查看更多>>摘要：Since electromagnetic pollution is detrimental to human health and the environment,numerous efforts have been successively made to achieve excellent electromagnetic interference shielding effectiveness(EMI SE)via designing the hierarchical structures for electromagnetic interference(EMI)shielding polymer composites.Among the plentiful structures,the asymmetric structures are currently a hot spot,principally categorizing into multi-layered,porous,fibrous,and segregated asymmetric structures,which endows the high EMI shielding performance for polymer composites incorporated with magnetic,conductive,and/or dielectric micro/nano-fillers,due to the"absorption-reflection-reabsorp-tion"shielding mechanism.Therefore,this review provides the retrospection and summary of the efforts with respect to abundant asymmetric structures and multifunctional micro/nano-fillers for enhancing EMI shielding properties,which is conducive to the booming development of polymeric EMI shielding materials for the promising prospect in modern electronics and 5-generation(5G)technology.
查看更多>>摘要：The tacticity of vinyl polymers is a key factor affecting the properties of materials.Recently,organic Brønsted acids have been demon-strated as effective catalysts for the development of highly stereoselective cationic reversible addition-fragmentation chain transfer(RAFT)poly-merizations of vinyl ethers,in which the use of RAFT agents could allow the control the molecular weight and tacticity of polymer products simul-taneously.However,the effect of RAFT agents on the tacticity-regulation remains elusive and lacks of investigation.In this study,we synthesized four types of RAFT agents and evaluated their influence in the stereoselective cationic polymerization of isobutyl vinyl ether in the presence of PADI as a Brønsted acid catalyst,which unveils that the Z group of RAFT agents could not only affect the polydispersity of the products,but also exert a profound effect on the stereoselectivity.After extensive screening of the RAFT agents,high stereoregularity(isotacticity,90％m)was ob-tained when using dithiocarbonate ester-type RAFT agents with a benzyloxy Z group.
查看更多>>摘要：Bacterial biofilms present a significant challenge in treating drug-resistant infections,necessitating the development of innovative nanomedicines.In this study,we introduce triclosan-conjugated,lipase-responsive polymeric micelles designed to exploit biofilm properties and serve as a responsive drug delivery platform.The micelles were created using an amphiphilic block polymer synthesized via ring-opening poly-merization of e-caprolactone(CL)and triclosan-containing cyclic trimethylene carbonate(MTC-Tri).Poly(ethylene glycol)(PEG-OH)acted as the macro-initiator,resulting in micelles with a PEG shell that facilitated their penetration into bacterial biofilms.An important advantage of our mi-celles lies in their interaction with local bacterial lipases within biofilms.These lipases triggered rapid micelle degradation,releasing triclosan in a controlled manner.This liberated triclosan effectively eliminated bacteria embedded in the biofilms.Notably,the triclosan-conjugated micelles displayed minimal toxicity to murine fibroblasts,indicating their biocompatibility and safety.This finding emphasizes the potential application of these micelles in combatting drug resistance observed in bacterial biofilms.Our triclosan-conjugated,lipase-responsive polymeric micelles ex-hibit promising characteristics for addressing drug resistance in bacterial biofilms.By harnessing biofilm properties and implementing a respon-sive drug delivery system,we seek to provide an effective solution in the fight against drug-resistant bacteria.
查看更多>>摘要：Against the backdrop of a global paper resource shortage,there is a growing need to identify fast-growing tree species capable of pro-ducing long-lasting paper.Three plant species namely Broussonetia kazinoki,Broussonetia papyrifera and hybrid paper mulberry,belong to the Broussonetia genus,were collected from China to study their white bark suitability for pulp and papermaking.Their chemical composition re-vealed that the holocellulose content in Broussonetia kazinoki and Broussonetia papyrifera was more than 80％.The molecular weight distribution of several holocellulose/a-cellulose is observed by GPC,which allows us to better observe the changes of various components on the molecular weight.The yield,lignin,whiteness,and molecular weight of the pulps obtained by NaOH treatment were determined.Optical microscope was used to characterize the fiber length-width ratio and rigidity.Finally,the improvement of the fiber rigidity method based on the Kratky-Porod chain model makes it more theoretical and further reveals the influencing factors of fiber rigidity.This study demonstrates the high potentiality of these three species for papermaking applications.
查看更多>>摘要：Poly(lactide acid)(PLA)foams have shown considerable promise as eco-friendly alternatives to nondegradable plastic foams,such as polystyrene(PS)foams.Nevertheless,PLA foam typically suffers from low heat-resistance and poor cellular structure stemming from its inherent slow crystallization rate and low melt strength.In this study,a high-performance PLA foam with well-defined cell morphology,exceptional strength and enhanced heat-resistance was successfully fabricated via a core-back microcellular injection molding(MIM)process.Differential scanning calorimetry(DSC)results revealed that the added hydrazine-based nucleating agent(HNA)significantly increased the crystallization temperature and accelerated the crystallization process of PLA.Remarkably,the addition of a 1.5 wt％of HNA led to a significant reduction in PLA's cell size,from 43.5 μm to 2.87 μm,and a remarkable increase in cell density,from 1.08x107 cells/cm3 to 2.15x1010 cells/cm3.This enhance-ment resulted in a final crystallinity of approximately 55.7％for the PLA blend foam,a marked improvement compared to the pure PLA foam.Fur-thermore,at 1.5 wt％HNA concentration,the tensile strength and tensile toughness of PLA blend foams demonstrated remarkable improve-ments of 136％and 463％,respectively.Additionally,the Vicat softening temperature of PLA blend foam increased significantly to 134.8 ℃,whereas the pure PLA foam exhibited only about 59.7 ℃.These findings underscore the potential for the preparation of lightweight injection-molded PLA foam with enhanced toughness and heat-resistance,which offers a viable approach for the production of high-performance PLA foams suitable for large-scale applications.
