Improved Cell Morphology and Surface Roughness in High-Temperature Foam Injection Molding Using a Long-Chain Branched Polypropylene

Abstract

Long-chain branched polypropylene (LCB PP) has been used extensively to improve cell morphologies in foaming applications. However, most research focuses on low melt flow rate (MFR) resins, whereas foam production methods such as mold-opening foam injection molding (MO-FIM) require high-MFR resins to improve processability. A systematic study was conducted comparing a conventional linear PP, a broad molecular weight distribution (BMWD) linear PP, and a newly developed BMWD LCB PP for use in MO-FIM. The effects of foaming temperature and molecular architecture on cell morphology, surface roughness, and mechanical properties were studied by utilizing two chemical blowing agents (CBAs) with different activation temperatures and varying packing times. At the highest foaming temperatures, BMWD LCB PP foams exhibited 887% higher cell density, 46% smaller cell sizes, and more uniform cell structures than BWMD linear PP. Linear PP was found to have a surface roughness 23% higher on average than other resins. The BMWD LCB PP was found to have increased flexural modulus (44%) at the cost of decreased toughness (−88%) compared to linear PP. The branched architecture and high molecular weight of the BMWD LCB PP contributed to improved foam morphologies and surface quality in high-temperature MO-FIM conditions.

Lightweight Polypropylene/Polylactic Acid Composite Foams with Controllable Hollow Radially Gradient Porous Structures for Oil/Water Separation

“…Hence, how to improve the melt strength and foaming behavior of the PP is always a research hotspot. In general, the methods of in situ fibrillated, adding nanoclay, and long-chain branches were used to improve the melt strength of the PP matrix. − Moreover, our previous works found that the novel hollow hierarchical structure, which had excellent filtration characteristics, can be prepared through the adjustment of miscible systems like PP copolymer and high melt strength PP (HMSPP), but whether the polymer composites systems can produce the hollow radially gradient porous structures and its functional mechanism still needs to be further studied.…”

Effect of Gas Counter Pressure on the Surface Roughness, Morphology, and Tensile Strength between Microcellular and Conventional Injection-Molded PP Parts

“…Microcellular injection technology [ 24 , 25 , 26 ] is a special process to overcome some problems that the conventional injection molding cannot. Most of the microcellular foam plus GCP technology [ 27 , 28 ] emphasizes improving surface roughness problems. Very few papers discuss the effect of GCP on the flow length, tensile property, and gas penetration problem.…”

“…In this study, the surface quality of microcellular foam is controlled using a pressure–temperature path control method. Prior studies only discussed the effects of temperature [ 27 ] or pressure [ 16 ]. This study investigates combined effects by temperature and pressure, aiming at optimizing parts’ surface quality in the foaming process.…”

Fabrication of Microcellular Injection‐Molded Polypropylene with Super High Expansion Ratio by Precision Mold Opening Technology

“…[28] The surface defects of the microcellular injection molded foam make it difficult to use as appearance parts. [29,30] Thus, researchers are trying to withdraw the mold core and open the mold cavity for a distance to prepare the microcellular injection molded PP Glass fiber 20% 64.29% Mechanical property, foam structure [40] BMWD LCB PP UC CBA 2% -Surface roughness, mechanical property [42] PP PTFE 5% 95% Thermal conductivity, foam structure [43] LCB PP POE 20% -Mechanical property [44] co-PP --58% Foam structure, foaming behavior [29] foam with a high expansion ratio, very low density, as well as maintain the characteristics of microcellular injection molding products. [24,31] Wu et al [32] explored mold opening foam with a chemical foaming agent, and investigated the mechanical properties and weight reduction.…”