Effect of different peroxide initiators on the reaction extrusion of polypropylene-graft-cardanol and its compatibilization on PP/PC

Improving the properties of polylactic acid/polypropylene carbonate blends through cardanol-induced compatibility enhancement

Cardanol (CD) is used as a reactive compatibilizer, and blended with polylactic acid (PLA) and polypropylene carbonate (PPC) resin (70/30(w/w)) to obtain a series of PLA/PPC/CD blends. The systematic study was conducted on the thermal properties, optical properties, rheological properties, mechanical properties, and microscopic morphology of the blend, by varying amounts of CD added to the blends. A detailed explanation and comprehensive analysis of the reaction mechanism between CD and PLA/PPC have been made. The study found that CD acts as a "bridge" between the PLA and PPC, forming the structure of a block copolymer (PLA-b-CD-b-PPC), and the copolymer can greatly improve the compatibility of PLA and PPC. When the amount of CD reaches 8 wt%, only one Tg is observed in the blend, simultaneously, PLA/PPC has already transitioned from a partially compatible system to a completely compatible system. At the same time, the addition of CD does not have any negative impact on the thermal stability of the PLA/PPC blend under processing temperature conditions, and the thermal stability of the PLA/PPC/CD blends can even be improved under extreme conditions. In addition, the addition of CD allows the PLA/PPC/CD blends to maintain a high light transmittance while reducing the opacity of the blend (the light transmittance remains above 92 %, and the opacity is reduced from 37 % to about 24 %), demonstrating excellent optical properties. Moreover, the elongation at break and impact strength of the PLA/PPC/CD blend both show a trend of first increasing and then decreasing with the increase of CD amount. When the CD amount varies within the range of 6- 8 wt%, the blends undergoes a brittle-ductile transition, and its toughness is greatly improved while the rigidity can also meet practical needs. When the amount of CD in the system increases to 12 wt%, the toughness of the blend reaches its peak, and its elongation at break and impact strength reach 513.24 % and 9211.5 J/m2 respectively (increased to 2442.84 % and 270.73 % of the PLA/PPC blend). Concurrently, the fracture surface of the blend exhibits large-scale plastic flow in the direction of the applied force, with marked shear yield phenomena, showing obvious characteristics of tough fracture.

Influence of Different Types of Peroxides on the Long-Chain Branching of PP via Reactive Extrusion

Long-chain branching (LCB) is known as a suitable method to increase the melt strength behavior of linear polypropylene (PP), which is a fundamental weakness of this material. This enables the modification of various properties of PP, which can then be used-in the case of PP recyclates-as a practical "upcycling" method. In this study, the effect of five different peroxides and their effectiveness in building LCB as well as the obtained mechanical properties were studied. A single screw extruder at different temperatures (180 and 240 °C) was used, and long-chain branched polypropylene (PP-LCB) was prepared via reactive extrusion by directly mixing the peroxides. The peroxides used were dimyristyl peroxydicarbonate (PODIC C126), tert-butylperoxy isopropylcarbonate (BIC), tert-Butylperoxy 2-ethylhexyl carbonate (BEC), tert-amylperoxy 2-ethylhexylcarbonate (AEC), and dilauroyl peroxide (LP), all with a concentration of 20 mmol/kg. The influence of the temperature on the competitive prevalent reactions of degradation and branching was documented via melt mass-flow rate (MFR), rheology measurements, and gel permeation chromatography (GPC). However, via extensional rheology, strain hardening could be observed in all cases and the mechanical properties could be maintained or even improved. Particularly, PODIC C126 and LP signaled a promising possibility for LCB in this study.