PARTIAL MELTING AND RECRYSTALLIZATION OF ISOTACTIC POLYPROPYLENE

A relatively high predetermined crystallization temperature （135℃） was chosen to grow well developed iPP spherulites, then the partial melting was carried out at a temperature of 165℃, where the preformed spherulites were seen to only decrease their size but not completely melted. The crystallization behavior of partially melted isotactic polypropylene （iPP） has been carefully examined by different scanning calorimetry （DSC） and polarized light microscopy （PLM）. The experimental results show that at a special annealing temperature （165℃） the melting behavior of iPP includes two parts with different mechanism, one part is the melting of iPP spherulite outside, another is the partial lamellae perfection during longer annealing time in the unmelted spherulite. The conformational orders of the iPP melt decrease with the increase of the annealing temperature.

HOT DEFORMATION AND MARTENSITIC TRANSFORMATION BEHAVIORS OF Fe-32%Ni ALLOY

The Hot deformation and martensitic transformation behaviors of Fe-32%Ni alloy was investigated by measurements of electrical resistance and X-ray diffraction. With the increase in strain, the austenite goes through from the work-hardened to the partial dynamcally re-crystallized and then to the completed dynamically re-crystallized. The martensitic transformation characteristics depend on the austenite states. The work-hardening in small strain is helpful to martensitic transformation due to the low dislocation density and little lattice distortion, while the high dislocation density and severe lattice distortion by the increase in strain will hinder the martensitic nucleation. Once dynamic re-crystallization （ DRX ） takes place, the martensitic transformation will be enhanced again, which is related to the heterogeneous dynamic substructures. The growing DRX grain can enhance the martensitic nucleation due to the low dislocation density near its grain boundary.

THE EFFECT OF EC ON ORIENTATION AND RELAXATION OF PP OBTAINED VIA DYNAMIC PACKING INJECTION MOLDING

Abstract As a long term project aiming at engineering plastics based on polypropylene(PP),in this work,we report theeffect of ethylene-cellulose(EC)on the orientation and relaxation of PP obtained via dynamic packing injection molding(DPIM).2d-WAXD results showed that PP with a highly oriented structure and a shish-kebab structure were achieved byDIPM,leading to an increase of tensile strength from 35.0 MPa to 48.6 MPa.The degree of orientation of PP was increasedby adding only 1% of EC,resulting in a further increase of tensile strength from 48.6 MPa to 53.8 MPa.Shish wasfound to exist not only in the oriented layer but also in the core of the sample after adding EC,as evidenced by DSC result.This was understood as due to the overall decrease of viscosity by the addition of EC,thus an increasing of shear rate.Highershear rate can favor the orientation of molecules and continuous growth of shish structure,resulting in a change ofshish distribution along the sample thickness.On the other hand,the relaxation mode of shish in the melt re-crystallization of PP is also greatly affected by the presence of EC.A retarded relaxation of PP macromolecules was seen.Even more.SEM results showed that EC could form the short fibers in PP matrix along the shear flow direction.Comparedwith the morphology obtained by conventional injection molding,a much better dispersion and easy break-up of EC in PPmatrix were observed for samples obtained by dynamic packing injection molding.

Thickness-dependent Orientation Structure in Poly(ethylene oxide) Multi-layer Crystals

Poly（ethylene oxide） multi-layer crystals were obtained and the re-crystallization behavior was studied to give insight into how melt thickness and temperature affect the lamellar orientation. For a special re-crystallization temperature, there exists a critical transition thickness range for the occurrence of edge-on lamellar orientation. Below the critical thickness, only flat-on lamellae were observed. While above the critical thickness, both flat-on and edge-on lamellae were found and the proportion of the edge-on lamellae increases with thickness. At low re-crystallization temperatures （below 30 ℃）, the critical transition thickness gradually increases from about 15 nm to 35 nm when the re-crystallization temperature was increased from 20 ℃ to 30 ℃. However, when the re-crystallization temperature is above 30 ℃, the critical transition thickness becomes constant. Our results demonstrated that the lamellar orientation could be specially modified by changing the melt thickness and re-crystallization temperature.