| Owing to its excellent mechanical properties,polyurethane?PU?has increasingly been used during the past thirty years in the textile industry and a variety of other applications,such as national defense,transportation,medical market,sports,and energy industry,which are of great importance to the national economy.In order to expand the application of polyurethane in the textile field,the mechanical properties of polyurethane should be improved.Conventional methods for the preparation of high toughness of PU includes the chemical modification,physical regulation and adding organic or inorganic particles into PU,respectively.However,there are several drawbacks to these methods.Firstly,the chemical modification has shortcomings such as complicated steps,high cost,restricted modification effect.Secondly,although the mechanical properties of PU can be enhanced using the physical regulation methods,it is difficult to further optimize its improvement.Therefore,the optimization of the mechanical properties of PU is of great significance.Additionally,the surface modification of nanoparticles is complex and costly,which restricts the fabrication of a mechanical enhanced polymeric nanocomposite at a large scale.In addition,the high surface area of filler leads to the poor interfacial interaction between fillers and polyurethane,resulting in poor mechanical properties of PU composites.Thusly,the development of a novel approach for the preparation of PU and its composites with excellent mechanical properties without damage the performance of fillers is beneficial to the application of polyurethane and its composites in the textile industry.In this study,the effects of different binary solvents on the forming process of PU films and regulation of PU chains were systematically investigated on the basis of the invariant chemical composition of PU.Further,the toughening mechanisms of PU films were studied to understand its nature and structure.Finally,unmodified particles were used to prepare the PU composites.The enhancement effect of the concentration of particles on the mechanical property of the PU composites was investigated.The conclusions were summarized as follows:?1?A HIPSE method was adopted to fabricate PU films using different binary solvents?DMF and different second solvents?.Outstanding mechanical properties of PU films were achieved using TOL/DMF binary solvent compared with the other binary solvents.Results showed that the films obtained using 40%TOL/DMF binary solvent show dense morphology and best mechanical properties.The highest tensile stress,strain,and toughness of PU-?TOL/DMF?-40 films were increased correspondingly by 711.88%,182.55%,and 1884.64%compared with those of PU-DMF film,respectively.The mechanisms of the film forming process were studied.The unique morphology of PU chains of PU-?TOL/DMF?-40 film may be ascribed to the TOL/DMF binary solvents.PU-?TOL/DMF?-40 with compactly arranged molecular chains can bigger deformation without breaking.Also,a higher packing density of PU chains,bigger number“N”,provides more energy dissipation chains to sustain the deformation without breaking.Thusly,the final breaking elongation of PU-?TOL/DMF?-40 was greatly improved compared with that of PU-DMF.Furthermore,the mechanical properties of PU films prepared by HIPSE method with different chemical structures were compared and analyzed.Results showed that HIPSE method could not only toughen PU 1185A,but also toughen other types of PU.The chemical structures for other types of PU are as follows:polyether PU with MDI and PTMG;polyether PU with HDI and PTMG;The strain of PU fabricated using HIPSE method was superior to those prepared using IP and IE methods.?2?Unmodified fibroin powder made from silk waste?SF?was successfully dispersed into the polyurethane?PU?via hybrid immersion precipitation and solvent evaporation?HIPSE?.The incorporation of 50 wt.%SF into PU3?HIPS?resulted in high strain of 1254.3±106.4%,exhibiting a 145.1%and 11733.0%increment from PU1-50%SF?immersion precipitation?and PU2-50%SF?solvent evaporation?,respectively.In addition,the incorporation of 50 wt.%SF into PU3?HIPSE?resulted in high toughness values of 54.9±0.4 MJ·m-3,exhibiting a 1670.9%and 6000.0%increment from PU1-50%SF?immersion precipitation?and PU2-50%SF?solvent evaporation?,respectively.The prepared PU and PU/SF composite films were then subjected to FTIR and XRD analysis.Results confirmed that the original structure of SF is well preserved in the PU/SF composite films.To reveal the reasons for the outstanding mechanical properties of PU3-50%SF,the SF distribution and the interfacial interaction between SF and the PU matrix were investigated using the original cross-sectional morphologies without damage.The excellent mechanical properties of PU3-50%SF?HIPSE method?can be attributed to the unique structure of the fibril bundle with reinforced connections that lead to more effective interfacial stress transfer between the SF and PU3 matrix.?3?Unmodified carbon nanotube was successfully dispersed into PU via HIPSE method.Prepared PU/CNT composites films were then subjected to mechanical property analysis.When the concentration of CNT was 10 wt.