Processing polypropylene, effect

Molecular features of polypropylene Expected process/product effects Potential application... 

During processing polypropylene melts under the action of transverse strain there occur strain-chemical conversions which can result in both decrease and increase in their molecular masses the mechanical effect on the rapidity and level of the occurring processes is considerably more prominent than the mere contribution of thermal and thermal-oxidative breakdown. These data necessitate studying the process of polymer destruction. For this purpose it would be most effective to apply the criterion of assessment of the intensity with which destructive processes happen in polymer melts. 

Iring, M. Tudos, F. Thermal oxidation of poly-ethylenes and polypropylene effects of chemical structure and reaction conditions on the oxidation process. Prog. Polym. Sci. 1990, 15 (2), 217-262. 

S. Chmela, D.J. Carlsson, and D.M. Wiles, Photo-stabilizing efficiency of IV-substituted hindered amines in polypropylene effects of processing conditions and exposure to a protonic acid, Polym. Degrad. Stab. 1989, 26, 185-195. 

Bettini, S.H.R. and AgneUi, J.A.M. 1999. Grafting of maleic anhydride onto polypropylene by reactive processing. I. Effect of maleic anhydride and peroxide concentrations on the reaction. J Appl Polym Sci. 

Phillips, R., Herbert, G., News, J. and Wolkowicz, M. (1994) High modulus polypropylene Effect of polymer and processing variables on morphology and properties. Polymer Engng Sci., 34,1731-43. 

Knappe and Kress investigated the influence of repeated injection molding on the mechanical properties of samples for many different thermoplastics (Table 2.6) [32]. Similar experiments have also been performed by Shishova [33] and by Akutin and their co-workers [34] on polypropylene and polycarbonate, respectively, where decreases in tensile properties were found with repeated processing. Similar effects have also been reported during mixing of polyolefin melts in different equipment [30]. 

Iring, M., Tiidos, F. Thermal Oxidation of Polyethylene and Polypropylene Effects of Chemical Structure and Reaction Conditions on the Oxidation Process, Progress in Polymer Science, 15 (1990) 2, p. 217-262... 

EP 0 455 211 B2 (European Patent). C Gruner, C de Oliveira Santos. Process of effect-coating of polypropylene substrates. April 30, 1991. 

Foi example, nylon pile fabrics, exhibiting higher moisture regain, have different traction characteristics under wet and dry conditions than do polypropylene-based materials. Effects of artificial turf fabric constmction on shoe traction ate given in Table 2. Especially effective in aiding fabric surface uniformity is texturing of the pile ribbon, a process available for the two principal pile materials nylon and polypropylene. 

The important beneficial effects that substrate roughness can bring were firmly established in the late sixties and early seventies, principally as a result of work in two areas. The first was associated with the electroless deposition of metals onto plastics such as ABS and polypropylene. In the process the plastics must be etched in a way which produces pits on a micrometre scale. Such a topography had been shown to be a necessary, but not sufficient condition for adequate adhesion [40]. 

From this relatively simple test, therefore, it is possible to obtain complete flow data on the material as shown in Fig. 5.3. Note that shear rates similar to those experienced in processing equipment can be achieved. Variations in melt temperature and hypostatic pressure also have an effect on the shear and tensile viscosities of the melt. An increase in temperature causes a decrease in viscosity and an increase in hydrostatic pressure causes an increase in viscosity. Topically, for low density polyethlyene an increase in temperature of 40°C causes a vertical shift of the viscosity curve by a factor of about 3. Since the plastic will be subjected to a temperature rise when it is forced through the die, it is usually worthwhile to check (by means of Equation 5.64) whether or not this is signiflcant. Fig. 5.2 shows the effect of temperature on the viscosity of polypropylene. 

In preliminary tests, melt mixed blends of PP and LCP were processed at six different temperatures (Tcyi 230, 240, 250, 260, 270, and 280°C) with a Brabender Plasti-Corder PLE 651 laboratory single-screw extruder. The measured melt temperatures were about 10°C higher than the cylinder temperatures (Tcyi). The objective was to study the influence of temperature on the size and shape of the dispersed LCP phase. Two different polypropylenes were used to ascertain the effect of the viscosity of the matrix on the final morphology. Different draw ratios were obtained by varying the speed of the take-up machine. 

In solution polymerization, monomers mix and react while dissolved in a suitable solvent or a liquid monomer under high pressure (as in the case of the manufacture of polypropylene). The solvent dilutes the monomers which helps control the polymerization rate through concentration effects. The solvent also acts as a heat sink and heat transfer agent which helps cool the locale in which polymerization occurs. A drawback to solution processes is that the solvent can sometimes be incorporated into the growing chain if it participates in a chain transfer reaction. Polymer engineers optimize the solvent to avoid this effect. An example of a polymer made via solution polymerization is poly(tetrafluoroethylene), which is better knoivn by its trade name Teflon . This commonly used commercial polymer utilizes water as the solvent during the polymerization process,... 

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