As the world’s population grows, an enormous amount of waste is generated that is derived from polymeric materials, contributing to environmental and social impacts [1
]. Polypropylene (PP) is one of the most requested polymers in the world for developing manufactured goods such as food packaging, bags for grains and fertilizers, plastic chairs, industrial containers, toys, and plastic cups [2
]. High consumption of PP leads to an increased production of post-industrial waste and, consequently, the practice of mechanical recycling is encouraged due to PP’s beneficial properties [4
PP is a semicrystalline polymer known commercially for presenting an excellent balance of properties, including high chemical resistance, reasonable ductility, good stiffness, low density, and excellent processability [5
]. Therefore, developing polymeric mixtures with recycled PP is increasingly explored, because it allows the reduction of waste deposited in the environment and contributes to the production of materials with good properties [7
The heterophasic copolymer polypropylene (PP) is a complex material. It has both a homopolymer PP matrix and dispersed ethylene/propylene particles. Generally, copolymer PP is used in applications that require high impact strength, such as industrial containers [8
]. At present, Brazil is one of the largest PP producers worldwide, and it has the largest industrial park in Latin America for the production of industrial containers [9
]. This stems from the high demand for industrial containers. In this context, the production of post-consumption waste is high, and waste also arises from the need to dispose of damaged industrial containers derived from copolymer PP. Copolymer PP residues are a source of environmental pollution and raw material waste. They are also associated with beneficial properties and high added value, including the technological potential to be used as a polystyrene (PS) impact modifier.
As a transparent and fragile thermoplastic with good tensile properties, PS can easily be synthesized, processed, and recycled, and it is resistant to biological degradation [10
]. However, it has low impact strength and, therefore, it must be toughened for certain applications [11
]. PS toughening has already been explored in the literature with styrene-butadiene (SBR), styrene-butadiene-styrene (SBS), styrene-butylene/ethylene-styrene (SEBS), and ethylene propylene-diene (EPDM) rubbers [12
]. However, despite the fact that these rubbers achieve satisfactory PS impact strength, they severely reduce tensile properties and thermomechanical strength. To improve the properties of polystyrene without incurring severe losses in tensile properties, the research [17
] was directed towards polystyrene/polypropylene mixtures using compatibilization agents.
Samsudin et al. [20
] investigated the chemical resistance of polystyrene (PS)/polypropylene (PP) mixtures compatibilized with SEBS. The results showed that the chemical resistance of PS to acetone and tetrahydrofuran (THF) increased. The chemical resistance of PS/PP mixtures increased with the increase in the SEBS content and a relatively low PP content. However, it decreased when the SEBS content increased and a high PP content was used. Semicrystalline polypropylene has been shown to increase the chemical resistance of PS.
Halimatudahliana et al. [21
] evaluated the effect of several compatibilizers on the mechanical properties of polystyrene/polypropylene mixtures. The PS/PP blends in the compositions 20/80, 50/50, and 80/20 (% by weight) were prepared in a single screw extruder. In general, styrene-(ethylene/butylene)-styrene (SEBS) was the best compatibilizer for PS/PP mixtures. When the PS/PP mixture was made compatible with 7.5%, toughness was improved in all compositions. Additionally, the fragile behavior of polystyrene was converted to extreme ductility with PS/PP mixtures compatible with SEBS.
Latreche et al. [22
] developed polystyrene/polypropylene mixtures compatibilized with several compatibilizers. Generally, the compatibilizer tended to reduce the interfacial tension between the phases, generating greater morphological stability, in comparison with the non-compatibilized blend. The ductility and impact strength properties were enhanced when the PS/PP blend was compatibilized with SEBS. However, there was a reduction in microhardness and in the degree of crystallinity, indicating an increase in the flexibility of the PS/PP/SEBS blends.
Luna et al. [23
] investigated the toughening of polystyrene (PS) with hybrid mixtures of copolymer polypropylene (PP) and recycled polypropylene (PPr), using SEBS as a compatibilizing agent. The results showed that the mixtures presented a pseudoplastic fluid behavior, according to complex viscosity analysis. There was an increase in impact strength, elongation at break, thermal stability (TG), and heat deflection temperature (HDT) of the mixtures, compared to neat PS. For PS/PP/PPr/SEBS mixtures in the investigated composition range of PPr (7%, 14%, and 21% by weight), there were no significant differences in the properties of the mixtures. In this case, a greater amount of recycled material can be used without compromising properties.
The mixture of polystyrene (PS) and polypropylene (PP) is one of the most studied, mainly due to the low cost and technological relevance of these materials [24
]. Most PS/PP mixtures are developed using homopolymer PP and, at the same time, it is not recycled. Despite PP’s potential to improve the properties of polystyrene, there is practically no work in the literature that used recycled copolymer PP to toughen PS. Both the economic and environmental benefits are justification for research evaluating the potential of this recycled material.
This work aimed to study polystyrene/recycled copolymer polypropylene mixtures, using styrene-(ethylene/butylene)-styrene (SEBS) as a compatibilizing agent.
Copolymer polypropylene from industrial containers has the potential to be reused as a polystyrene impact modifier as long as it uses a suitable compatibilizer. In this study, the PS/PPr/SEBS mixture (70/20/10 %wt.) showed the greatest synergism of properties, with gains in impact strength, elongation at break, and thermomechanical strength. Additionally, no severe reduction occurred in elastic modulus or tensile strength. The results of the PS/PPr/SEBS mixtures are significant in the area of polymer recycling, with potential for applications in household utensils, CD packaging, toys, and organizing boxes. The results also indicate a good perspective for further studies with this material, with the aim of increasing the content of recycled material in the formulations and, consequently, to minimize harmful environmental effects and add value to a discarded material.