The growing need of multifunctional materials with tailor made properties led in the last decades to the development of novel commercial polymer blends, possessing superior physical properties with respect to traditional matrices and showing economical advantages with respect to the synthesis of new plastics. Due to the progressive increase of the environmental concerns on the management of plastic wastes, the difficulties in the sorting technologies and the limited chemical compatibility between the greatest part of polymer pairs, the technical potential of polymer blends often remains unexploited when the recycling stage is considered. In some cases, also the addition of compatibilizers to recycled blends does not represent a satisfactory solution to retain and/or tailor their properties.

The aim of this review is that to perform a critical analysis of the potentialities of polymer blends recycling. After an introductive section on the problems and the definitions of plastics recycling, some basic concepts about the physical behaviour of polymer blends are reported. The third section of the review is focused on the analysis of the mechanical recycling of polymer blends, and a general distinction between recycling techniques applied to compatible and un-compatible polymer blends is performed. In this chapter, also the analysis of the recycling potential of commingled plastics deriving from unsorted wastes and of the effect of the thermal reprocessing on the morphological and thermo-mechanical behaviour of polymer blends is reported. Considering the increasing importance of bioplastics in the modern society, the fourth chapter of this review is focused on the mechanical and chemical recycling of blends containing bioplastics, with particular attention to polylactic acid (PLA) and thermoplastic starch (TPS) based blends. The key aspects of the recycling technologies applied to polymer blends and the future perspectives are summarized in the last section of the review.

PC/PBT blends have excellent comprehensive properties and are widely used in the market. It's inevitable that transesterification reaction will take place in the melting process for this kind of blends, and this reaction has decisive effects on the blend properties, in this paper, the effects of resin ratio of PC to PBT, resin viscosity and processing technology on the transesterification reaction degree were studied. Considering that the reaction occurred at the phase interface of PC and PBT, with the combination of the phase morphology and crystallization behavior of PBT phase under different resin ratios, the correlation between phase morphology and transesterification degree was established. From the perspective of PBT phase, the lower its ratio is, the smaller its phase size is, the worse its crystallinity is, and the greater the transesterification degree, besides, the lower PBT resin viscosity, the higher the transesterification degree. Moreover, through the research on processing technology, the higher the extruder speed, the higher the transesterification degree. Those studies will provide direct guidance for further research on the influence factors of the transesterification degree and the actual processing of the corresponding products.

Itaconic anhydride (IAn) was firstly used for the modification of poly(propylene carbonate) (PPC) by solution blending following with the direct heating treatment, producing end-capped and cross-linkable PPC (PECPPC) with high performance. The reaction of PPC with IAn was detailed investigated and the structure of PECPPC was identified by FTIR and ¹H NMR. A facile strategy including end-capping and cross-linking can be developed to improve the performance of PPC. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements revealed that the glass transition temperature (T_g) and thermal decomposition temperature (T_d) of PECPPCs are all much higher than those of PPC and increased with the increasing content of IAn. Tensile tests also showed the huge enhancement on the mechanical properties of PPC with the end-capping and cross-linking techniques, and the highest tensile strength of PECPPC4 is 37.5 MPa. Furthermore, ECPPC4 exhibits high hydrolysis rate in phosphate buffer solution (PBS) than that of PPC. It is demonstrated that the strategy with the combination of end-capping and cross-linking is efficient for the perfect modification of PPC with IAn.

In this study, we prepare series of low-density polyethylene (LDPE)/recycled polyethylene terephthalate (RPET) blends using melt extrusion. The effects of RPET content on the crystallization behavior and thermal conductive properties of the resultant blends were investigated using DSC, XRD, DMTA, TGA, etc. RPET was found to exert nucleating effect on the melt crystallization of LDPE without changing LDPE's crystal form. A four-parameter model (FPM) was adopted coupled with an in-situ temperature measurement to further disclose the solidification kinetics of LDPE in the presence of RPET. Among three thermal conduction models, the Agari model presented a reasonable prediction of thermal conductivity as a function of LDPE loading. A coefficient of cooling rate (CCR) is proposed and can be applicable as an indicator for thermal conductivity (λ) of the polymer blends.

Composites based on poly (trimethylene terephthalate) (PTT)/acrylonitrile butadiene styrene (ABS) blend with maleic anhydride grafted PTT (PTT-g-MA) as a compatibilizer and carbon nanotubes (CNTs) as reinforcers were prepared via melt-mixing, and the mechanical, electrical, and barrier properties of the as-fabricated composites were evaluated. Scanning electron microscopy (SEM) characterization of the cross-section of the composites after tensile test showed improved phase stability in the presence of the compatibilizer PTT-g-MA. The toughness of the composites was also improved with the addition of the compatibilizer and CNTs. Electrical conductivity tests were carried out and the results showed that CNT-reinforced composite exhibited significantly increased conductivity. Since barrier properties are very sensitive to structural changes, the oxygen transmission rate (OTR) of the composites was measured and the results showed that the composites possess a much high oxygen barrier compared to that of the neat PTT or ABS.

For high-value use of recycled polyethylene terephthalate (r-PET) resource and simultaneous development of high performance isotactic polypropylene (PP) materials, the blends of r-PET with PP and its compatibilized versions were prepared. PP-g-MA, POE-g-MA and EVA-g-MA with same functional group, as well as their mixtures, were used as compatibilizer. The crystallization behavior, mechanical properties and microphotographs of r-PET/compatibilizer, r-PET/PP bleds and its compatibilized versions were characterized. The results indicated that addition of compatibilizer decreased the tensile and flexural strength of r-PET and slightly improve its impact strength. The introduction of r-PET to PP matrix increased the tensile and flexural strength of PP. The tensile and flexural strength of compatibilized r-PET/PP are dependent on the kinds of compatibilizers. Addition of PP-g-MA improved the tensile and flexural strength of r-PET/PP blends and introduction of POE-g-MA or EVA-g-MA increased the impact strength of r-PET/PP blends. Effect of compatibilizer and its mixtures and r-PET content on the mechanical properties of compatibilized r-PET/PP blends is discussed. The r-PET/PP blends with high strength and toughness can be obtained by compatibilization of the mixtures of PP-g-MA and POE-g-MA (or EVA-g-MA). This investigation provides an effective method to use the r-PET to prepare high performance PP blends with low cost and high-value.