A novel strategy for the preparation of long chain branching polypropylene and the investigation on foamability and rheology

Effect of phase compatibility on the foaming behavior of LDPE/HDPE and LDPE/PP blends with subcritical CO2 as the blowing agent

“…For L/H-0/10, the low melt strength, pure HDPE could not resist gas expansion during cell growth, thus resulting in large, collapsed cells. With a 20% LDPE content, the high melt strength of the LDPE phase with branched chains is clearly beneficial to the foaming process, which has been confirmed by a number of researchers [7,8,43]. The expansion ratio, cell density and cell size all showed a clear improvement.…”

“…During polymer extrusion in the absence of foaming, the die-swell is closely related to the viscoelastic properties of the polymer, especially the storage modulus [41]. During extrusion foaming, cell nucleation should not be ignored [8,42]. The relationship between the initial angle and cell nucleation could be interpreted as follows: the nucleated cell could be considered as the initial formation of the final bubble, and the higher initial angle is an indication that a larger number of newly formed bubbles is obtained following the significant pressure drop experienced as the material is pushed across the die.…”

“…Other linear polyolefin resins such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and isotactic PP have superior mechanical properties but are difficult to foam due to their low melt strength which cannot sustain cell growth during the foaming process. Many efforts have been made to produce foams from these so-called linear resins [7,8], in which a "two-stage-process" including cross-linking and radiation were used. In such approaches, some gel formation might occur, which is undesirable for the finished product [9,10].…”

Polymer nano-foams for insulating applications prepared from CO2 foaming

“…As, the cell growth process imposes high extensional action on the cell wall [103], the elongational viscosity has to be fitted to provide strain hardening in order to control the foam growth in micro-or nano-cellular foaming processes. Generally speaking, the use of branched polymers or long chain branches (LCB) is one of the research areas looking to stabilize cell growth and limit coalescence [104][105][106]. However, Otsuki and Kanai [107] showed, using a numerical simulation, that the strain-hardening characteristics of polymer does not strongly affect the cell growth rate, even for foaming processes at high temperature.…”

CO2 nano-foaming of nanostructured PMMA

“…As the cell growth process imposes high extensional action on the cell wall [53], the elongational viscosity has to be fitted to provide strain hardening in order to control the cell growth and limit the coalescence phenomenon. Generally speaking, the use of branched polymers or long chain branches is one of the research areas looking to stabilise cell growth [54][55][56]. However, even in these specific cases, some studies [57,58] have shown that the strain-hardening characteristics do not strongly affect the cell growth rate and that the linear viscoelastic characteristic appeared to be more influential in the cell growth mechanism.…”