Long chain branched polyethylene (LCBPE) without gel was prepared by melt branching reaction in a Haake torque rheometer in the presence of peroxide and different multi-functional acrylate monomers, and the optimal reaction time was determined according to the transient torque curves. The Fourier transform infrared (FTIR) results indicated that multi-functional monomers had been grafted onto HDPE backbone. Rheometer, ¹³C NMR, and high-temperature gel permeation chromatography (HT-GPC) coupled with triple detectors were used to characterize the microstructure of the LCBPE. The results showed the LCB content and the degree of branching increased with the increasing of functionality of the multi-functional monomers. Moreover, the LCBPE samples exhibited higher apparent zero shear rate activation energy and clear strain-hardening behavior compared with pure HDPE. Various rheological plots including viscosity, storage modulus, loss angle, and Cole-Cole plots were used to distinguish LCBPE from linear HDPE. A possible mechanism for melt branching reaction was also discussed in this paper. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were used to study the influences of LCB on the crystallization behavior and crystal morphology of all samples. It was found that the melt temperature and crystal morphologies of LCBPE were evidently different from that of pure HDPE due to the introduction of LCB.

The outstanding diffusivity and permeability of supercritical carbon dioxide (scCO₂) are extremely beneficial for grafting reaction. In this work, aramid fibers (AF) are modified in scCO₂ by glycidyl-polyhedral oliomeric silsesquioxane (POSS) with 2-ethyl-4-methylimidazole (2E4MZ) on the basis of cleaning with acetone. The surface morphology and chemical structure of the modified AF were measured and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Thermogravimetric (TG), and Atomic force microscope (AFM). The interfacial shear strength (IFSS) was measured by a micro-bond pull-out test, then the modified AF/EP composites were prepared and the interlaminar shear strength (ILSS) was characterized. Research has shown that some of the glycidyl-POSS molecular chains permeated into the surface of the fiber and grafted onto the surface of the AF after modification, and the other glycidyl-POSS self-assembled on the surface of the fiber. XPS indicated the introduction of C–O and –COO–, which confirmed the existence of chemical reactions between AF and glycidyl-POSS. AFM and SEM images revealed that 2E4MZ, not only promoted the grafting reaction of glycidyl-POSS, but also intensified the self-assembly of glycidyl-POSS, both of which increased the roughness of the fiber. A monofilament tensile test and micro-bond pull-out test showed that there was a negative effect on the tensile strength after scCO₂ processing. The tensile strength of modified AF, with glycidyl-POSS, increased the highest strength of 25.7 cN dtex⁻¹, which was 8% higher than that of pristine AF. The improvement of ILS roughness and the polar chemical groups produced in grafting reaction. These results indicated that AF, treated in scCO₂, with glycidyl-POSS, which is a suitable way of fiber modification, can significantly improve the surface adhesion of AF reinforced composites.

Long chain branched poly (lactic acid) (LCBPLA) was prepared via transesterification between high molecular weight poly (lactic acid) (PLA) and low molar mass monomer trimethylolpropane triacrylate (TMPTA) during melt blending in the presence of zinc oxide nanoparticles (nano-ZnO) as a transesterification accelerant in a torque rheometer. Compared with the traditional processing methods, this novel way is high-efficiency, environmentally friendly, and gel-free. The results revealed that chain restructuring reactions occurred and TMPTA was grafted onto the PLA backbone. The topological structures of LCBPLA were verified and investigated in detail. It was found that the concentration of the accelerants and the sampling occasion had very important roles in the occurrence of branching structures. When the nano-ZnO dosage was 0.4 phr and PLA was sampled at the time corresponding to the reaction peak in the torque curve, PLA exhibited a star-shaped topological structure with a high branching degree which could obviously affect the melt strength, extrusion foaming performances, and crystallization behaviors. Compared with pristine PLA, LCBPLA showed a higher melt strength, smaller cell diameter, and slower crystallization speed owing to the synergistic effects of nano-ZnO and the long chain branches introduced by the transesterification reaction in the system. However, severe degradation of the LCBPLAs would take place under a mixing time that was too long and lots of short linear chains generated due to the excessive transesterification reaction, with a sharp decline in melt strength.