查看更多>>摘要：In this study,a series of hindered urea bond(HUB)containing polyurethane-urea methacrylate prepolymers and a none HUB contain-ing polyurethane methacrylate prepolymer were prepared using isobornyl methacrylate as the reactive diluent via one-pot procedure.The pre-polymers were characterized fully by various techniques.Then,their thermosets were fabricated via UV curing in presence of a photo initiator,and their mechanical property and thermal behavior were investigated and compared.Different from the none HUB containing thermoset,the HUB containing thermosets(defined as PUT)could be recycled and reprocessed by hot press under relatively mild conditions with high recovery ratio of mechanical property.Furthermore,zinc oxide(ZnO)nanoparticles were modified with 3-(trimethoxysilyl)propyl methacrylate and the modified ZnO(defined as ZnO-TPM)was dispersed and polymerized into PUT matrix to prepare their nanocomposites.The influence of ZnO-TPM on the mechanical performance of the composites was evaluated,which indicated that the Young's modulus and tensile strength increased grad-ually to the maximum values at ZnO-TPM content of 1 wt％and then decreased.The composites also displayed good reprocessability with im-proved recovery ratio compared to the pure PUT sample.In addition,the composite materials exhibited strong UV absorption capacity,implying their potential application in the circumstance where UV-shielding was required.
查看更多>>摘要：Inkjet 3D printing has potential in the additive manufacturing of electronic circuits and devices.However,inks that can be used for printing layers with T5％＞300 ℃ or hardness＞200 MPa have been rarely reported.Cyanate ester(CE)polymers have excellent thermal stability,high strength,and low shrinkage compared to other common dielectric inks for inkjet 3D printing,but cannot be quickly shaped by ultraviolet(UV)irradiation or thermal treatment.Combining CEs with UV-curable monomers may be a possible way to accelerate crosslinking,but there are challenges from the adverse effects of the dilution of both monomers.In this study,dielectric inks with acrylate and cyanate moieties were devel-oped.The low viscosity and surface tension of the CE precursor(Bisphenol E cyanate ester)were combined with photocurable acrylate diluent monomers and cross-linker to realize an ink suitable for inkjet 3D printing.An internal dual three-dimensional cross-linked network structure resin was prepared by a combination of photocuring and thermal curing with T5％up to 326.69 ℃,hardness up to 431.84 MPa,dielectric constant of 2.70 at 8 GHz,and shrinkage of 1.64％.The developed dielectric inks can be applied to the 3D printing of printed circuit boards and other elec-tronic devices that require dielectric properties.
查看更多>>摘要：For a polymer/polymer dismissible blend with two crystallizable components,the crystallization behavior of different components and the reciprocal influences between different crystals are interesting and important,but did not investigate in detail.In this study,the L-poly(lactic acid)/polypropylene(PLLA/PP)blends with different weight ratios were prepared by melt mixing and the crystallization behavior of the blends were investigated.Results showed that the crystalline structures of PLLA and PP were not altered by the composition.For the crystallization of PLLA,both the diffusion of chain segments and crystallization rate were enhanced under the existence of PP crystals.For the crystallization of PP,its crystallization rate was depressed under the existence of amorphous PLLA molecular chains.When the PP crystallized from the existence of PLLA crystals,although the diffusion rate of PP was reduced by PLLA crystals,the nucleation positions were obviously enhanced,which accelerat-ed the formation of PP crystals.This investigation would supply more basic data for the application of PLLA/PP blend.
查看更多>>摘要：Various sectors of the industry are searching for new materials with specific requirements,providing improved properties.The study presents novel composite materials based on polylactide that have been modified with the organosilicon compound,(3-thiopropyl)polysilsesquioxane(SSQ-SH).The SSQ-SH compound is a mixture of cage structures and not fully condensed random structures.The composite materials were obtained through injection moulding.The study includes a comprehensive characterization of the new materials that analyze their functional properties,such as rheology(MFR),mechanical strength(tensile strength,Charpy impact strength),and thermal properties.SEM microscopic photos were also taken to analyze the microstructure of the samples.The addition of a 5％by-weight organosilicon compound to polylactide resulted in a significant increase in MFR by 73.8％compared to the neat polymer.The greatest improvement in impact strength was achieved for the 5％SSQ-SH/PLA composite,increasing it by 32.0 kJ/m2 compared to PLA,which represents an increase of up to 187％.The con-ducted research confirms the possibility of modifying the properties of the polymer by employing organosilicon compounds.
查看更多>>摘要：Regulation of phase structure has been recognized as one of the most effective ways to fabricate self-healing polymers with high me-chanical strength.The mechanical properties of the resultant polymers are certainly affected by the size of separated phase domain.However,the study on this aspect is absence,because it can hardly exclude the influence of variation in monomer proportion required for tuning the sepa-rated phase size.Here,we report the first study on tuning the phase size through reversible addition-fragmentation chain transfer(RAFT)poly-merization without changing the proportion of monomers.As expected,the size of separated phase has been successfully mediated from 15 nm to 9 nm by tuning the molecular weight of the chain transfer agent.It is found that the mechanical strength and the self-healing efficiency of the resultant polymers increase simultaneously with the decrease of phase size.The study on the formation kinetics of hydrogen bonds reveals that the decrease of phase size can facilitate the re-bonding rate of hydrogen bonds,even if the migration of polymer chains is restricted.
万方数据
维普