HEAT SHRINKAGE

In the labeling market, hot melts provide the capability to bond non-porous films to plastic cans and bottles. Hot melt usage has grown with the prevalence of such plastic to plastic laminations. The choice of hot melts depends on the equipment, the substrates, whether the bottles are filled or unfilled, and any post-labeling processing (e.g. pasteurization, or heat shrinkage of the film). 

FIGURE 31.15 Variation of percent heat shrinkage and amnesia rating with radiation doses of low-density polyethylene/ethylene-vinyl acetate (LDPE/EVA) film from 50 50 blend without ditrimethylol propane tetra-crylate (DTMPTA). (From Chattopadhyay, S., Chaki, T.K., and Bhowmick, A.K., Radiat. Phys. Chem., 59, 501, 2000. With permission.)... 

Heat durability and Heat Shrinkage of Yams, Du Pont Bull. (1959)... 

While PLA has made good progress in flexible film applications, development of new technologies is required to improve the fundamental qualities such as thermal properties heat resistance, heat shrinkage etc.) and mechanical properties (strength, ductility, etc.) for further successful commercialisation. 

Warping - Dimensional distortion or deviation from the intended shape of a plastic or rubber article as a result of nonuniform internal stress, e g., caused by uneven heat shrinkage. Also called... 

Eilm RT N. e-, 30-100 Peroxide Heat shrinkage, haze, shrinkage temperature, shrinkage tension, tensile strength, elongation, impact strength 66... 

Russian State Standard 25951-83. Polyethylene Heat-Shrinkage Film. Technical Specifications. 

For prediction of mold filling and flow-through dies, computer modelling is increasingly used. In addition to viscosity, measurements may be needed for specific heat, shrinkage, thermal conductivity, and pressure- volume -temperature (PVT) relationship. A differential scanning calorimeter (DSC) can be used for specific heal measurements. 

For industrial use, high-tenacity yarns, such as the tire cord, have to be drawn under conditions where low heat shrinkage, low extension, and high modulus products are produced. In fact, a tire cord is a highly specialized product, and complete integrated continuous polymerization spiiming and drawing plants (cp-spin-draw) have been developed. The process is little discussed in the open literature and the reader is directed to the patents of DuPont, Fiber Industries, and Allied Chemical Corporation (none of these companies currently exist as fiber producers). 

The superdrawn filaments were very resistant to heat shrinkage, as seen in Figure 3.63. Mechanical property measurements on these filaments after the heat shrinkage showed a 16% loss in modulus and a 10% loss in tensile strength. The fibers began to melt at 155°C, and the peak maximum occurred at 161°C. 

Ube-Nitto Chemical Products, Japan, has also developed a high-strength (HS) polypropylene fiber under the brand name Simtex. The technology is principally to optimize the crystallization of fiber by a new orientation technique. The HS fiber exhibits strength up to 88-115 cN/tex versus 40 60 cN/tex for the conventional polypropylene fiber. The heat shrinkage rate is below 50%. It also has high chemical resistance, especially to organic... 

The dimensional stabUity of synthetic yarns and textiles can be considerably enhanced by a thermosetting process, i.e. heat treatment under dry heat, steam or hot water. Thermosetting may be undertaken either with or without applied tension. Thermally treated filament yarns and staple fibres show less heat shrinkage, have a reduced tendency to crimp and show improved recovery from creasing. 

The relaxation of the segmental orientation and the chain extension in polycarbonate (Makrolon 1143 from Bayer AG) were studied by IR dichroism and heat shrinkage after a step strain deformation to a draw ratio of 1.75. This makes it possible to distinguish between local relaxation mechanisms (Rouse) and large-scale relaxation... 

Filter fabrics Low heat shrinkage 1 7 Tape width 1.0/2.0... 

Several general disadvantages of bulk polymerization (removal of the reaction heat, shrinkage, nonsolubility of the resulting polymer in the monomer, side reactions in highly viscous systems such as the Trommsdorff effect or chain transfer with polymer) are responsible for the fact that many polymerization processes are carried out in the presence of a solvent. A homogeneous polymerization occurs when both monomer and polymer are soluble in the solvent. When the polymer is insoluble in the solvent, the process is defined as solution precipitation polymerization. Other heterogeneous polymerization reactions in liquid-solid or liquid-liquid systems such as suspension or emulsion polymerizations are described later. Conventional solution polymerization is compared with solution precipitation polymerization for the synthesis of acrylic resins in Ref. [34]. 

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