Compatibilization of polypropylene–polystyrene blends: Part 2, crystallization behavior and mechanical properties

Abstract

Reactor produced blends of polypropylene (PP) and polystyrene (PS) are obtained by graft copolymerization of styrene onto polypropylene chains. This technique generates simultaneously a graft copolymer (PP-g-PS) and polystyrene homopolymer. The resulting blends, however, have a low impact resistance and have to be modified with the addition of rubbery toughening agents, such as an ethylene propylene copolymer (EPR) or a styrene-b-ethylene-alt-butylene-b-styrene (SEBS) triblock copolymer, in a downstream compounding operation. Part 1 of this work, which has been accepted for publication in the British Journal "Plastics, Rubber, and Composites", was concerned with the compatibilization efficiency and the effect of mixing intensity on the morphological and rheological properties. Part 2 of the study deals with interactions of the components of the blends. These interactions were assessed by monitoring the crystallization behavior and mechanical properties. Mixing experiments were conducted on a proprietary twin screw mixing element evaluator (TSMEE) and also on a commercial TSE-30Correspondence to: Akin Adewole. COMPATIBILIZATION OF POLYPROPYLENE -POLYSTYRENE BLENDSextruder. Differential scanning calorimetry (DSC) was used to determine the transition temperatures and the crystallinity of the blends specimens after annealing. The results show that both the free polystyrene and the graft copolymer, PP-g-PS, act as nucleators for the polypropylene phase, thus increasing both the degree of crystallinity and the crystallization temperature of the blends. While a good correlation was found between modulus and crystallinity, the factors affecting fracture behavior were less clearly discernible.

Relationship between branch length and the compatibilizing effect of polypropylene‐g‐polystyrene graft copolymer on polypropylene/polystyrene blends

“…Usually, such compatibilizers have blocks or graft segments that are chemically identical to those in the respective phases and work by improving the interfacial adhesion . Poly (styrene‐ b ‐butadiene‐ b ‐styrene) (SBS), poly(styrene‐ b ‐ethylene‐ co ‐butylene‐ b ‐styrene) (SEBS), poly(styrene‐ b ‐ethylene‐ co ‐propylene) (SEP), poly(styrene‐ b ‐isoprene‐ b ‐styrene) (SIS), and PP‐ g ‐PS copolymers can be used as compatibilizing agents for PP/PS blends. Among which, PP‐ g ‐PS graft copolymer, composed of a PP backbone and PS branches, is an ideal compatibilizer for PP/PS blends due to the good compatibilities of PP backbone and PS branches with PP bulk and PS bulk, respectively.…”

Crystallization kinetics and crystalline morphology of poly(ε‐caprolactone) in blends with grafted rubber particles

“…In the few cases for which the physical origin of the increased T c was discussed, the nucleation effect was attributed to the increased surface area of the dispersed phase after dynamic vulcanization and/or (reactive) compatibilization. 7,8,13 This paper discusses the influence of graft copolymer formation on dispersed rubber particles on the crystallization kinetics and crystalline morphology of the semi-crystalline matrix. A low-molar-mass poly(ethylene oxide) dimethacrylate (PEO9) resin is used as the rubber precursor, which is fully miscible with PCL above its melting temperature.…”

“…15,16 Similar changes in the crystallization behavior were observed after compatibilization of polymer blends by the addition of copolymers in the absence of crosslinking. Tang and Huang 12 reported an increase in T c for blends of PP and poly(ethylene oxide) (PEO) by compatibilization with a maleated PP-PEO copolymer, whereas Adewole et al 13 observed an increase in T c for PP in blends with poly (styrene) (PS) after the addition of a PP-PS graft copolymer. In the few cases for which the physical origin of the increased T c was discussed, the nucleation effect was attributed to the increased surface area of the dispersed phase after dynamic vulcanization and/or (reactive) compatibilization.…”

“…For polymer blends consisting of a semi-crystalline thermoplastic matrix and an amorphous dispersed phase, several examples show that crosslinking of the amorphous phase and/or interfacial reactions to improve the blend compatibility often lead to an increase in the onset temperature of crystallization upon cooling from the melt. [3][4][5][6][7][8][9][10][11][12][13] These changes in the crystallization process are known to affect the properties of the blend. The significant influence of the amorphous particles on the crystallization behavior is unexpected, because amorphous fillers are known to have only a very limited nucleating ability.…”

Nonisothermal crystallization kinetics of polypropylene/polypropylene‐g‐polystyrene/polystyrene blends

“…Their blends usually result in serious phase separation, low interfacial adhesion, and poor mechanical properties. As a compatibilizer, the PP‐ g ‐PS copolymer actually improves the interfacial adhesion and produces a finer dispersion mixing of PP/PP‐ g ‐PS/PS polymer blends and, thus, enhances the mechanical properties 4–11. Researchers have reported the development of morphologies and the rheological and isothermal crystallization behaviors of PP/PP‐ g ‐PS/PS polymer blends in detail.…”