Tailored Bonded Interfacial Intermolecular Entanglement of Polyethylene/Ultrahigh-Molecular-Weight Polyethylene Blends: Enhancing Miscibility, Reinforcement, and Friction Reduction

On the Mechanical, Thermal, and Rheological Properties of Polyethylene/Ultra-High Molecular Weight Polypropylene Blends

The novel ultra-high molecular weight polypropylene (UHMWPP) as a dispersed component was melt blended with conventional high-density polyethylene (PE) and maleic anhydride grafted-polyethylene (mPE) in different proportions through a kneader. Ultra-high molecular weight polypropylene is a high-performance polymer material that has excellent mechanical properties and toughness compared to other polymers. Mechanical, thermal, and rheological properties were presented for various UHMWPP loadings, and correlations between mechanical and rheological properties were examined. Optimal comprehensive mechanical properties are achieved when the UHMWPP content reaches approximately 50 wt%, although the elongation properties do not match those of pure PE or mPE. However, it is worth noting that the elongation properties of these blends did not match those of PE or mPE. Particularly, for the PE/UHMWPP blends, a significant drop in tensile strength was observed as the UHMWPP content decreased (from 30.24 MPa for P50U50 to 13.12 MPa for P90U10). In contrast, the mPE/UHMWPP blends demonstrated only minimal changes in tensile strength (ranging from 29 MPa for mP50U50 to 24.64 MPa for mP90U10) as UHMWPP content varied. The storage modulus of the PE/UHMWPP blends increased drastically with the UHMWPP content due to the UHMWPP chain entanglements and rigidity. Additionally, we noted a substantial reduction in the melt index of the blend system when the UHMWPP content exceeded 10% by weight.

Mesoscopic Simulation for the Effect of Cross-Linking Reactions on the Drug Diffusion Properties in Microneedles

The drug diffusion issue in microneedles is the focus of its medical application. It will not only affect the distribution of drugs in the needle body but will also have an impact on the drug release performance of the microneedle. The utilization of cross-linked polymer materials to obtain the drug diffusion control has been experimentally verified as a feasible method. However, the mechanism research on the molecular level is still incomplete. In this study, the dissipative particle dynamics (DPD) simulation has been applied to study the effect of the cross-linking reaction on drug diffusion in hyaluronic acid microneedles. We have discovered that when the cross-linking degree reaches 90%, the diffusion coefficient of the drug is 6.45 times lower than that of the uncross-linked system. The main reason for the decline in drug diffusion ability is that the cross-linking reaction varies the conformation of the polymer. The amplification in the cross-linking degree makes the polymer coils more compact and approach each other, finally forming a continuously distributed cross-linked network, which reduces its degradation rate in the body. Simultaneously, these cross-linked networks can also hinder the interaction of soluble drugs with water, thereby preventing the premature release of drugs. The simulation results are consistent with the data collected in the previous microneedle experiment. This work will be an extension of DPD simulation in the application of biological materials.

Elongational Flow Field Processed Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends with Distinct Interlayer Phase for Enhanced Tribological Properties

Herein, we produced a series of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends by elongational-flow-field dominated eccentric rotor extruder (ERE) and shear-flow-field dominated twin screw extruder (TSE) respectively and presented a detailed comparative study on microstructures and tribological properties of UHMWPE/PP by different processing modes. Compared with the shear flow field in TSE, the elongational flow field in ERE facilitates the dispersion of PP in the UHMWPE matrix and promotes the interdiffusion of UHMWPE and PP molecular chains. For the first time, we discovered the presence of the interlayer phase in blends with different processing modes by using Raman mapping inspection. The elongational flow field introduces strong interaction to enable excellent compatibility of UHMWPE and PP and induces more pronounced interlayer phase with respect to the shear flow field, eventually endowing UHMWPE/PP with improved wear resistance. The optimized UHMWPE/PP (85/15) blend processed by ERE displayed higher tensile strength (25.3 MPa), higher elongation at break (341.77%) and lower wear loss of ERE-85/15 (1.5 mg) compared to the blend created by TSE. By systematically investigating the microstructures and mechanical properties of blends, we found that with increased content of PP, the wear mechanism of blends varies from abrasive wear, fatigue wear, to adhesion wear as the dominant mechanism for two processing modes.