High crystalline polypropylene

Electron microscopy shows that polymerization starts at active centres on the surface of the particle. During this initial stage, a thin polymer cover is formed on and just below the outer surface of the silica support. This thin cover consists of highly crystalline polypropylene, which acts as a diffusion barrier for the monomer. Diffusion of propylene through this layer thus becomes rate-limiting for polymer formation consequently the high initial polymerization activity decreases sharply after a few minutes and a period of relatively low activity is reached. 

HCPP high crystalline polypropylene HMWPE high-molecular-weight polyethylene... 

Diluent slurry processes for polypropylene are expensive to build and to run because of the number of pieces of equipment involved. They have largely been replaced by the more efficient bulk and gas-phase processes. Most of the remaining diluent slurry plants in the world now focus on producing speciality polymers, as diluent slurry processes do offer some advantages over other bulk and gas-phase processes. An example is the production of high-crystallinity polypropylene (HCPP), where most of the atactic polymer is dissolved in... 

HCPP High crystallinity polypropylene with isotacticity <99 %, broad MWD Chiso Corp. 

Figure 8.7 Effect of talc on plastic stiffness. , Copolymer , high crystalline polypropylene (HCPP) A, 100 homopolymer.

The stiffness of new high crystalline polypropylene polymers will be further enhanced with the addition of talc. A flexural modulus of 1 X 10 psi (6.9 GPa) or more is possible at sufficiently high talc loading. These same polymers may be used in the future at lower talc loadings, with properties similar to those ob-... 

Hassan et al. [16] studied the effect of gamma irradiation on the thermal and mechanical properties of highly crystalline polypropylene. 

The effect of gamma irradiation on the thermal characteristics of unreinforced highly crystalline polypropylene was studied by determination of melt temperature (TJ, melting enthalpy (AHJ, and degree of crystallinity values. All these values decrease with increasing radiation doses, indicating that the polymer becomes more amorphous during irradiation. 

The differential scanning calorimetric curve of highly crystalline polypropylene at various gamma radiation doses between 0 and 120 kGy indicates an increase in thermal stability of the polymer with increasing radiation dose. 

Stress-strain curves of irradiated highly crystalline polypropylene exposed to gamma rays exhibit its ductile behavior with elongation values for the nonirradiated samples up to 80%. After irradiation, highly crystalline polypropylene becomes less ductile and tensile stress decreases as well. 

It is concluded that the thermal properties (melting temperature, melting enthalpy, and degree of crystallinity), thermal stability, and mechanical properties (elastic modulus tensile strength and extension at break) of highly crystalline polypropylene showed change after irradiation. 

Fig. 2.4 DSC melting endotherms of high crystallinity polypropylene (7) crystallized frtnn the melt for 3 h at 145 °C, (2) partially melting scan (3) fully remelted after the partial melting From figure 3, Weng J, Olley RH, Bassett DC and Jaaskelainen P, Changes in the Melting Behavior with the Radial Distance in Isotactic Polypropylene Spherulites. J. Polym. Sci. Polym. Phys. 41 2342-2354. Copyright 2003 by John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc...

Lee SY, Ahn BI, Im SG, Park SY, Song HS, Kyung YJ (2004) High crystalline polypropylene microporous membrane, multi-component microporous membrane and methods for preparing the same. US Patent 6,830,849... 

Weon J-I and Sue H-J (2006) Mechanical properties of talc- and CaCOs-reinforced high-crystallinity polypropylene composites, J Mater Sci 41 2291-2300. 

It was stated that the low crystalline polypropylene (LCP) is easily oxidized than the high crystalline polypropylene (HCP). The greater degree of ordering is mirrored by the lower diffusion rate. For example, the final content of ketones in LCP after 21 days with the irradiance of 14,000 kJ m exceeds with 25 % the similarly degraded HCP, while acid content is more abundant in LCP with about 57 % than it was accumulated in HCP [70]. 

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