Journal of Polymer Science最新文献

Cellulose nanocrystal (CNC)-reinforced composites are gaining commercial attention on account of their high strength and sustainable sourcing. Grafting polymers to the CNCs in these composites has the potential to improve their properties, but current solution-based synthesis methods limit their production at scale. Utilizing dynamic hindered urea chemistry, a new method for the melt-functionalization of cellulose nanocrystals has been developed. This method does not require toxic solvents during the grafting step and can achieve grafting densities competitive with state-of-the-art solution-based grafting methods. Using cotton-sourced, TEMPO-oxidized CNCs, multiple molecular weights of poly(ethylene glycol) (PEG) as well as dodecane, polycaprolactone, and poly(butyl acrylate) were grafted to the CNC surface. With PEG-grafted nanoparticles, grafting densities of 0.47 chains nm⁻² and 0.10 chains nm⁻² were achieved with 2000 and 10,000 g mol⁻¹ polymer chains respectively, both of which represent significant improvements over previous reports for solution-based PEG grafting onto CNCs.

The structure, morphology, and performance of polyurethanes are greatly influenced by the structure of chain extenders. In this study, two types of amine chain extenders, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (BAPD) and isophorone diamine (IPDA), were utilized in the synthesis of poly(dimethylsiloxane) (PDMS)-based poly(urea-urethane) elastomers (PDMS-PUUs). The mechanical properties, morphology, and in vitro oxidative stability of the as-prepared elastomers were controlled by altering the ratio of BAPD and IPDA. The results indicate that the overall phase mixing of PDMS-PUUs improves after incorporating of BAPD into the hard segments. The hard segment, composed of IPDA with a rigid structure, plays a crucial role in maintaining the essential mechanical properties of the PDMS-PUUs. Furthermore, PDMS-PUUs based on mixed chain extenders exhibit relatively high boundary diffuseness and boundary thickness. Especially, the PDMS-PUU sample synthesized from BAPD and IPDA with a molar ratio of 1/1 features the highest boundary diffuseness (0.094) and boundary thickness (0.395 nm), consequently displaying some remarkable properties, including enhanced cyclic tensile properties, superior strain recovery (92.6%), a low modulus (8.6 MPa), and high tensile strength (20.3 MPa). PDMS-PUUs also exhibit good oxidative stability and biocompatibility, implying that the as-prepared PDMS-PUUs are proven to be biostable and capable of long-term implantation.

The exothermic nature of acrylate photopolymerizations enables room temperature 3D printing of a quaternary formulation that incorporates an acrylate monomer, and an epoxy/thiol-ene system (ETES). The latter comprises an epoxy monomer, a multifunctional thiol and a tetraallyl functionalized ditertiary amine curing agent. Pristine ETES necessitates temperatures of 85–95 °C for curing. Several mechanisms operate simultaneously during this process: homopolymerization of acrylates, thiol-acrylate photopolymerization, thiol-ene photopolymerization between the double bonds of curing agent and the multifunctional thiol, the Michael addition between thiolates derived from ETES and the double bonds of acrylates, and the anionic polymerization of the epoxy resin via the tertiary amine groups. To optimize the quaternary formulations for printing, parameters, such as reactivity, exothermicity, and viscosity, was explored. Subsequently, the thermal and viscoelastic properties of the printed cross-linked polymers derived from these formulations were analyzed using Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). The polymers derived from quaternary formulations exhibited lower crosslinked density compared to those obtained from the pristine acrylates. This reduction in crosslink density contributes to the improved toughness of the hybrid polymers.

Cellulose acetate (CA), synthesized by solid–liquid acetylation of low crystalline cellulose (LCCell) obtained by cold shearing in a short time under environmentally benign conditions, effectively enhanced the crystallization of poly(lactic acid) (PLA). The composite of PLA compounded with CA from LCCell exhibited higher crystallinity of PLA and flexural modulus than those from pristine PLA. CAs obtained from crystalline and recrystallized cellulose also improved the mechanical strength of PLA by compounding, but their effects were weaker than that of CA from LCCell. The factor of the effectiveness of CA obtained from LCCell is the higher miscibility with PLA originating from the sufficiently released interchain hydrogen bonds in the cellulose fibrils by cold shearing, which allows the dissolution of macroscopic aggregation of the CA chains in the composite.

Firefighters' protective clothing rely on moisture barriers to safeguard against liquid ingress while enabling sweat evaporation for comfort and safety. However, these moisture barriers can degrade over time, jeopardizing firefighters' safety. Existing evaluation methods, primarily visual inspection, are inadequate for assessing moisture barrier integrity in service. This study examines the effect of accelerated hydrothermal aging on the tear force, water vapor transmission rate (WVTR), and apparent contact angle in three moisture barrier models used in firefighter protective clothing. The moisture barriers studied varied in composition, structure, and base fabric fiber content. Results revealed that moisture barriers' responses to aging are influenced by factors, such as fabric structure, adhesive configuration, finish, and the presence of additional coatings. The hardening of the adhesive layer between the ePTFE membrane and the base fabric was observed in two of the moisture barriers, leading to a slight tear force reduction. Two of the moisture barriers also experienced crack and pit formation on the membrane side, which affected the WVTR. The water-repellent finish on the fabric side degraded in one moisture barrier. Understanding these complex behaviors is essential for predicting the long-term moisture barrier performance and enhancing firefighter safety.

