【作者】 吴燕；

【导师】 周定国； 王思群； 张洋；

【作者基本信息】 南京林业大学 ， 木材科学与技术， 2009， 博士

【摘要】 本论文以十种阔叶材和五种农作物秸秆纤维为研究对象,通过纳米压痕实验和原子力显微镜（AFM）等手段研究了纤维细胞壁的力学性能。并以其中的稻秸纤维素纤维为原料,利用高能超声波法和高压纳米均质机法分别制备了微/纳米纤丝,探讨了分别以聚丙烯（PP）和聚乙烯醇（PVA）为基体物质、以微/纳米纤丝为增强材料,制取微/纳米纤丝/PP和微纳米纤丝/PVA纳米复合材料的合成方法、工艺条件、改性剂以及微/纳米纤丝含量对纳米复合材料力学性能、热学性能和纳米复合材料界面特性的影响。本研究得到的结论归纳如下:1) SilviScan系统所测得的弹性模量中,摘亚木的值最大,为35.4GPa;杨木的值最小,为14.2GPa。其中,木材密度对于弹性模量的大小,起到了关键性的作用。较高的密度对应于较高的弹性模量。并且随着木材密度的增大,弹性模量增大;而随着MFA的增加而减小。纳米压痕实验所测得的细胞壁弹性模量最大值出现在摘亚木木材样品,其数值为24.6GPa,这个数值低于由SilviScan测试系统所测得的数值（35.4GPa）;细胞壁弹性模量的最低值同样出现在杨木木材样品中,其数值为16.9GPa。最小值与最大值相差的百分比为31.3%。细胞壁弹性模量随木材密度的增加而增大,随MFA的增大而减小。九个木材样品细胞壁硬度的数值在0.44-0.56 GPa范围。细胞壁的硬度与微纤丝角没有明显的相关性。2)麦秸纤维细胞壁的弹性模量值最大,为20.8GPa,豆秆和棉秆的值最小,为16.3GPa。五种农作物秸秆纤维细胞壁弹性模量的平均值为18.4GPa。五种农作物秸秆纤维细胞壁的弹性模量介于阔叶材和针叶材之间。棉秆纤维细胞壁的硬度值最大,为0.85GPa。豆秆纤维细胞壁的硬度值最小,为0.48GPa。麦秸纤维的细胞壁弹性模量和硬度高于稻秸纤维。农作物秸秆纤维细胞壁的硬度大于木材树种和再生纤维素纤维。在纳米尺度下,农作物秸秆纤维具有相对优于木材树种和再生纤维素纤维的纳米力学性能。3)经高能超声波处理后的稻秸纤维素纤维微纳米纤丝的粒径分布范围在0.1～80μm之间。直径小于500nm的纤丝占总体测试样品的6.3%;90%的微/纳米纤丝的粒径分布在7.0～80μm范围;测试样品平均粒径为41μm。经高压纳米均质机处理得到的稻秸纤维微/纳米纤丝的粒径分布范围在0.1～25μm。直径小于500nm的纤丝占总体测试样品的16%;90%的微/纳米纤丝的粒径分布在0.7～25μm范围;测试样品平均粒径为8.8μm。未处理的稻秸纤维素纤维、高能超声波法制备的稻秸纤维素纤维微/纳米纤丝和高压纳米均质机法制备的稻秸纤维素纤维微/纳米纤丝的相对结晶度分别为71.3%、72.9%和68.0%。与未处理的稻秸纤维素纤维相比,经高能超声波法和高压纳米均质机法处理得到的稻秸微/纳米纤丝的-OH特征吸收峰均向高波数移动。电子扫描电镜（SEM）的研究结果表明:经高能超声波和高压纳米均质机处理后的纤维细胞壁破碎,产生分层剥落现象,还有一些细小纤丝从纤维束中分离出来,发生一定的纤丝化作用。4)在不同的挤出合成条件下,纳米复合材料的弹性模量提高,材料的刚性增加,而拉伸强度均低于未添加增强材料的聚丙烯的强度,拉伸断裂伸长率显著降低;微/纳米纤丝的含量从2%增加到11%时,纳米复合材料的拉伸强度在微/纳米纤丝含量达到5%时出现最大值,为31.7MPa,而弹性模量在微/纳米纤丝含量达到8%时出现最大值,为1621MPa,拉伸断裂伸长率随着微/纳米纤丝的含量增加显著降低;MAPP的不同含量对材料的拉伸强度和拉伸断裂伸长率没有明显的影响,在MAPP含量为4%时,纳米复合材料的弹性模量达最大值1509MPa;在高能超声波的不同处理条件的研究中发现,随着处理时间的延长,合成所得纳米复合材料的拉伸强度、弹性模量和拉伸断裂伸长率均提高,且处理浓度为1%的各项指标均高于处理浓度为0.5%的样品性能。当PP基体中引入了改性剂MAPP和RSF时,基体的红外光谱图有很大的变化。1224CM^-1,1074 CM^-1和1028 CM^-1的酯基（C-O-C）伸缩振动吸收峰的出现,证明MAPP的加入使PP基体与RSF具有很好的相容性。SEM的研究结果表明:微纳米纤丝被包裹在PP/MAPP基体中,在拉伸实验过程中,没有从基体中被拔出,展示了很好的相容性。5)自然条件和-20℃冷冻-解冻循环三次条件下所得微纳米纤丝/聚乙烯醇纳米复合材料的拉伸强度均高于纯PVA薄膜的拉伸强度。并且,在-20℃冷冻-解冻循环三次条件下所得的纳米复合材料的拉伸强度均高于相应组分在自然条件下铸膜所得的样品。6)在自然条件下铸膜所得的微纳米纤丝/聚乙烯醇纳米复合材料在25～150℃范围内的储能模量（E′）当微纳/米纤丝的含量为2%和11%时低于纯PVA的E′;在-20℃冷冻-解冻循环三次条件下铸膜制备的微纳米纤丝/聚乙烯醇纳米复合材料在60℃以下高于纯PVA的E′,在60℃以上几乎没有明显变化。复合材料的tanδ与纯PVA凝胶薄膜的tanδ相比,在整个温度范围内没有明显的差别,而T_g温度均高于纯PVA凝胶薄膜。而自然条件和-20℃冷冻-解冻循环三次条件下铸膜,微纳米纤丝不同含量的纳米复合材料的熔点没有太大的变化。-20℃冷冻-解冻循环三次条件下所得微纳米纤丝/聚乙烯醇纳米复合材料的结晶度要高于自然条件下铸膜所得微纳米纤丝/聚乙烯醇纳米复合材料的结晶度。稻秸纤维素纤维微/纳米纤丝的加入,提高了材料的热稳定性。并且-20℃冷冻-解冻循环三次条件下铸膜制备的各种组分样品的最大失重率温度（T_p）均高于自然条件铸膜的样品,并且随着微/纳米纤丝含量的增加T_p有不同程度的提高。微纳米纤丝/聚乙烯醇纳米复合材料的红外光谱中保留了微/纳米纤丝和PVA的一些特征吸收峰,同时,由于两者在共混过程中发生了化学作用,图谱上由-OH振动引起的特征吸收峰的位置发生变化,说明微/纳米纤丝与PVA具有很好的相容性。更多还原

【Abstract】 This study investigated the nano-mechanical properties of fiber cell walls of ten hardwoods and five crop stalks by nanoindentation and atomic force microscopy（AFM）.And also the rice straw cellulose fiber was used to produce rice straw micro/nano fibrils（RSF） by high intensity ultrasonication（HIUS） and high pressure homogenizer（HPH）.The fibrils were used to reinforce polypropylene（PP） and poly（vinyl alcohol） by compression molding and film casting. The effects of the compounding methods,technical conditions,compatilizer