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.

Solid‐state modification of isotactic polypropylene (iPP) via grafting of styrene. II. Morphology and melt processing

“…One population of PS domains retains the original size (50–100 nm) and the other increases in size up to 300 nm. Even within this limit, the morphology is much finer than that of physical iPP/PS blends and is at least comparable to what is oberved when iPP and PS are blended in the presence of a compatibilizer 1, 30–33…”

Solid‐state modification of isotactic polypropylene (iPP) via grafting of styrene. II. Morphology and melt processing

“…One population of PS domains retains the original size (50–100 nm) and the other increases in size up to 300 nm. Even within this limit, the morphology is much finer than that of physical iPP/PS blends and is at least comparable to what is oberved when iPP and PS are blended in the presence of a compatibilizer 1, 30–33…”

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.…”

Calorimetric Analysis of Uncompatibilized Polypropylene/Polystyrene Blend Using DSC

“…PP/PS blends are immiscible due to the non‐polar nature of the polymer and hence it is also incompatible . Several authors have discussed about the compatibility of PP/PS blend using different compatibilizer . In this paper our main aim is to study the thermal behaviour such as glass transition, melting, crystallization and specific heat of uncompatibilized PP/PS polymer blends using DSC.…”

Solid‐state modification of isotactic polypropylene (iPP) via grafting of styrene. II. Morphology and melt processing

“…One population of PS domains retains the original size (50–100 nm) and the other increases in size up to 300 nm. Even within this limit, the morphology is much finer than that of physical iPP/PS blends and is at least comparable to what is oberved when iPP and PS are blended in the presence of a compatibilizer 1, 30–33…”

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.…”

Calorimetric Analysis of Uncompatibilized Polypropylene/Polystyrene Blend Using DSC

“…PP/PS blends are immiscible due to the non‐polar nature of the polymer and hence it is also incompatible . Several authors have discussed about the compatibility of PP/PS blend using different compatibilizer . In this paper our main aim is to study the thermal behaviour such as glass transition, melting, crystallization and specific heat of uncompatibilized PP/PS polymer blends using DSC.…”

Solid‐state modification of isotactic polypropylene (iPP) via grafting of styrene. II. Morphology and melt processing

“…One population of PS domains retains the original size (50–100 nm) and the other increases in size up to 300 nm. Even within this limit, the morphology is much finer than that of physical iPP/PS blends and is at least comparable to what is oberved when iPP and PS are blended in the presence of a compatibilizer 1, 30–33…”

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.…”

Calorimetric Analysis of Uncompatibilized Polypropylene/Polystyrene Blend Using DSC

“…PP/PS blends are immiscible due to the non‐polar nature of the polymer and hence it is also incompatible . Several authors have discussed about the compatibility of PP/PS blend using different compatibilizer . In this paper our main aim is to study the thermal behaviour such as glass transition, melting, crystallization and specific heat of uncompatibilized PP/PS polymer blends using DSC.…”