He Guangjian

Influence of pressure oscillation on injection molding process

A self-made vibration-assisted injection molding machine (VAIM) was developed to generate oscillation injection pressure during filling and packing The cavity pressure changes sinusoidal with time during filling and packing in VAIM. The filling time can be shortened with the introduction of oscillation injection pressure. The melt peak of the parts become wider and the melt point move to high temperature with the increase in piston rod vibration amplitude/frequency.

Ultrasound-assisted melt mixing for the preparation of UHMWPE/OMMT nanocomposites

Ultrahigh molecular weight polyethylene (UHMWPE)/organic montmorillonite (OMMT) nanocomposites were prepared via a self-made vane mixer which could supply a synergy of ultrasound and extensional deformation. Structure and working principle of this novel mixer were illustrated in detail. Effects of the OMMT content, mixing time, and ultrasound treat time on composites’ morphology, rheological properties, and thermal properties were reported in terms of transmission electron microscopy (TEM), wide-angle X-ray scattering, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). X-ray diffraction (XRD) and TEM showed that the OMMT lay spacing increased from 2.82 nm to 3.29 nm and OMMT dispersed evenly in the matrix using this novel melt mixing equipment. It certified that the melt mixing procedure synergized by ultrasound and extensional deformation was very effective in the exfoliation of silicate layers and also the filler distribution and dispersion. DSC measurements revealed that the crystallization temperature (T c) had no visible change with increasing the OMMT content and the melting temperature (T m) and melting enthalpy crystallinity (X c) increased with the proper OMMT content. The higher T m and X c showed with the proper ultrasound treatment time, however, the T c had no visible change. TGA showed that the onset temperature at which 20% weight loss of the material increased markedly in the case of UHMWPE/OMMT-1 wt% nanocomposite. The onset temperature slightly decreased with the use of ultrasound. Rheological analyses showed that all the samples exhibited non-Newtonian and shear thinning characteristics. Both the storage modulus and complex viscosity increased with continuous addition of the OMMT layers. It also indicated that the introduction of ultrasound tended to decrease the storage modulus and complex viscosity. Universal tensile test indicated that superior tensile strength occurred in samples containing OMMT layers.