The investigation of the influence of injection molding parameters (injection velocity, mold temperature and injection temperature, and additionally, as a result of these three parameters change, injection time, hold time, and cooling time) and blowing agent percentage on selected properties of HDPE molded parts such as weight, density, mechanical properties (tensile strength and elongation at maximum force), surface state (gloss and color), and structure was the aim of this work. The examination showed, that the mold temperature has the main influence on properties and surface state of molded parts from solid and foam HDPE. The weight, density, mechanical properties and gloss of molded parts increased with the increase in mold temperature. The mold temperature also influences significantly the number and size of pores in molded parts. The addition of blowing agent in a quantity of 2% is sufficient to obtain parts with favorable mechanical properties and good surface quality. POLYM. ENG. SCI., 53:780-791, 2013. FIG. 8. The change of the tensile strength of molded parts from HDPE: without blowing agent in function of the injection velocity v w and the mold temperature T f (T w ¼ 2308C) (a); the mold temperature T f and the injection temperature T w (v w ¼ 45 mm/s) (b), with 2% addition of blowing agent in function of the injection velocity v w and the mold temperature T f (T w ¼ 2308C) (c); the mold temperature T f and the injection temperature T w (v w ¼ 45 mm/s) (d), with 4% addition of blowing agent in function of the injection velocity v w and the mold temperature T f (T w ¼ 2308C) (e); the mold temperature T f and the injection temperature T w (v w ¼ 45 mm/s) (f).

The investigation of the influence of mould temperature and blowing agent percentage on structure, and selected properties (weight, mechanical properties, surface state - gloss and colour) of moulded parts from HDPE was the aim of this work. The structure of moulded parts in cross-section perpendicular and parallel to the direction of polymer flow, and quantitative assessment of porous structure using microscopic image analysis were carried out. It was shown that the content of blowing agent in polymer influences not only the amount of pores in the part core, but also the thickness of solid skin. Lower mould temperature favors the formation of a fine porous structure. The formation of the porous structure influenced slightly the weight and mechanical properties of moulded parts. With the increase in blowing agent content, the gloss of parts decreased and also caused the change in their colour. Parts with higher amount of blowing agent were brighter.

No abstract

Weld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. In the weld line area, the V‐shaped notch is formed and its shape and size depend on injection molding conditions and properties of processed polymer. Addition of the foaming agent to the polymer can be one of the way to improve conditions of melt streams welding due to the higher velocity of the colliding streams of unfilled polypropylene (PP) and PP filled with talc. The examinations of mechanical properties showed, however, lower tensile strength of porous parts compared to solid ones, but in the microscopic observation and measurements of the geometric structure of moldings, in the weld lines area, better surface conditions were achieved for samples made of the foamed polypropylene. The size of V‐notch, determined by the total height of the raw profile Pt, depends also on the length of polymer flow path from the gate to the weld line area. The values of Pt parameter increase with the length of the flow path, but this increase is smaller for foamed polypropylene. POLYM. ENG. SCI., 59:1710–1718 2019. © 2019 Society of Plastics Engineers

No abstract