Preparation of long‐chain branching polypropylene and investigation on its foamability

Abstract

In this work, zinc N,N‐dimethyldithiocarbamate (ZDMC) was used to mediate the melt modification of polypropylene (PP) with 1,6‐hexanediol diacrylate (HDDA) in an internal mixer in the presence of dicumyl peroxide (DCP). Fourier transformed infrared spectroscopy analysis revealed that HDDA was directly grafted onto PP backbone. The dependence of torque on processing time indicated that the presence of ZDMC restrained the degradation of PP, and the end‐torque value increased with the addition of ZDMC. Dynamic rheological measurement indicated that the modified PP possessed higher G′ and lower tan δ at low frequency, displaying an increase in η* and disappearance of Newtonian plateau in η*–ω plot, as well as larger radius of semicircle in Cole–Cole plot. All the rheological characterizations, together with the decreased gel content with the increase of ZDMC, confirmed the formation of long‐chain branching. Subsequently, the foamability of the modified samples was investigated by one‐step compression–molding process. The cellular structure and morphology of the obtained foams were observed by scanning electron microscopy, and the results showed that the addition of ZDMC decreased the cell size, increased the cell density, and brought about well‐defined closed cell structure. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Improving melt strength of polypropylene by minimal branching and blending

“…Consequently, most PPbs synthesized in this way display highly heterogeneous molecular structures with hyper‐branched fractions. Better results can be obtained by using co‐agents (generally disulfides) that limit the scission reactions favoring branching …”

“…The most frequently used post-reaction mechanisms are irradiation 6,7 and reactive processing. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Particularly, reactive processing has aroused great interest because of its flexibility and relatively low cost as it can be implemented on an extruder, which is the most common equipment in industrial plastic processing.…”

“…The route frequently followed to obtain long-chain branched PP (PPb) from PP involves one reactive step where a polyfunctional monomer is used together with a peroxide. 1,9,11,14,16,18,[20][21][22]26 In that sense, the most frequently used peroxides are dicumyl peroxide (DCP) 14,18,21,25 and 2,5-dimethyl-2,5(tert-butyl peroxy) hexane (DBPH), 9,11,20,26 while the most chosen monomers are acrylates. 9,11,16,18,[20][21][22]26 The main drawback of the one-step procedure is that the branch density is not easily controlled.…”

“…Better results can be obtained by using co-agents (generally disulfides) that limit the scission reactions favoring branching. 9,18,20,22 The other methodology used to synthesize PPb by reactive mixing involves two processing steps. The first step comprises the functionalization of PP with a grafting agent (PPg), which is followed by the crosslinking of the PPg with a chain-linking agent in a second step.…”

Synergistic lignin construction of a long-chain branched polypropylene and its properties

“…where f is the expansion ratio, r is the density before foaming, r f is the density aer foaming, and V f is the bubble ratio. 33 The morphology of the foaming sample was observed with a scanning electron microscope (SEM), JSM-IT300LV (JEOL corporation of Japan). The sample was dipped into liquid nitrogen for 5 min to be quenched, and then glued to the aluminum sheet with a conductive adhesive.…”