【作者】 张恒；

【导师】 李宝光；

【作者基本信息】 云南大学 ， 材料物理与化学， 2019， 硕士

【摘要】 纳米颗粒分散在聚合物基质中形成的聚合物纳米复合材料(PNC),不但结合了聚合物和纳米材料的性能,通常还会使材料具有突出的新型性能或功能。PNC在食品工业、药物、电子设备等各方面都已有广泛的应用。然而,合成聚合物的单体一般是石油来源的,这导致了对石油资源的过度依赖和对环境的严重污染。淀粉、甲壳素、壳聚糖、纤维素、木质素和橡胶等天然高分子为基质的新型PNC具有优异的力学、透光、阻燃、阻气、生物活性、生物相容性和可生物降解等性能。层状双氢氧化物(Layered double hydroxides,LDHs)在溶剂中层离后,可形成具有较大比表面积的纳米片层,同时具有生物相容性,是增强聚合物性能的理想二维纳米材料。本论文从充分有效利用自然界中丰富的甲壳素和纤维素的角度出发,采用氢氧化钠/尿素溶剂体系,分别溶解LDHs、甲壳素和纤维素,将Mg/Al-LDHs的纳米片层作为纤维素和甲壳素的增强相,模仿天然纤维素中的纤维结晶相的力学增强机理,提高再生纤维素和甲壳素的力学性能。主要研究内容如下:采用尿素水解法合成了Mg/Al-LDHs(LDHs-hy),并在NaOH/尿素/水的溶液中成功的层离了 LDHs-hy,得到含有LDHs-hy二维纳米片层的胶体溶液。将LDHs-hy的胶体溶液与采用相同溶剂溶解的甲壳素的碱液混合,经铸模热压法制备了不同含量的LDHs-hy/甲壳素纳米复合材料(LHCHNF)。研究了不同LDHs-hy含量对甲壳素薄膜材料的力学性能、热稳定性、透气性和透光性的影响。结果表明,由于LDHs-hy纳米片层对甲壳素分子链运动的限制作用,降低了甲壳素的结晶程度。当LDHs-hy含量达到8%时,LDHs-hy在甲壳素基质中重堆垛。随着LDHs-hy含量增加,甲壳素的拉伸模量和拉伸强度逐渐增加,拉伸强度最大增加量达44.4%。LDHs-hy纳米片层的复合增加了甲壳素第三步热分解温度,增加了成炭量,降低了失水和CO2的降解时热释放量,同时降低了主链发生断裂和交联、芳香化时的热释放量,甲壳素的热稳定性能增强。当LDHs-hy含量在4%时,甲壳素的透气系数降低,阻隔气体性能增加。其次,对LDHs-hy/纤维素纳米复合体系进行了研究。将LDHs-hy层离在LiOH·H2O/尿素/水的溶液中,与采用相同溶剂溶解的纤维素碱液混合,经抽滤热压法制备了LDHs-hy/纤维素纳米复合材料(LCENF)。研究了不同含量的LDHs-hy对纤维素薄膜材料的力学性能、热稳定性和透光性的影响。结果表明,含量在0-8wt%范围时,LDHs-hy能够完全均匀的分散在纤维素基质中,没有发生纳米片层的重新堆垛。力学测试结果表明,当LCENF中LDHs-hy含量为2%时,拉伸强度从18.16MPa增加到50.22MPa,增加了176.5%。LDHs-hy含量大于2%时,LCENF的拉伸强度从50.22MPa逐渐减少到]3.26MPa。对LCENF的热分析表明,LDHs-hy纳米片层降低了纤维素第一步热分解的速率和第二步热分解的起始温度,增加了纤维素主链的第一步热裂解温度,并对高温下热氧化放热起到了阻碍作用。表明LDHs-hy纳米片层显著的增加纤维素的热稳定性。LCENF经过抛光后是透光性非常好的薄膜,透光率测试表明,在600nm波长处,不同含量LDHs-hy的LCENF的透光度在1.1到2.0之间,LDHs-hy对LCENF的透光度影响不大。当LDHs-hy含量达到10wt%时,LCENF的透光度达到最大值3.3。以上研究结果,为充分利用来源丰富、性能优良且廉价和环保的天然高分子,为制备天然高分子的纳米复合材料提供了可行的制备途径。为天然高分子为基质的纳米复合材料的性能和实际应用提供了实验基础。为促进天然高分子材料的开发和应用提供了研究基础。更多还原

