Simultaneously enhancing strength and toughness for impact polypropylene copolymers by regulating the dispersed phase with high density polyethylene

Abstract

By introducing high density polyethylene (HDPE) into the dispersed phase of impact polypropylene copolymers (IPCs), the morphologies of IPC/HDPE blends were regularly tailored and consequently the tensile and impact properties were simultaneously improved. Morphological observations showed a series of multilayered core-shell dispersed particles when the content of HDPE was less than 40%, while the continuous network structure was observed beyond 40%. With an increase in the content of HDPE, the size of the core increased and the number of dispersed particles with incomplete encapsulated polyethylene (PE) cores rose. More valid 'bridges' made up of segmented ethylene-propylene copolymer (sEbP) appeared and connected the PE core and polypropylene (PP) matrix. Meanwhile, co-crystallization occurred in the core phase, between long ethylene chain segments of the joined HDPE and sEbP in multi-component IPCs. The increased HDPE in blends reduced defective co-crystals, and in turn led to a thicker average lamellar thickness and thinner amorphous thickness of PE. Partial inserted ethylenepropylene random sequences are constrained by narrowed PE amorphous layers. Hence, the connection between the PP matrix and the dispersed phase was strengthened by co-crystals, 'bridges' and restriction effects. The tensile strength of the blends was slightly enhanced with an increase in HDPE, while the greatly improved toughness was achieved at a HDPE content of 30 wt% and kept constant with more HDPE. Thus, the interactions rather than core-shell phase morphology are regarded as the predominate factor for the excellent properties.

Toughening mechanism in impact polypropylene copolymer containing a β-nucleating agent

“…In a non-ideal two-phase system, L is assumed to be the sum of average thicknesses of lamellae (L c ), amorphous layers (L a ) and transition zones (L tr ) (L ¼ L c + L a + 2L tr ). 39 Compared with the relaxed MAF, the transition zone is termed to the ordered RAF, distributed at the interface between the crystal and mobile amorphous layers. Those morphological parameters of the crystalline and amorphous fraction can be revealed by the correlation function k(z) (the eqn (2) in the Experimental section).…”

Influence of the HDPE molecular weight and content on the morphology and properties of the impact polypropylene copolymer/HDPE blends

“…The addition of PE is believed to increase the overall volume of the elastomer particles and thus lead to an increase in NIS. 3,7,12 It has been reported that there exists a maximum at a w PE of about 10 wt% in the NIS versus PE content curve of IPC/HDPE blends at room temperature. 7,11 Gahleitner et al 3 reported that NIS of a random-heterophasic copolymer/HDPE increases with increasing PE content at PE content of 0-15 wt% and changes little from 20 to 25 wt% at 23 C, but at À20 C, NIS goes down monotonically.…”

“…[2][3][4][5][6][7][8][9][10] Correspondingly, the relationship between the structure and properties of this type of multiphase materials has been intensively studied. Addition of HDPE was reported to inuence the impact strength, 2,3,6,7,9,11,12 minimize the magnitude of the modulus decrease, 2,3 and suppress the stress-whitening. 5,7 Mirabella studied IPC/HDPE blends with HDPE weight percent 0-40%.…”

Balanced toughening and strengthening of ethylene–propylene rubber toughened isotactic polypropylene using a poly(styrene-b-ethylene–propylene) diblock copolymer

“…That will no doubt cause the limitation of application for the products. However, considering impact polypropylene copolymer (IPC), a popular thermoplastic that exhibits a good rigidity-toughness balance and is widely used in automotive industry, 30,31 the aim of simultaneous achieving excellent toughness and high rigidity is not unrealistic. In recent years, different polymer materials with combined high toughness and stiffness were produced by several approaches.…”