Enhanced strain hardening in elongational viscosity for HDPE/crosslinked HDPE blend. II. Processability of thermoforming

Abstract

Rheological properties and processability of thermoforming were studied for high-density polyethylene (HDPE) and a blend of HDPE with crosslinked HDPE (xH-DPE). Blending the xHDPE, which enhances melt strength and strain hardening in elongational viscosity of HDPE, helps the sheet avoid sagging in thermoforming. Moreover, the product of the blend obtained by vacuum forming has uniform wall thickness. Melt strength and strain hardening of the blend were, however, depressed by a processing history in a single-screw extruder, whereas reprocessing by a two-roll mill enhanced the melt strength again. It is considered that the processing history by a single-screw extruder, in which shear-dominant flow takes place, depresses the trapped entanglements between network chain of xH-DPE and linear HDPE molecules, and results in low level of melt strength.

Impact of processing history on rheological properties for branched polypropylene

“…Since the viscous properties are hardly changed by mixing the gel, the technique would be widely available for various linear polymers [3,4]. Kolodka et al have studied the rheological properties of the copolymers composed of ethylene-propylene macromonomer and propylene, and found that activation energy of the obtained graft copolymer, 51 kJ/mol, is higher than that of a conventional linear PP, about 40 kJ/mol [5].…”

Development of a Thermoplastic Olefin Blend Embo-Pattern Sheet Cross-linked by Electron Beam Irradiation for Luxurious Automotive Interior Parts

“…However, it has a shorter period and a larger irradiation depth than other irradiations [13] . And also compare to grafting method, it is clean, highly efficient, and easy in operation [13,14] . The end result is outstanding mechanical properties at both low and high temperatures, very high chemical resistance, intensity, and heat resistance, all of which make electron beam cross-linking technology highly effective in cross-linking solid sheets applied to automotive skin materials [11][12][13][14][15][16][17] .…”

“…In particular, cross-linking using electron beam irradiation can readily improve several polymer properties (such as thermal stability) [11][12][13][14][15][16][17] and cross-link solid polymers like gamma ray irradiation and ultraviolet light irradiation [13] . However, it has a shorter period and a larger irradiation depth than other irradiations [13] .…”

“…Polymer cross-linking is a technology conducive to improving material properties (such as hardness, Young's modulus, heat resistance, and solvent resistance) [11][12][13][14][15][16][17], and processability [13,14] . In particular, cross-linking using electron beam irradiation can readily improve several polymer properties (such as thermal stability) [11][12][13][14][15][16][17] and cross-link solid polymers like gamma ray irradiation and ultraviolet light irradiation [13] .…”

Mechanical properties of radiation cross linked polyamide 12 after vacuum thermoforming

“…To prevent film destruction during prestretching and forming as well as flow of polymeric melt in the vacuum holes a certain elongational viscosity of the film is needed, preferably over a broad temperature range, to have a large processing window. Different authors determined uniaxial elongational viscosities in the range of 10 5 -10 7 Pas for polyethylen (PE) and polypropylene (PP) at forming temperatures as sufficient [6][7][8]. According to Hylton the ideal magnitude is 10 7 Pas [4].…”