Solid Phase Pressure Forming Process

Formability. Materials with a broad softening range, such as PS and PC, can be thermoformed into deep-draw package shapes. Crystalline polymers, eg, HDPE and PP, are more difficult to thermoform, but solid-phase forming processes below the melting point are possible. Multilayer semirigid barrier containers are made by Shell s Solid Phase Pressure Forming Process and the patented Dow... 

Keywords thermoforming, solid-phase pressure forming (SPPF), vacuum forming, pressure forming, processing window, viscoelasticity, residual stress, sagging, shrinkage, quality control. 

In this chart, the critical area for therraoforming is at the 44 mol percent ethylene level. At 32 mol percent ethylene, EVOH crystallizes most rapidly at 161°C. This is the ideal temperature for solid-phase pressure forming (SPPF) of polypropylene. Polypropylene is one of the more popular structural materials for EVOH resin barrier containers. EVOH resins above 38 mol percent ethylene can be formed by SPPF methods. At levels belgw 38 mol percent ethylene, melt-phase forming at temperatures above 16l c is employed. EVAL resins at 38 - 44 mol percent ethylene are specially formulated for SPPF processing. 

The exponent values in expressions (5.2)—(5.5) depend on the particular parameters in the exponent index, but they are usually much larger than the unit at r < 10-50 nm (see Table 5.1). In a homogeneous mother sys tern (free of seeds for the solid phase condensation), the process rate depends on the rate of homogeneous nucleation of the new phase from nonequilibrium (oversaturated) systems. The high partial pressure of the equilibrium vapor or solute over small particles allows the first condensed particles nuclei of the new phase) to form at a considerable oversaturation of the vapor in the initially homogeneous system. 

When a solid, such as ice, is in contact with its liquid form, such as water, at certain conditions of temperature and pressure (at 0°C and 1 atm for water), the two states of matter are in dynamic equilibrium with each other, and there is no tendency for one form of matter to change into the other form. When solid and liquid water are at equilibrium, water molecules continually leave solid ice to form liquid water, and water molecules continually leave the liquid phase to form ice. However there is no net change, because these processes occur at the same rate and so balance each other. 

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