【摘要】：纖維素微纖絲(CMF)由于其強(qiáng)度高、重量輕、可再生的特點(diǎn),以及其表現(xiàn)出的良好的生物相容性、可降解性和阻隔性能而備受關(guān)注。由于機(jī)械解離制備CMF所需能耗過高,并且產(chǎn)品尺寸分布不均勻,因此CMF很難實(shí)現(xiàn)產(chǎn)業(yè)化。生物酶預(yù)處理是解決該問題的一個(gè)有效方法,先對(duì)纖維原料進(jìn)行預(yù)處理,降低微纖絲之間的結(jié)合力,使其易于微纖化,然后再進(jìn)行機(jī)械解離,可以大幅降低機(jī)械能耗。本課題重點(diǎn)研究酶預(yù)處理對(duì)細(xì)胞壁結(jié)構(gòu)的影響以及酶預(yù)處理對(duì)機(jī)械解離制備CMF的促進(jìn)作用。通過控制漂白馬尾松纖維的酶預(yù)處理程度的方式來改變纖維細(xì)胞壁的結(jié)構(gòu),然后進(jìn)行不同程度的高壓均質(zhì)處理,以此來探究纖維細(xì)胞壁結(jié)構(gòu)對(duì)于機(jī)械解離的影響,從而揭示酶預(yù)處理促進(jìn)機(jī)械解離制備CMF的機(jī)理。在酶水解過程中,纖維細(xì)胞壁發(fā)生切斷、撕裂、剝皮、潤脹和侵蝕。漂白馬尾松纖維表面存在大量紋孔呈線性排列,撕裂作用主要發(fā)生在紋孔所在區(qū)域。斷頭率和扭結(jié)纖維含量的變化反映了纖維被切斷的程度。漂白馬尾松纖維經(jīng)5.0FPU/g纖維素酶降解2h后,纖維被切斷次數(shù)達(dá)到最大,約為3~4次。隨酶用量的增加,細(xì)胞壁比表面積呈現(xiàn)先減小后增加再減小再增加的“W型”變化,纖維素結(jié)晶度的變化趨勢恰好與之相反,呈現(xiàn)先增加后減小再增加再減小的“M型”變化;纖維素酶經(jīng)細(xì)胞壁的中孔和大孔進(jìn)入細(xì)胞壁結(jié)構(gòu)內(nèi)部,隨著酶用量的增加,中孔總體積先增加然后保持穩(wěn)定,大孔總體積先增加后減少,微孔總體積稍有減小,總孔體積的變化趨勢與大孔總體積的變化趨勢相同。微纖化主要局限于細(xì)胞壁的表面,沿細(xì)胞壁本身向邊緣蔓延,最終細(xì)胞壁被完全解離,進(jìn)而得到CMF。酶預(yù)處理破壞纖維細(xì)胞壁結(jié)構(gòu),提高比表面積,使得微纖化區(qū)域增加,促進(jìn)細(xì)胞壁的解離。高壓均質(zhì)處理程度越高,纖維的微纖化程度越高,相應(yīng)的機(jī)械能耗也越高。隨著均質(zhì)次數(shù)的增加,纖維粒徑、纖維素平均聚合度呈下降趨勢,纖維保水值和熱穩(wěn)定性以及CMF薄膜透光率呈上升趨勢。高壓均質(zhì)機(jī)的能耗主要取決于物料體積和均質(zhì)次數(shù),固含量對(duì)其影響較小。纖維素酶預(yù)處理破壞了纖維細(xì)胞壁的基本結(jié)構(gòu),形成具有較大比表面積的纖維碎片和片段,增加了微纖化發(fā)生的區(qū)域。分別以CMF直徑分布、能量消耗、纖維素平均聚合度和CMF薄膜透光率為指標(biāo),評(píng)價(jià)酶預(yù)處理對(duì)機(jī)械解離制備CMF的促進(jìn)作用。結(jié)果表明,漂白馬尾松纖維在100MPa壓力下均質(zhì)處理30次后得到的MFC的聚合度為354,直徑主要分布在20~50nm;漂白馬尾松纖維在50℃下經(jīng)10.0FPU/g纖維素酶水解2h,在100MPa壓力下均質(zhì)處理30次后得到的MFC的聚合度為229,直徑主要分布在10~40nm。相同均質(zhì)條件下,解離酶預(yù)處理纖維較解離原料纖維而言,能量消耗更少,且解離效果更好。
[Abstract]:Cellulose microfibrillar (CMF) has attracted much attention due to its high strength, light weight, reproducibility, and its good biocompatibility, degradability and barrier properties. Because the energy consumption of mechanical dissociation to prepare CMF is too high and the product size distribution is not uniform, it is difficult to realize the industrialization of CMF. Biological enzyme pretreatment is an effective method to solve this problem. Firstly, pretreatment of fiber raw materials to reduce the adhesion between microfibrils, make it easy to micro-fibrillate, then mechanical dissociation, can greatly reduce the mechanical energy consumption. The effect of enzyme pretreatment on cell wall structure and the effect of enzyme pretreatment on the preparation of CMF by mechanical dissociation were studied. By controlling the degree of enzyme pretreatment of bleached Masson pine fiber, the structure of cell wall was changed, and then treated with different degrees of high pressure homogenization, so as to explore the effect of cell wall structure on mechanical dissociation. Therefore, the mechanism of enzyme pretreatment promoting mechanical dissociation to prepare CMF was revealed. During enzymatic hydrolysis, the cell wall