Hierarchical crystalline structure of HDPE molded by gas-assisted injection molding

Advanced Injection Molding Methods: Review

Injection molding is a method commonly used to manufacture plastic products. This technology makes it possible to obtain products of specially designed shape and size. In addition, the developed mold allows for repeated and repeatable production of selected plastic parts. Over the years, this technology grew in importance, and nowadays, products produced by injection molding are used in almost every field of industry. This paper is a review and provides information on recent research reports in the field of modern injection molding techniques. Selected plastics most commonly processed by this technique are discussed. Next, the chosen types of this technique are presented, along with a discussion of the parameters that affect performance and process flow. Depending on the proposed method, the influence of various factors on the quality and yield of the obtained products was analyzed. Nowadays, the link between these two properties is extremely important. The work presented in the article refers to research aimed at modifying injection molding methods enabling high product quality with high productivity at the same time. An important role is also played by lowering production costs and reducing the negative impact on the environment. The review discusses modern injection molding technologies, the development of which is constantly progressing. Finally, the impact of the technology on the ecological environment is discussed and the perspectives of the process were presented.

Influence of Diameter on the Templated Crystallization of Polyethylene/Carbon Material Fiber Composites under Intense Shear Flow

In this study, carbon fibers (CFs) and carbon nanofibers (CNFs) were introduced into polyethylene (PE) and intensive shear flow was imposed on the melt during the melt second flow caused by gas penetrating the melt during the gas-assisted injection molding (GAIM). The effect of fiber diameter on crystalline morphologies of obtained composites was deeply studied. The results revealed the fact that no matter whether CFs or CNFs were introduced into the PE matrix or not, the orientation degree of PE lamellae would increase during the melt second flow. Hybrid shish-kebab structures were difficult to be formed in GAIM CF/PE composites and only a few oriented PE lamellae overgrew on the local surface of CFs. However for GAIM CNF/PE composites, the formation of hybrid shish-kebab structures was clearly observed in the entire thickness. The structural diversity was mainly ascribed to the difference of CF diameter, showing obvious size-dependent effect.

Influence of HMW tail chains on the structural evolution of HDPE induced by second melt penetration

It is widely accepted that the role of the high molecular weight (HMW) component is cooperative in shear-induced crystallization, owing to entanglements among long chains. However, this paper demonstrates that the HMW component has a novel effect on structural evolution during the process of multi-melt multi-injection molding (M³IM), organized as follows. First, the appropriate HDPE system with an incremental concentration of HMW tails was established. Second, the crystalline morphologies and orientation behaviors of the M³IM samples were characterized using a combination of scanning electron microscopy (SEM) and two-dimensional small angle X-ray scattering (2D-SAXS), and these suggested that the amount of shish-kebabs was not monotonically promoted with an increasing content of HMW tails but tended to reduce at a certain value. Third, in order to explain this phenomenon, the special temperature and shear profiles of M³IM were depicted subsequently, and finally the mechanism of hierarchical structure formation with the influence of various amounts of HMW tail chains was discussed, based on the classical rheological viewpoint.

Formation of various crystalline structures in a polypropylene/polycarbonate in situ microfibrillar blend during the melt second flow

A special shell–core structure is formed in PP/PC/β-NA composites, which has huge potential for the improvement of mechanical performance.

An unusual transition from point-like to fibrillar crystals in injection-molded polyethylene articles induced by lightly cross-linking and melt penetration

Recently, an unusual transition from point-like to fibrillar crystals has been realized by lightly cross-linking structure and melt penetration.

Hierarchical crystalline morphologies induced by a distinctly different melt penetrating process

It is the first time that hierarchically crystalline morphologies induced by melt penetration of the melt with different interactions.

Unusual hierarchical distribution of β-crystals and improved mechanical properties of injection-molded bars of isotactic polypropylene

Shish-kebab and β-cylindrite morphology were observed simultaneously in the GAIM iPP part, which showed greatly improved mechanical properties.