addition and fibril loadings on tensile properties,dynamic mechanical and thermal properties of resultant nanocomposites were investigated.The conclusions were listed as following:The SilviScan elastic modulus of Keranji appeared to exhibit the highest value of 35.4 GPa, whereas poplar exhibited the lowest elastic modulus of 14.2 GPa.Moreover the scanned wood density is the predominant factor that determines the SilviScan elastic modulus.The higher the scanned wood density,the higher is the SilviScan elastic modulus.The SilviScan elastic modulus increased with wood density and decreased with microfibril angle（MFA）.The highest cell-wall elastic modulus of 24.6 GPa was observed in Keranji,which was lower than its SilviScan modulus（35.4 GPa）.The lowest elastic modulus of 16.9 GPa was observed in Poplar. The percentage of the difference in elastic modulus between Keranji and Poplar was 31.3%. The wood cell-wall elastic modulus increased with wood density and decreased with MFA.The values of hardness of cell wall varied from 0.44 to 0.56 g/cm³.It appeared that there was no obvious relationship between cell-wall hardness and MFA.Wheat straw has the highest elastic modulus of 20.8 GPa within five crops.The soybean stalk and cotton stalk both exhibit the lowest values of 16.3 GPa among the five crop stalks.The mean value of five crop stalks was 18.4 GPa.The values of the elastic moduli of cell walls of crop stalks（16.3-20.8 GPa） were comparable to that of most of hardwood species（16.9-24.6 GPa） and was higher than that of some softwoods（15.0-18.0 GPa） and lyocell fiber（11.5-13.2 GPa）.The cotton stalk cell walls showed the highest hardness of 0.85 GPa.The lowest hardness of 0.48 GPa was observed in soybean stalks.The percentage of difference in hardness was up to 43.5%among five crops.The mean value of hardness in crop stalks was the highest one（0.60 GPa） compared with the lower value of 0.39 GPa in lyocell fiber and 0.49 GPa in hardwoods and 0.41 GPa in softwoods.This indicates that crops stalk fibers have relatively better nano-mechanical properties than wood and lyocell fiber. The distribution of diameters of RSF ranged from 0.1μm to 80μm by HIUS treatment.The percentage was 6.3%of RSF which diameters were less than 500 nm;almost 90 percents of RSF distributed between 7.0μm and 80μm;the average diameter was 41μm.The distribution of diameters of RSF ranged from 0.1μm to 25μm by HPH treatment.The percentage was 16% of RSF which diameters were less than 500 nm;almost 90 percents of RSF distributed between 0.7μm and 25μm;the average diameter was 8.8μm.The relative crystallinities of untreated rice straw cellulose fibers and rice straw cellulose fibers treated by HIUS and HPH were 71.3%, 72.9%and 68.0%,respectively.The FTIR spectra showed that the -OH peaks moved to higher wavenumbers in rice straw cellulose fibers treated by HIUS and HPH than untreated fibers.The SEM images showed:the fiber cell walls were crashed by HIUS and HPH treatments,and the fibers appeared the phenomena of layered and fibrillation.The fibrils were isolated