is cut, torn, peeled, swelled and eroded. A large number of holes on the surface of bleached Masson pine fiber were linearly arranged, and the tearing action mainly occurred in the region where the holes were located. The change of breakage rate and kink fiber content reflects the degree of fiber being cut off. When the bleached Masson pine fiber was degraded by 5.0FPU/g cellulase for 2 hours, the number of cut off reached the maximum, about 34 times. With the increase of enzyme dosage, the specific surface area of cell wall showed a change of "W type" which decreased first, then increased then decreased, and then increased. The change trend of cellulose crystallinity was just the opposite, showing the change of "M type" which increased first and then decreased. Cellulase entered the cell wall structure through the mesopore and macropore of the cell wall. With the increase of the amount of enzyme, the total volume of the mesopore first increased and then remained stable, the total volume of the macropore increased first and then decreased, and the total volume of the micropore decreased slightly. The change trend of total pore volume is the same as that of large pore volume. Microfibrillarization is mainly confined to the surface of the cell wall, spreading along the cell wall itself to the edge. Finally, the cell wall is completely dissociated and CMF. is obtained. Enzyme pretreatment destroyed the cell wall structure, increased the specific surface area, increased the microfibrillarization area, and promoted the dissociation of the cell wall. The higher the treatment degree of high pressure homogenization, the higher the degree of fiber microfibrillation and the higher the corresponding mechanical energy consumption. With the increase of homogenization times, the particle size and average polymerization degree of cellulose decreased, the water retention value and thermal stability of fiber and the transmittance of CMF film increased. The energy consumption of high pressure homogenizer mainly depends on the volume of material and the times of homogenization, and the content of solid has little effect on it. The cellulase pretreatment destroyed the basic structure of the cell wall, formed fiber fragments and fragments with large specific surface area, and increased the area of microfibrillation. Based on the diameter distribution of CMF, energy consumption, average polymerization degree of cellulose and transmittance of CMF film, the effect of enzyme pretreatment on the preparation of CMF by mechanical dissociation was evaluated. The results showed that the degree of polymerization of bleached Masson pine fiber after 30 times homogenization treatment under 100MPa pressure was 354, and the diameter of MFC was mainly distributed at 20 ~ 50nm. Bleached Masson pine fiber was hydrolyzed by 10.0FPU/g cellulase at 50 鈩，

本文編號(hào)：2352356