or by removing low molecular weight plasticizers. This review will not cover the multiphase blend approach, exemplified by extruded mixtures of polycarbonate and ABS. The focus will concentrate on the chemical modification of ABS by the use of a different, continuous-phase styrenic copolymer. 

In multiphase systems, like in rubber modified plastics, stabilizers can partition between different phases of the system [37]. The actual stabilizer concentration in either elastomer or thermopl tic phases may differ very significantly from the average stabilizer concentration declared for the whole multiphase system. In polymers like ABS, the partitioning of stabilizers may exert a controlling influence on the final stabilization effect. A proper chemical modification of the stabilizer molecule can enhance its affinity to a phase of the multiphase system which is more sensitive to degradation. 

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