Polymer最新文献

This study investigates the dispersion and compatibility of low-entangled “dis-entangled” UHMWPE (dis-UH) in a high-density polyethylene (HDPE) matrix using solvent-free melt-blending conditions and compares it with entangled UHMWPE (eUH) in the same matrix. The findings reveal that dis-UH/HDPE exhibits a significantly lower viscosity ratio than eUH/HDPE (1 and 4, respectively), indicating a lower critical capillary number (Ca_critical), thus enhanced dispersion and compatibility. Blends with varying dis-UH content up to 20 wt% show homogeneity, evidenced by DSC and SEM analysis, and demonstrate improved mechanical properties by 36 % in the maximum stress (σ_max) and 39 % in Young's modulus (E). Linear viscoelasticity assessments reveal that higher dis-UH content slow the dynamics and increase the apparent weight average molecular weight (M_w), consistent with previous reports for linear entangled PE. The zero-shear viscosity (${\eta }_0)$ scaling with M_w (η₀ $\propto$ M ⁿ) is adjusted for high polydispersity, yielding a transitional point in the scaling exponent (n) from 3.6 to 3 at a reptation number of entanglement segments (M_r/M_e) of ∼287, in line with theoretical predictions. To rationalize the success of the homogenization process, we propose a qualitative molecular picture inspired from the constraint release Rouse mechanism involved in the disorientation process of bi-disperse linear polymers. In the case of dis-UH/HDPE blends, with initially lower density of long-long entanglements within dis-UH, and the highest density of short-short entanglements within HDPE matrix, the formation of long-short entanglements between dis-UH and HDPE is facilitated, which results in successful homogenization process. In the contrary, the establishment of long-short entanglements in eUH/HDPE blends will require unwinding of the long-long entanglements, which holds a higher kinetic barrier compared to dis-UH/HDPE blends, leading to unsuccessful homogenization.

Through molecular dynamics simulations, we investigated the effects of temperature on the axial tensile behavior of ultra-high molecular weight polyethylene (UHMWPE) crystals, considering the combined effects of transverse compression, strain rate, and molecular weight. The effects of temperature over the range of 100 K to 450 K is shown to reduce the mechanical properties. Existing chain end defects facilitate chain sliding and induce stress concentration in adjacent molecules, thereby reducing the strength and modulus of crystals. Lower molecular weight and higher temperatures promote chain sliding, while higher transverse compression and increased strain rates inhibit chain sliding, resulting in higher properties. Additionally, higher temperatures increase stress concentration due to thermal vibrations, which induce localized high stress conditions within polyethylene chains. The transition of the failure mode from chain sliding to bond breakage occurs at strain rates between 10¹² s⁻¹ and 10¹³ s⁻¹, and is found to be independent of temperature, pressure, and molecular weight. The results are compared to the response of crystals without chain end defects. These insights contribute to a deeper understanding of the behavior of UHMWPE crystals under extreme loading conditions.

Meeting the criteria of performance and biocompatibility poses a significant challenge in developing polymeric nonwovens for biomedical and filtration purposes. Although non-isocyanate poly(carbonate-urethane)s (NIPCUs) made by transurethane polycondensation are emerging as non-toxic alternatives to isocyanate-based polyurethanes, their fibrous processing is scarce. Therefore, our work focused on preparing electrospun nonwovens from sustainable NIPCUs with an architecture tailored for high mechanical strength. Combining aromatic 4,4′-diphenylmethane bis(hydroxyalkyl carbamate) hard segments and soft oligocarbonate segments imparted strength and flexibility, while incorporating up to 29 wt % of CO₂ into the structure of the NIPCUs. Scanning electron microscopy showed that adjusted electrospinning parameters produced uniform, submicron fibers without defects. FT-IR and NMR spectroscopy confirmed their unchanged composition and molar mass (20–25 kg mol⁻¹) compared to the unprocessed NIPCUs. Differential scanning calorimetry and dynamic mechanical thermal analysis showed that the macromolecular arrangement induced during electrospinning was strongly dependent on the architecture of the polymer. The mechanical performance of the nonwovens, reaching tensile strength above 5 MPa and elongation at break up to 250 %, correlated to their morphological differences. Thus, appropriate modification of the structure and morphology of the NIPCU nonwovens allowed the production of CO₂-rich submicron fibers with high toughness and flexibility.

Leveraging xanthated cellulose nanofibers (XCNF) from a modified rayon process, this study explores their use as stabilizers in Pickering emulsion polymerization for nanocomposite production. XCNF was produced from softwood pulp through a xanthation process that utilized a reduced NaOH concentration of 8.5 %, lower than the typical rayon process, and was followed by mechanical defibrillation, resulting in fiber widths under 10 nm. Following the protective allylation of xanthate groups and hydrophobic modification, ¹H NMR analysis was conducted, revealing a xanthation degree of 0.144. When stored at 4 °C, a 0.5 wt% XCNF dispersion gelled by the fifth day, as confirmed by visual and rheological assessments. UV and TEM analyses indicated xanthate detachment and nanofiber aggregation over time, respectively. The addition of a low-temperature initiator to the XCNF-stabilized styrene-water emulsion enabled polymerization, yielding nanofiber-encapsulated polystyrene latex. This led to transparent sheets upon thermal pressing, demonstrating the potential of XCNF in developing polymer nanocomposites.

