Thickness of polypropylene

Unlike polyethylene, polypropylene is not crosslinked and deteriorates. The action of high-energy radiation depends in a complex way on the power, dose and wall thickness of polypropylene. Thus, it is often advised to avoid doses greater than 1 kJ/kg (0.1 Mrad). However, special grades are marketed for radiation sterilization but doses of the order of 25kJ/kg (2.5 Mrad) can lead to a certain brittleness after storage of several months. 

The influence of molecular weight of various stabilizers on the time until chalking for various wall thicknesses of polypropylene specimens [547]... 

The double-bubble process may be used to produce biaxiaHy oriented film, primarily polypropylene. In this process the first bubble formation is similar to the conventional blown film, except that the bubble is not coUapsed. Rather it is reheated to the orientation temperature and blown and drawn further in a second stage. It is then coUapsed, sUt, and wound. This process is generally limited to a final film thickness of less than 24 p.m. 

Film manufacture also requires special considerations in the case of polypropylene in order to ensure small crystal structures and hence high clarity. Chill-roll casting processes may be used and these give films of high clarity and minimal thickness variations at high rates of production. Blown film processes can, however, give superior mechanical properties and in addition equipment costs are lower, and in consequence the process is more economic for lower tonnage production. 

This is used most often in process plants. It is a tough, low-cost material with probably the widest range of chemical resistance of any of the low-cost plastics. On a volume basis, PVC is more favorable than polypropylene because the modulus of PVC is considerably higher than that of polypropylene, so it will form more rigid structures when used at the same thickness. On a weight basis it is not as favorable as PVC because it has a specific gravity of 1.4 compared with 0.92 for polypropylene. 

Example 2.1 A ball-point pen made from polypropylene has the clip design shown in Fig. 2.11. When the pen is inserted into a pocket, the clip is subjected to a deflection of 2 mm at point A. If the limiting strain in the material is to be 0.5% calculate (i) a suitable thickness, d, for the clip (ii) the initial stress in the clip when it is first inserted into the pocket and (iii) the stress in the clip when it has been in the pocket for 1 week. The creep curves in Fig. 2.5 may be used and the short-term modulus of polypropylene is 1.6 GN/m. ... 

A polypropylene pipe with an outside diameter of 80 mm is required to withstand a constant pressure of 0.5 MN/m for at least 3 years. If the density of the material is 909 kg/m and the maximum allowable strain is 1.5% estimate a suitable value for the wall thickness of the pipe. If a lower density grade of polypropylene (p = 905 kg/m ) was used under the same design conditions, would there be any weight saving per unit length of pipe ... 

If a polypropylene tank of radius, R = 0.625 m, and height 3 m is to be fllled with water for a period of one year, calculate the thickness of the tank material so that the change in its diameter will not exceed 12.5 mm. The density of the polypropylene is 904 kg/m. ... 

A cylindrical polypropylene bottle is used to store a liquid under pressure. It is designed with a 4 mm skirt around the base so that it will continue to stand upright when the base bulges under pressure. If the diameter of the bottle is 64 mm and it has a uniform wall thickness of 2.5 mm, estimate the maximum internal pressure which can be used if the container must not rock on its base after one year. Calculate also the diameter change which would occur in the bottle after one year under pressure. 

In a particular application a I m length of 80 mm diameter polypropylene pipe is subjected to two dimetrically opposite point loads. If the wall thickness of the pipe is 3 mm, what is the maximum value of the load which can be applied if the change in diameter between the loads is not to exceed 3 nun in one year. 

During the blow moulding of polypropylene bottles, the parison is extruded at a temperature of 230°C and the mould temperature is 50°C. If the wall thickness of the bottle is I mm and the bottles can be ejected at a temperature of I20°C estimate the cooling time in the mould. 

Figure 4 Light permeability of polypropylene as a function of the sample thickness 1-3-quenched polypropylene 4-6-normal polypropylene 1 and 4-100 /ac thick 2 and 5-150 jLtc thick 3 and 6-500 /jlc thick.

Mechanical strength becomes an important criterion, because wound cells (spiral-type construction), in which a layer of separator material is spirally wound between each two electrodes, are manufactured automatically at very high speed. Melt-blown polypropylene fleeces, with their excellent tensile properties, offer an interesting option. Frequently two layers of the same or different materials are used, to gain increased protection against shorts for button cells the use of three layers, even, is not unusual. Nevertheless the total thickness of the separation does not exceed 0.2 - 0.3 mm. For higher-temperature applications (up to about 60 °C) polypropylene fleeces are preferred since they offer a better chemical stability, though at lower electrolyte absorption [ 114"]. 

The micro reactor consisted of a pair of iron plates coated with Pd catalyst placed on disk-type polypropylene holders [20]. This micro channel device was encased in a stainless-steel housing. The thickness of the catalyst layer was approximately 5.0 pm 10 mg catalyst was deposited per plate, so giving 20 mg in total. The specific surface area of the catalyst was 3.6 0.4 m g ... 

Polypropylene film is found in a variety of applications. Films are thin plastic sheets with thicknesses less than 250 pm. Applications for these films include candy mappers, plastic label material, electrical capacitors (which requires very pure polymer), and fiber glass insulation backing. There are two general categories of polypropylene films unoriented and oriented. Films are manufactured through either a cast or a blown film extrusion process. Oriented films exhibit improved strength relative to unoriented films. This means that they can be... 

As the separator, microporous polypropylene film (PORP by NPO UFIM, Russia) with the thickness of 25 pm was used. 

The application of this technique to talc-reinforced polypropylene has shown that the microstructure of platelets and the resulting physical properties of the moulded composites are markedly affected [171)]. With two live feeds located at either end of the mould cavity, the talc platelets exhibited strong talc platelet alignment throughout the thickness of the moulding in the direction of the ap-... 

Fig. 10.6. Signals reflected from the top and bottom surfaces of a 40 pm thick layer of polypropylene, with the same acoustic parameters as in Fig. 10.4 (a) bonded to steel (b) unbonded, with air backing (Sinton etal. 1989).

Similarly, Plueddemann has reported [3c] an optimum silane coupling agent layer thickness of 50-200 A for commercial glass fiber treatment for use in composite materials. On the contrary, optimum adhesion of polypropylene to aluminum was obtained with a silane primer layer between 0.5 and 10 pm thick. In... 

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