Functional polyvinylethylene glycols (PVEGs) with pendent vinyl groups were synthesized by Pd/B synergistic catalysts and their structures were characterized by ¹H NMR and FT-IR. The photopolymerization of the obtained PVEGs with multifunctional thiols in the presence of a photoinitiator proceeded smoothly via thiol-ene photo-click reaction to give a series of crosslinked materials by the variation of the molecular weight of PVEGs and a ratio of thiols and enes. The curing behavior was studied by FT-IR and the properties of crosslinked materials were characterized by the test of gel content, swelling ratio, and water absorption. The dynamic mechanical analysis, mechanical properties, thermogravimetry, and surface properties of the crosslinked materials were investigated and the performance of coating for the crosslinked film materials was also characterized. The crosslinked film materials can be further functionalized by post-crosslinking modification through thiol-ene photo-click reaction.

As a soft material with biocompatibility and stimulation response, ionic conductive hydrogel-based wearable strain sensors show great potential across a wide spectrum of engineering disciplines, but their mechanical toughness is limited in practical applications. In this study, freeze-thawing techniques were utilized to fabricate double-network hydrogels of poly(vinyl alcohol)/polyacrylamide (PVA/PAM) with both covalent and physical cross-linking networks. These double-network hydrogels demonstrate excellent mechanical performance, with an elongation at break of 2253% and tensile strength of 268.2 kPa. Simultaneously, they also display a high sensitivity (Gage factor, GF = 2.32 at 0%–200% strain), achieve a rapid response time of 368 ms without the addition of extra conductive fillers or ions, stable signal transmission even after multiple cycles, and fast response to human motion detection.

This study investigates the morphology and properties of biocomposites based on a blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly (lactic acid) (PLA) 50/50 (w/w) reinforced with untreated (UNDF) and alkali-treated (ATDF) Diss (Ampelodesmos mauritanicus) fibers at 20 wt. %. Moreover, PHBV-g-MA used as the compatibilizer was added at 5 wt. % to the alkali-treated biocomposites. Morphology, and crystallinity, thermal, thermo-mechanical, rheological and mechanical properties of PHBV/PLA biocomposites were studied. The study showed that the treated Diss fibers were uniformly dispersed in both PLA and PHBV phases. This results in a good interfacial adhesion between the components, as observed by scanning electron microscopy (SEM). Further, the results also indicated that the compatibilized biocomposite samples showed an enhancement in crystallinity degree and heat deflection temperature (HDT) passing from 48.7% to 62.4% and 119.2 to 132.9°C, respectively, in comparison with the neat blend. Similar trend is also observed with the tensile data indicating a significant increase in Young's modulus by almost 48.5% compared to PHBV/PLA matrix. This is due to better interactions between Diss fibers and PHBV/PLA matrix. The results suggest the occurrence of a synergistic effect between PHBV-g-MA and alkali-treated Diss fibers in the development of materials with interesting properties and could be a potential means to expand their applications.

In this work, two novel pyrimidine-cored covalent organic frameworks TpTap-COF and TpTan-COF were synthesized for the first time and used for the adsorption of heavy metal ions in aqueous solution. Both COFs are nanofiber clusters with preferable crystallinity and thermal stability. The impact parameters such as pH value, shaking time, initial concentration, and temperature were studied by batch adsorption experiments in the multi-metal ions system. The adsorption of six metal ions onto COFs follows the pseudo-second-order kinetic model and the Freundlich isotherm model, which is a chemical adsorption process that occurs on non-uniform surfaces. The adsorption rate is determined by both film diffusion and intraparticle diffusion. Further research on the adsorption of copper ions onto COFs indicates the formation of metal complexes between O#N#N/O#O chelating sites in the COF skeleton and Cu ions through the sharing of lone pair electrons.

Conjugated ladder polymers (cLPs) represent an intriguing class of macromolecules, characterized by their multi-stranded structure, with continuous fused π-conjugated rings forming the backbone. Isotope substitution, such as deuteration and carbon-13 labeling, offers unique approaches to address the significant challenges associated with elucidating the structure and solution phase dynamics of these polymers. For instance, selective deuteration can highlight parts of the polymer by controlling the scattering length density of specific molecular sections, thereby enhancing the contrast for neutron scattering experiments. In this context, deuteration of side-chains in cLPs represents a promising approach to uncover the elusive polymer physics properties of their backbone. The synthesis of two distinct types of cLPs with perdeuterated side-chains are reported here. During the synthesis, ¹³C isotope labeling was also employed to verify the low levels of defects in the synthesized polymers. Demonstrating these synthetic successes lays the foundation for rigorous characterization of the defects, conformation, and dynamics of cLPs.