from the fiber aggregations.The elastic modulus increased of RSF/PP nanocomposite comparing with PP/MAPP polymer. However,the tensile strength and elongation at break of 5%rice straw fibril reinforcing PP nanocomposite was lower than PP/MAPP polymer at different extruder compounding conditions.The tensile strength at 5%RSF loading was up to the maximum value,31.7 MPa, which was a little higher than the value of PP/MAPP polymer,30.83 MPa.The maximum was 1621 MPa at the 8%RSF,which was 17%higher than the value of PP/MAPP polymer.The elongation at break showed a significant decreasing trend with increasing the fibril loading. There was no distinct influence of tensile strength and elongation of nanocomposite and PP/MAPP polymer with increasing MAPP content.The maximum of elastic modulus was 1509 MPa at the 4%of MAPP.The tensile properties increased distinctly with increasing ultrasonication treat time.The tensile strength of 0.5%rice straw cellulose fiber content was lower than 1%rice straw cellulose fiber content at different ultrasonication treat time.After adding MAPP and RSF into PP matrix,the FTIR spectra had big changes.The absorption peak of ester bonds（C-O-C） appeared at 1224 CM^-1,1074 CM^-1 and 1028 CM^-1,which proved that there had been a good compatibility between PP matrix and RSF.The SEM images showed:the fibrils were embedded into the PP/MAPP matrix,during the tensile test,which were not pulled out from the matrix.The tensile strength of the nanocomposites was higher than PVA matrix.Moreover,the tensile strength of the nanocomposites casting at -20℃freezing and thawing 3 cycles condition were higher than the nanocomposites casting at room temperature.When casting at room temperature,the storage flexural modulus（E’） of the nanocomposites higher than PVA by adding 2%～11%RSF into the PVA matrix.When casing at -20℃freezing and thawing three 3 cycles condition,the E’ of nanocomposites were higher than PVA matrix at up 60℃condition;and there was no distinct discrepancy at under 60℃condition.When comparing of the damping factor（tanδ） of RSF/PVA nanocomposites and PVA matrix,which had no clear difference at whole temperature range.However,the glass transition temperatures （T_g） were higher than the PVA matrix.There were no big changes of melt temperature of nanocomposites casting at room temperature and -20℃freezing and thawing three 3 cycles conditions.The crystallinity（X_C） of nanocomposites casting at -20℃freezing and thawing three 3 cycles condition was higher than the nanocomposites casting at room temperature.The adding of fibrils improved the thermo stability of PVA matrix.The maximum ratio of weightlessness（T_p） of nanocomposites casting at -20℃freezing and thawing three 3 cycles condition was higher than the nanocomposites casting at room temperature,and T_p increased with fibrils loadings.The FTIR spectra of RSF/PVA nanocomposites contained the characters of PVA matrix,however,because of the chemical reactions during blending,the peak of-OH changed,which proved a good compatibility between RSF and PVA matrix.更多还原