Polypropylene processing conditions

Isotactic polypropylene exhibits four crystalline structures alpha, beta, gamma and mesomorphic. Each of these structures forms under specific processing conditions and defines the properties of the polypropylene. In polypropylene containing the alpha, beta, and gamma... 

Compositions and processing conditions are disclosed for the production by rotomoulding of polypropylene foams, hitherto satisfactorily produced only by injection... 

Carbon dioxide gas was used as a physical blowing agent to produce medium density polypropylene foam sheets using a single screw extruder. The mechanical properties of the foam were similar in the machine direction and in the transverse direction. Abetter surface finish and a lower density was produced by using a commercial wrapping film as a cap layer. The process conditions and the die design data are presented and an attempt made to relate them to the product characteristics. 4 refs. 

Meh Spinning. This process is used to produce a broad range of polypropylene fibers ranging from fine, dtex (one denier) staple coarse continuous filaments. Hoiuopolyiners are almost exclusive used to produce fibers, although copolymer blends are used in some special applications. Processing conditions and polymer melt flow vary with the desired fiber type. 

Polypropylene (PP), on the other hand, undergoes predominantly chain scission under all processing conditions [7, 8, 9, 10, 11] with associated reduction in the molar mass and melt viscosity (see Scheme 3). The propagation reaction (Scheme 1, reaction 3) in PP is particularly facilitated by intramolecular hydrogen abstraction leading to the formation of adjacent hydroperoxides along the polymer chain that are less stable than isolated hydroperoxides and lead to an increased rate of initiation. 

A simplification of stabilizer systems for polypropylene would be desirable. The ideal situation, of course, would be to have one inexpensive additive which could protect polypropylene to such a degree that a single resin could be used across the board, regardless of processing conditions or final application. This does not seem likely, however, because of the complexity of polypropylene degradation mechanisms which take place under various exposure conditions. 

Among the three known crystalline structures (a, j3, y) of isotactic polypropylene (PP), the -modification is certainly the most fascinating one. While the stable a-structure develops under standard process conditions, the occurrence of the /J-form has to be forced (i) by directional crystallization in a temperature gradient field [1-3] (ii) by shear-induced crystallization [4-12] or (iii) by the addition of specific nucleating agents [13-31]. This latter technique is preferred at the industrial scale. 

Plastics. Plastics are the polymeric materials with properties intermediate between elastomers and fibers. In spite of the possible differences in chemical structure, the demarcation between fibers and plastics may sometimes be blurred. Polymers such as polypropylene and polyamides can be used as fibers and plastics by a proper choice of processing conditions. Plastics can be extruded as sheets or pipes, painted on surfaces, or molded to form countless objects. A typical commercial plastic resin may contain two or more polymers in addition to various additives and fillers. Additives and fillers are used to improve some property such as the processability, thermal or environmental stability, and mechanical properties of the final product. 

Table I. Processing Conditions and Properties of Microporous ACCUREL Polypropylene Membranes...

Product-wise, the versatility of the Spherizone process is demonstrated by the high-quality product range that includes all standard polypropylene grades, as well as many unique, special products. One key to this versatility is, as mentioned above, the unique design and operation of the MZCR, which, with a very broad range of feasible process conditions, allows for many kinds of polymer structures as well as intimately mixed polymer compositions to be produced. 

The last example shows that it is also feasible to use SLMs to remove and recover efficiently radioactive metals from nuclear process effluent. By using a microporous hydrophobic polypropylene hoUow-fiber supported Hquid membrane (HFSLM) consisting of extractant, tri-w-butyl phosphate (TBP) as carrier diluted with w-dodecane, actinides such as uranium (U) and plutonium (Pu) were removed [188]. It was concluded after modeling and evaluation of the process conditions that it is possible to remove more than 99% of U(VI) and Pu(IV) from process effluent in the presence of fission products when stripping reagent 0.1 M hydroxylamine hydrochloride in... 

To study cooling rate effects which might affect the supramolecular self-assembly of trisamides in i-PP, we investigated the influence of the processing conditions on the electret performance. Isotactic polypropylene containing 0.09 wt% of compound 1 was chosen for these experiments. After compression molding, the films... 

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. 

Pyrolysis and reforming of several types of common plastics (polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polyurethane, and polycarbonate) were studied qualitatively, using a micro-reactor interfaced with a MBMS. Each type of plastic pyrolyzed at 550-750°C. This was followed by steam reforming of vapors in a fixed bed of C-11 NK catalyst at 750-800°C. The composition of the product gas (mass spectrum) was observed for different values of the steam-to-carbon mtio and space velocity that changed depending on the size of plastic samples. Preliminary tests showed that at process conditions similar to those used for reforming natural gas, polymers were almost completely converted to hydrogen and carbon oxides. 

Table 11.44. Processing conditions of polypropylene-based blends [Rolando and Krueger, 1992]...

An important factor with thermoforming is that the polymer should show a pronounced rubbery region on the temperature scale. For this reason, amorphous polymers such as PVC, PS, poly(methyl methacrylate) (PMMA), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), etc. are well suited for thermo forming. With semicrystalline polymers, the rubbery region is largely masked by the crystallinity (Fig. 23.19). With PE and polypropylene (PP), thermoforming is, therefore, a critical operation, in which the processing conditions should be very carefully controlled. 

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