Effect of thermal gradient field with phase change on crystal morphologies of HDPE during GAIM process

Abstract

To understand the effects of thermal gradient field with phase change on the crystal morphologies of high density polyethylene (HDPE) during gas assisted injection moulding (GAIM) process, the combination of the simulation of the temperature field via an enthalpy transformation method and the hierarchical structures and the crystalline morphology of HDPE were investigated in this work. The GAIM parts of HDPE 6098 can be grouped into four layers in the direction of thickness: skin layer, subskin layer, intermediate layer and core layer. Besides, the cooling logarithmic curves were adopted in this experiment, and it is found that they can clearly display the phase change plateaus even at the skin layer zone.

Role of gas delay time on the hierarchical crystalline structure and mechanical property of HDPE molded by gas-assisted injection molding

“…To distinguish the effect of different gas delay times on the temperature gradient developed across the thickness, the acquisition of temperature distribution immediate after the short shot (SS) injection process is imperative. From our previous research [13,14,20,34,35], a great deal of work has been carried out to simulate the temperature field during the GAIM process as well as conventional injection process. In order to validate the simulated results, experiments have been conducted to assess the calculated cooling curves and found the experimental results and the theoretical values fit well.…”

“…In order to validate the simulated results, experiments have been conducted to assess the calculated cooling curves and found the experimental results and the theoretical values fit well. The temperature fields after the SS process at different gas delay times were simulated via an enthalpy transformation method described before [13,14,20,34,35], as shown in Fig. 4.…”

“…On the other hand, a great deal of work has been conducted on the hierarchical structures [such as isotactic polypropylene (iPP) and polycarbonate/high-density polyethylene (PC/ HDPE), linear low-density polyethylene (LLDPE), PP, glass fiber reinforced isotactic polypropylene (GF/iPP), PC/PE, etc.] formed during GAIM process [15][16][17][18][19][20][21], as well as optimization of processing parameters based on measurements of the part mechanical performance [22][23][24][25]. When compared with CIM, the mechanical strengths of GAIM parts can be greatly improved; nevertheless, as far as we know, there still lack quantitative experimental data for conclusion that can be achieved till now.…”

“…More recently, we have intensively studied on the GAIM morphological characteristics as well as the hierarchy structures formed during the GAIM process such as HDPE, LLDPE, PP, GF/iPP, PC/ PE, etc. [15][16][17][18][19][20][21]. In a previous article, we presented the spatial variation of hierarchy structure, orientation behavior, and mechanical properties of HDPE samples obtained via GAIM under different gas pressures [32].…”

Microscopic analysis of the morphology of seams in friction stir welded polypropylene

“…In the case of all welding processes the temperature necessary for welding is at or above the melting range of the base material. This triggers melting and crystallization and vari-ous deformation processes in the molten and heat affected layers, respectively, similar to other polymer processing technologies [7,8]. Various friction welding methods were adapted for polymeric materials [6], and we have also dealt with the application possibilities of FSW in polymers [9].…”