The hydrogen diffusivities of acrylonitrile butadiene rubber (NBR) composites with different types and contents of carbon black (CB) fillers were investigated in the exposure pressure range of 0.5–10 MPa using a volumetric analysis system. These measured diffusivities exhibited distinct pressure-dependent behavior. The diffusivities of unfilled NBR and NBR composites containing medium-thermal CB filler decreased from 39.7 $\times$ 10⁻¹¹ m²/s to 9.4 $\times$ 10⁻¹¹ m²/s as the pressure increased. On the other hand, the pressure-dependent diffusivities of NBR composites containing high-abrasion furnace, fast-extrusion furnace and semireinforcing furnace CB fillers revealed left-biased unimodal shaped curves, with peak values ranging from 19.7 $\times$ 10⁻¹¹ m²/s to 5.6 $\times$ 10⁻¹¹ m²/s. To model this observed behavior, the diffusion resistance theory with a heterogeneous NBR–CB composite and a fractal porous structure for H₂ was introduced. The theoretical parallel diffusion resistance model was found to coexist independently as the surface, Knudsen, and bulk diffusion phases. This theoretical multiphase modeling was applied to the measured diffusivities, determining diffusion resistance parameters for each phase. The obtained individual parametric characteristics for each diffusion were interpreted by considering the CB filler content and volume fraction of the filler. As a result, the diffusivities calculated by multiphase diffusion modeling were in quite agreement with the measured diffusivities for all investigated specimens, where the determined squared correlation coefficient (R²) by fitting process was in the range from 0.69 to 0.97.

In this study, the raw material of Japanese cypress wood (Platycladus orientalis (Linn.) Franco) was used and subjected to a series of treatment, including replacement of the water in wood by organic solvent, liquid UV-curable coating impregnation, surface coating removal, and UV curing. By this method, we innovatively produced a new type of transparent wood film which we refer to as “wood-texture transparent wood” (WTTW). WTTW retained the color, texture, and tactility of wood, while exhibiting a high transmittance of light and haze. Macroscopic and microscopic tests demonstrated that by removing the excess coating on the impregnated wood film surface, the microstructure and roughness of the wood surface could be successfully preserved, and the wood-like tactility of WTTW could be realized. WTTW exhibits better properties than those of the original wood, including a maximum light transmittance of 72.3 %, a haze of 72.3 % (at 550 nm), a tensile strength of 123.90 MPa in the longitudinal direction, a tensile strength of 6.64 MPa in the cross direction, and a hardness of 81.8 HD. In comparison to the traditional transparent wood, WTTW not only streamlines the preparation process, but also preserves the original wood texture, which aligns more closely with the tenets of green environmental protection and is more suitable for home decoration and privacy protection.

A plethora of polymers are excellent candidates that can be utilized to build various terahertz (THz) based systems for sensing and microfluidics. SU-8 is a versatile epoxy-based polymer with excellent properties, such as biocompatibility and good mechanical properties. Nevertheless, the impact of curing parameters on the THz absorption characteristics of SU-8 remains uncertain. This study explores the impact of various curing conditions on the THz absorption properties of SU-8. The aim is to establish a correlation between THz absorption and the polymer's cross-linking characteristics. Therefore, three key curing parameters have been examined: time, temperature, and ultraviolet (UV) exposure dose. The SU-8 samples that are cured under different conditions are examined using THz Time-Domain Spectroscopy (THz-TDS) to estimate the THz absorption coefficient. Next, the swelling experiment is conducted to evaluate the polymer cross-linking of the cured samples. The results show that curing conditions and, thus, cross-linking routines significantly influence THz wave propagation and attenuation within SU-8 samples. The findings recommended using an optimal curing dose for SU-8 spanning 1240 mJ/cm² to 1860 mJ/cm² which results in a relatively lower absorption coefficient while still maintaining a higher state of cross-linking. This research establishes a crucial link between SU-8 processing and its THz response. It can lay the foundation for tailored SU-8 polymer with optimized THz transmission for novel and customized biosensing and microfluidic devices.

Herein, two monomers MTPA and FTPA, and their corresponding polymers (PMTPA and PFTPA) based on a methyl-and fluoro-substituted triphenylamine were synthesized by Stille reaction and electropolymerization. MTPA exhibited the red-shift absorption and fluorescence emission spectra, and lower E_onset (0.53 V) compared with FTPA (0.57 V), which is beneficial to achieve high-quality polymers. The polymer films exhibited reversible color transition from yellow green to deep blue for PMPTA and from dark brown to light blue for PFTPA, respectively. In addition, both PMTPA and PFTPA films exhibited good optical contrasts of 36 % and 40 % at 1100 nm, respectively. The coloration efficiency and response times at 1100 nm are 196.4 C⁻¹ cm² with 0.6 s for PMTPA, and 160.9 C⁻¹ cm² with 1.4 s for PFTPA, respectively. These polymer films demonstrated excellent electrochemical property and electrochromic performance. These results will also provide a new strategy to rationally design the excellent electrochromic polymers based on the triphenylamine core.

In situ microfibrillar PA6/PLA composites (MFCs) with high strength and toughness were produced via a multistage stretching extrusion system. The PA6 microfibrils induced the growth of PLA crystals perpendicular to the PA6 microfibrils and significantly enhanced the mechanical properties of the MFCs. Notably, the PLA-9 sample with 9 wt% PA6 microfibrils achieved excellent tensile strength and elongation at break (79.1 MPa and 77.8 %, respectively), which were 1.3 and 13.4 times than those of neat PLA. During the tensile process, the PA6 microfibrils underwent plastic deformation accompanied by the detachment and fragmentation of the PLA lamellae.