Single phase plastics

Random copolymers (single phase plastics) homogenous amorphous phase... 

The compatibility is also a very important fact. Good compatibility means that the two kinds of polymers in the blends are mixed at the molecular level to form an apparently single phase. This kind of blending system shows only one Tg. If the two polymers have only partial compatibility, the entire system will maintain two different TgS and TPU only serves as a modifier not a plasticizer. 

Plasticizers and catalysts can be mixed into the liquid curative prior to addition to the prepolymer if required. They must be well blended so that there is a uniform mix. The correct weight of the curative or blend must be accurately weighed in a clean, dry container or with great care directly into the prepolymer. The material must be added in a thin, continuous stream that will form a single phase. The addition must be done rapidly. 

The aim of this Chapter is the development of an uniform model for predicting diffusion coefficients in gases and condensed phases, including plastic materials. The starting point is a macroscopic system of identical particles (molecules or atoms) in the critical state. At and above the critical temperature, Tc, the system has a single phase which is, by definition, a gas or supercritical fluid. The critical temperature is a measure of the intensity of interactions between the particles of the system and consequently is a function of the mass and structure of a particle. The derivation of equations for self-diffusion coefficients begins with the gaseous state at pressures p below the critical pressure pc. A reference state of a hypothetical gas will be defined, for which the unit value D = 1 m2/s is obtained at p = 1 Pa and a reference temperature, Tr. Only two specific parameters, Tc, and the critical molar volume, VL, of the mono-... 

However, the single-phase epoxy nitrile adhesive achieves its high peel strength by bulk elongation. Other properties, such as heat and chemical resistance, are generally degraded as they are when other flexibilizers or plasticizers are added to the epoxy. The two-phase version of this adhesive hybrid solves many of these problems. 

Sintered silicon carbides are formed by all the traditional methods as well as standard plastic forming techniques such as injection molding. These compacts are sintered with small amounts of additives at very high temperatures in inert atmospheres to form essentially a single phase silicon carbide structure. 

Assuming single phase is retained on plasticization, equations derived for random polymers can be used... 

The formation of a periodic microstructuie due to eutectic crystallization allows significant enhancement of the strength and deformation before fracture as compared to single-phase material. In this case, high values of the modulus of elasticity are obtained, micro-plastic deformation in bending tests appears, and the eutectic character of alloys ensures their high casting properties. 

In their processible mixture, these one-component products, also belonging to physically setting adhesives, consist of two components PVC (polyvinyl chloride-) particles and plasticizers (Section 9.2.9). The solid PVC particles are disperged in the high-viscosity plasticizer. The adhesive layer formation occurs by heating (120-180 °C), when the thermoplastic PVC swells and is thus able to absorb the plasticizer (no chemical reaction ). This process is called a sol-gel process. The formerly two-phase system (sol) is turned into a single-phase system (gel) by the inclusion of the plasticizer. 

In addition, the polymer blends segment of the plastics industry increases at about three times faster than the whole plastics industry. Blending has been recognized as the most versatile, economic method to produce materials able to satisfy complex demands for performance. By the year 2000 the world market for polymer blends is expected to reach 51 million tons per annum, worth well over US 200 billion. The tendency is to offer blends that can be treated as any other resin on the market hence their processability must closely match that of single-phase polymer, but offer a much greater range of performance possibilities. 

Figure 12. Tensile strength and plastic deformability as a function of temperature for single-phase, polycrystalline,...

Figure 15. Tensile strength, i.e., fracture stress, ultimate tensile strength (UTS), 0.2% yield stress, and plastic deformability, i.e., tensile elongation, as a function of temperature for single-phase, polycrystalline TiAl with 54 at.% Al (Lipsitt et al., 1975).

Miscible blends of elastomers differ from corresponding blends of thermoplastics in two important areas. First, the need for elastic properties requires elastomers to be high molecular weight. This reduces both the kinetic rate and the thermodynamic driving force for the interdiffusion and thus formation of a miscible single phase of dissimilar elastomers. Second, elastomers are plasticized in conventional compounding with process oils. The presence of plasticizers leads to both a higher free volume for the blend components and a decrease of the endothermal interactions. 

When the temperature of the system increases, incompatibility decreases and the system becomes a single-phase system at temperature Tao- The temperature of this transition may vary depending on the system composition and it reaches its maximum at some point Tj ,. Above Tjj, called the upper critical solution temperature, UCST, both components are compatible in any proportion. The diagrams of polymer-plasticizer blends differ from dia-... 

Note that all of the above eqnations assnme that the polymer-plasticizer system is a single-phase system in a whole range of concentrations. If the compatibility is limited, it is necessary to expect that, at the plasticizer concentration greater than the compatibility limit, the glass transition temperatnre of polymer phase may not vaiy on inctease of plasticizer fraction." That is the concentration dependence of ATg can be described by one of the eqnations (10.13-10.22, 10.24-10.26) only np to the compatibility limit. Outside the compatibihty hmit the glass transition temperature is nearly constant (see Figure 10.34, curve 2). This corresponds to Kanig s inconsistency discussed above. In the case of the weak compatibility these equations may be used only within rather narrow intervals of plasticizer concentrations. 

The traditional views on plasticization of polymers are based on results of studying the single phase polymer systems and microheterogeneous polymers which have the same chemical stmctures of hard and soft phases. 

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