%,the stress,strain,and toughness of PU/CNT obtained using HIPSE methods?40%TOL/DMF binary solvents?were increased correspondingly by 122.50%,200.00%,and 667.26%compared with those of PU/CNT film obtained using the immersion precipitation method?DMF solvent?,respectively.In addition,the PU/CNT fabricated by HIPSE methods still exhibited good mechanical properties when the concentration of CNT was up to 30 wt.%.To reveal the reasons for the outstanding mechanical properties of PU/CNT fabricated using HIPSE method,the CNT distribution and the interfacial interaction between CNT and the PU matrix were investigated by the original cross-sectional morphologies without damage.The results suggested that the excellent mechanical properties could be ascribed to the unique fiber bundles of PU/CNT composites,the good interfacial interaction between CNT and the PU matrix,and the toughening mechanism induced by the crack bridging,microcrack and pulled-out during stretching.Further,the FTIR and XRD results showed that the structure of PU was not changed and the degree of microphase separation could be enhanced by adding the high content of CNT.Moreover,the thermal stability of PU/CNT composites was dramatically improved,exhibiting an increase in decomposition temperature by 25°C.When the content of CNT was 30 wt.%,the specific resistance of PU/CNT film was only 0.70?·cm.Most importantly,the PU/CNT film also exhibited good conductivity under a strain of 200%,indicating that the PU/CNT film can be used for the applications of monitor and sensor.?4?Unmodified ZrO2 nanoparticles?ZDNP?are used for the enhancement of polyurethane?PU?films.Optimized strain and toughness of PU/ZDNP nanocomposite at a 9.09 wt.%ZDNPs are up to 2714.6%,and 280.78 MJ·m-3,respectively.The unique bimodal ZDNP aggregates size distribution which exploits both interfacial positively and negatively toughening mechanisms accounts mainly for the excellent mechanical property of PU/ZDNP nanocomposite.The dependence of different toughening mechanisms on three sizes of ZDNP aggregates is summarized.These findings provide a new avenue for the industrial production of nanocomposites at low cost without surface modification of inorganic nanoparticles.FTIR and XRD results showed that the structure of PU was not changed and the degree of microphase separation could be enhanced by adding the high content of ZDNP.Furthermore,the thermal stability of PU/ZDNP composites was considerably improved,exhibiting an increase in decomposition temperature by 20°C.Additionally,the UVA and UVB transmittance of PU/ZDNP films was decreased from 95.15%to 7.78%and 12.84%to 0.24%,respectively,showing good UV radiation performance.Moreover,the toughening mechanism of PU/ZDNP films was further investigated by SEM,and the results showed that different size of ZDNP aggregates could be effectively dissipated the extra energy by an interfacial force positively correlated toughening mechanism,such as crack deflection and crack bridging,and the interfacial force negatively correlated toughening mechanism,such as microcrack and pulled-out.?5?The ultrahigh molecular weight polyethylene?UHMWPE?coated fibers,UHMWPE plain weave fabrics,and UHMWPE coated fabrics were fabricated according to the optimization of TOL/DMF,PU/DMF,PU/CNT,and PU/ZDNP ratios.The effects of different PU composite solutions on the mechanical properties of UHMWPE coated fibers were studied,and the results showed that the breaking strength of these fibers could be significantly enhanced.Compared with UHMWPE fibers,the PU/ZDNP coated UHMWPE fibers showed an improvement on the breaking strength and breaking elongation by 110.36%and 62.83%,respectively.Furthermore,the mechanical properties of UHMWPE plain weave fabrics fabricated using the UHMWPE coated fibers were studied,and the results suggested that compared with the UHMWPE plain weave fabrics fabricated using immersion precipitation method,the UHMWPE plain weave fabrics fabricated using HIPSE method exhibited an enhanced breaking strength.Additionally,the mechanical property results showed that the breaking strength and breaking elongation of UHMWPE coated fabrics could be considerably enhanced.The fracture of UHMWPE coatings is divided into two stages:the first stage is the detachment of warp and weft yarns,and the second stage is the rupture of PU and its composites.Moreover,the UHMWPE coated fabrics fabricated using HIPSE exhibited the good interfacial force between PU composites and UHMWPE.According to the above studies,high concentrations of SF,CNT,and ZDNP make the UHMWPE fibers and fabric functionality,such as comfortability,thermal stability,electrical conductivity,and ultraviolet resistance.This provides a good application prospect of UHMWPE fabrics. |
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