Free-radical reactions of polymers, including biodegradable polymers via reactive extrusion, are normally induced by peroxide chemicals, which are known to lead to the formation of secondary products and impart some performances to the resin. Here, we report an ultraviolet (UV)-induced reactive extrusion, without employing a peroxide initiator, to control chain scission and branching reactions of polylactide (PLA). Through this technique, chain scission reaction of molten PLA induced by UV irradiation during extrusion was promoted to high-level efficiency. Degraded PLA samples had lower complex viscosity and storage modulus, because of random main chain scissions. Long-chain branched (LCB) structure of PLA was obtained when a multifunctional chemical agent, trimethylolpropane triacrylate (TMPTA), was added into the PLA matrix during extrusion. Various rheological plots including viscosity, storage modulus, loss tangent, and Cole–Cole plots were used to distinguish the LCB structures of PLA samples. Thermal and crystallization properties of degraded and branched PLA samples were also investigated by means of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). For the LCB PLA samples, a distinct crystallization exothermic peak appeared and accompanied by the disappearance of the cold crystallization temperature, demonstrating significantly enhanced crystallization rates. This UV-induced reactive extrusion has nonresidues of peroxide, is highly efficient and easily adjustable, and opens new avenues in potential applications for PLA modification, such as grafting and polymerization.

In this work, rapid ozone degradation of polypropylene (PP) was developed for the aim of rheology control using a reactive extrusion process. Experiments were carried out in a co-rotating intermeshed twin-screw extruder with varied polymer throughput and reaction temperature. Ozone was introduced into the extruder to rapidly oxidize molten PP in just several seconds period. The oxidized PP was characterized through melt flow index (MFI), rheological measurement, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy tests. The influence of reactive temperature and polymer throughput on the degradation reaction was studied. It was noted that molten PP could be fast and successfully degraded during this reactive extrusion process. The oxidized PP had higher MFI than that of the origin PP resin, indicating the decrease of molecular weight of PP. Carbonyl groups were formed on the PP molecular chains. This rapid oxidization process has higher reaction efficiency than the ozone degradation of PP in solid state and no harmful byproduct would be generated from this ozonizing reaction.

Deeply oxidization of waster rubber crumb (WRC) by ozone treatment was carried out at room temperature with long time exposure. Gel content measurement, TG/DTG (thermogravimetric) analysis, ATR-FTIR (attenuated total reflectance-Fourier transform infrared) spectroscopy, XPS (X-ray photoelectron spectroscopy) and mixing properties tests were used to investigate the structure and properties of deeply oxidized WRC. After ozone oxidation, the gel content of WRC decreased dramatically in the first 3 h and then decreased slowly with prolonging the oxidation time. TG/DTG results showed that few low molecule weight materials were produced although ozone did destroy some cross-linking networks by oxidizing decomposition. ATR-FTIR and XPS spectrum showed the increase of oxygen-containing groups in WRC, indicating that oxidation reaction between ozone and WRC happened. Deeply oxidized WRC could form a uniform plate under pressure and heat due to regaining part of the flowability.

Cross-linked poly(butylene succinate) (PBS) was prepared by the reactions of the end hydroxyl groups of PBS with toluene diisocyanate and trimethylolpropane (TDI–TMP) polyurethane prepolymer at the processing temperature. The effects of varied TDI–TMP prepolymers on properties such as mechanical properties, thermal properties, dynamic mechanical properties, and crystal morphology were investigated. The results indicated that TDI–TMP prepolymer could cross-link PBS with high efficiency. The gel fraction of the cross-linked PBS increased with the content of TDI–TMP prepolymer, and the melt flow index of PBS decreased. Differential scanning calorimetry and dynamic mechanical analysis revealed that the crystallization temperature and glass transition temperature increased with the content of the TDI–TMP prepolymer, while the melting points and degree of relative crystallinity decreased. The cross-linked PBS also showed improved tensile properties, impact properties, thermal stability, and dynamic mechanical properties.

A novel single screw extruder, with high transparent quartz glass as barrel, was employed to carry out reactive extrusion for ultrafast photo degrading molten polypropylene (PP). Ultraviolet (UV) was adopted to irradiate the molten PP to induce radical reaction and hereby to degrade PP macromolecules during extrusion. Compared with photo degradation of PP in solid state, reaction efficiency and uniformity in this process were greatly improved. Reactive degree was controlled by varying screw speed and photo-sensitizer (benzophenone, BP) concentrations. The structure and properties of degraded polypropylene was characterized by melt flow rate (MFR), Fourier Transform Infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) and tensile properties test. After extrusion with UV irradiation, the melt flow rate increased and crystallization temperature decreased of the degraded samples. FT-IR showed no obvious CO groups were formed in molecular structure, indicating the oxidation reaction was very minimal.