【Abstract】 The polymer nanocomposites(PNC)formed by dispersing nanoparticles in a polymer matrix combine not only the properties of polymers and nanomaterials,but also often give the materials novel properties or functions.PNC has been widely used in food industry,pharmaceuticals,electronic equipment and other fields.However,the menomer for chemical synthesized polymers is generally prepared from oil fuels,which leads to excessive dependence on petroleum resources and serious environmental pollution.New type PNC based on natural polymers such as starch,chitin,chitosan,cellulose,lignin and rubber have excellent mechanical properties,light transmission,flame retardancy,gas barrier,bioactivity,biocompatibility and biodegradability.Layered double hydroxides(LDHs)delaminated in a solvent,nanosheets with a large specific surface area and biocompatibility can be obtained,which is an ideal two-dimensional nanomaterial for improving polymer properties.From the perspective of fully utilizing the abundant chitin and cellulose in nature,this thesis sodium hydroxide/urea solvent was used to delaminate LDHs,and dissolve chitin and cellulose.The nanosheet of Mg/AI-LDHs is chose as the reinforcing phase of cellulose and chitin,which mimics the mechanical strengthening mechanism of the nanocrystalline in natural cellulose fibers,in order to improve the mechanical properties of regenerated cellulose and chitin.The main research contents are as follows:MgAl-LDHs(LDHs-hy)were synthesized by urea hydrolysis method.LDHs-hy was successfully exfoliated in NaOH/urea/water solution to obtain a colloidal solution containing LDHs-hy two-dimensional nanosheets.LDHs-hy/chitin nanocomposites(LHCHNF)were prepared by model casting methed affter hot-pressing affer LDHs-hy and chitin being dissolved in the same solvent.The effects of LDHs-hy content on the mechanical properties,thermal stability,gas permeability and light transmittance of chitin film materials were investigated.The results showed that the crystallization degrees of chitin decreases due to the motion of chitin segments is limited by LDHs-hy nanosheets.The degree of crystallization of chitin.When the LDHs-hy content reaches 8%,LDHs-hy restacks in the chitin matrix.With the LDHs-hy content increasing,the tensile modulus and the strength of chitin.Gradually increasing,and the maximum increase in tensile strength is 44.4%.LDHs-hy nanosheets increases the the third thermal decomposition temperature of chitin,and the amount of char formation,and reduces the heat release amount during dehydration and CO2 dislocation.The heat released from the breakage and cross-linking of the main chain reduces.These results imply that LDHs-hy nanosheets can increase the thermal stability of the chitin.When the LDHs-hy content is 4%,the gas permeability coefficient of chitin is lowerest.The barrier gas performance of the LHCHNF is increased.Secondly,the LDHs-hy/cellulose nanocomposite was studied.The LDHs-hy was delaminated into the LiOH H2O/urea/water solution,and the cellulose dissolved in the same solvent.The LDHs-hy/cellulose nanocomposite(LCENF)was prepared by followed by hot pressing.The effects of LDHs-hy content on the mechanical properties,thermal stability and light transmittance of cellulose film materials were investigated.The results show that LDHs-hy can be completely and uniformly dispersed in the cellulose matrix when the content is in the range of 0-8 wt%,and no restacking of the LDHs-hy nanosheets occurs.The mechanical test results show that when the LDHs-hy content in LCENF is 2%,the tensile strength increases from 18.16 MPa to 50.22 MPa,an increase of 176.5%.When the content of LDHs-hy is more than 2%,the tensile strength of LCEEN is gradually reduced from 50.22 MPa to 13.26 MPa.Thermal analysis of LCENF shows that the LDHs-hy nanosheet reduces the rate of the first-step thermal decomposition of cellulose and the on-set temperature of the second-step thermal decomposition.The first-step decomposition temperature of celllose main chain increases,and the heat release from thermal oxidation inhigh temperature is obstructed.It is shown that the LDHs-hy nanosheets significantly increase the thermal stability of cellulose.LCENF is a very light-transmissive film after polishing.It is showed that the transmittance of LCENF with different contents of LDHs-hy was between 1.1 and 2.0 at a wavelength of 600 nm,and LDHs-hy had little effect on the transmittance of LCENF.When the LDHs-hy content reaches 10%by weight,the transmittance of LCENF reaches a maximum of 3.3.The above research results provide a feasible route for the preparation of natural polymer nanocomposites in order to make full use of natural polymers with abundant sources,excellent performance,low cost and environmental protection.It also provides an experimental basis for the performance and practical application of natural polymer matrix-based nanocomposites.It provides a research basis for promoting the development and application of natural polymer materials.更多还原