Nucleating agents for high-density polyethylene-A review

Abstract

A review of nucleating agent (NA) types and their effect on crystallization in high-density polyethylene (HDPE) is presented. The focus is on methods to improve the physical properties of HDPE due to its widespread use in commercial applications and high volume use in typical industrial processes including extrusion, injection molding, and blow molding. The crystallization process in HDPE significantly affects its final optical, mechanical, and thermal properties. The addition of NAs affects the physical properties of HDPE by controlling the crystallization from the melt state. Specific NAs improve properties such as clarity, cycle time, and modulus. NAs are more widely developed for polypropylene (PP) than HDPE as its slower crystallization rate allows greater control in achieving property improvements. While certain NAs are effective in improving property characteristics in HDPE, greater control over the crystallization process would achieve further improvements in specific properties. Research has progressed in identifying effective NAs for HDPE, though the magnitude of the effects remains lower than those generally observed in PP. Inorganic and organic NAs are reviewed with an emphasis on the mechanisms by which they function. Fundamentals of polymer crystallization and modeling kinetics during both isothermal and nonisothermal studies provide the necessary framework for characterizing the effects of a NA in HDPE. Finally, the interactions between HDPE, NA, and industrial processing conditions as related to practical applications are discussed. POLYM. ENG. SCI., 56:541-554, 2016.

Protection of high‐density polyethylene–silicon composites from ultraviolet–visible photodegradation

“…120 °C). Similarly, the addition of Si microparticles accelerated the crystallization process by slightly shifting T c toward higher temperatures [Figure (d)] because of a nucleation effect of the Si microparticles, as also reported for composites made of HDPE and silica . The melting enthalpy did not significantly change after the addition of Si microparticles and remained in ranges between 175 and 190 J/g.…”

Influence of surface topography, crystallinity, and thermal conductivity on reflectance and color of metallic‐effect high‐density polyethylene parts filled with aluminum pigments

“…One is that the movement of the HDPE molecular chain is limited because the addition of fillers could entangle the chains and prevent the growth of the crystals. The other is that the addition of fillers promotes heterogeneous nucleation and improves the crystallization . As shown in Table , the addition of Al particles ensures that the crystallinity of the composites is better than that of pristine HDPE.…”

Isothermal crystallization kinetics and spherulite morphologies of poly(lactic acid)/ethylene acrylate copolymer blends

“…After most of the crystallization had taken place, a slow increase of crystallinity with time was observed, which can be attributed to the presence of secondary crystallization . Secondary crystallization occurs when crystallization slows due to the spherulites impinging on each other …”

“…The typical Maltese cross pattern for spherulites was visible in the micrographs of PLA and PLA/EAC blends. These spherulites grew in an outward direction until they encountered on adjacent spherulites, creating a space‐filling polycrystalline matrix . When PLA was crystallized at 95 °C for 17 min, some spherulites were formed and the size of these spherulites was relatively small because of low mobility of the PLA chains at this temperature.…”