Correlation between the fracture toughness and β‐crystal fraction in a β‐nucleated propylene‐based propylene–ethylene random copolymer

Abstract

Propylene‐based propylene–ethylene random copolymer (PPR) has been widely used in the production of hot‐water pipes. To further improve its toughness and thermal resistance, β‐nucleating agents (β‐NAs) are frequently incorporated. In this study, PPR containing 5.6 mol % ethylene units was modified by two kinds of β‐NAs, that is, calcium pimelate and N,N′‐dicyclohexylterephthalamide. The notched Izod impact strength of PPR increased with the addition of the β‐NAs. Drastically different toughening effects were found between the two β‐NAs. The structure of PPR with and without a β‐NA was investigated by calorimetry, X‐ray diffraction, and thermomechanical analysis. The results indicated that the relative fraction of β crystals (kβ) in the injection‐molded specimens was determined by the type and content of β‐NA. The relationship between kβ and the impact toughness was summarized. A critical value for kβ (0.68) was identified for the brittle–ductile transition of PPR. PPR with β‐NA having a kβ greater than 0.68 displayed a higher impact strength than the other mixtures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42930.

Synergistic enhancement of crystallization and mechanical performance of polypropylene random copolymer by strong shear and β‐nucleating agent

“…This difference indicates that more energy was absorbed in the presence of β crystals; the reason is that β crystals have a looser lamellar packing compared with α crystals. The specific structure of β crystal allows the initiation and propagation of plastic deformation easier, which benefits the improvement of toughness . The SEM results are consistent with the aforementioned results of impact strength (Fig.…”

“…The mechanical properties of semicrystalline polymers are directly correlated with crystalline orientation, crystalline morphology and crystalline structure; therefore, the above microstructures of these samples were characterized by using 2D‐WAXD, 2D‐SAXS and DSC techniques.…”

“…Polypropylene random copolymer (PPR) is prepared by copolymerization of propylene and α‐olefin. Compared with isotactic polypropylene homopolymer (iPP), the crystallizability of PPR is reduced due to the lower isotacticity with the incorporation of comonomers in the molecular chain; correspondingly its toughness is improved . Similar to iPP, PPR can also crystallize in three crystal forms, namely the monoclinic α‐form, the trigonal β‐form and the orthorhombic γ‐form, depending on the crystallization conditions such as crystallization temperature, shear strength, nucleating agent and cooling rate.…”

“…β crystal exhibits higher toughness than α and γ crystals due to the looser packing of lamella. Therefore, a good way to further improve the toughness of PPR is by inducing the formation of β crystal . PPR and PPR nucleated by β‐NA have key applications in water pipe production.…”

Exploring the polymorphic behavior of a β‐nucleated propylene‐ethylene random copolymer under shear flow

“…The content of ethylene units is ~5.6 mol%, as measured by 13 C‐NMR. Calcium pimelate (Ca‐Pim), an efficient β ‐NA for P‐E random copolymer, was synthesized by neutralization reaction between Ca(OH) 2 and pimelate acid.…”