打浆压溃作用对切短纤维形态结构的影响

【目的】基于植物细胞壁微观结构特征,建立纤维S₂层微纤丝长度与微纤角的关系模型,并计算出适合制备纳米纤维的纤维长度。【方法】利用打浆机疏解将纤维快速切短至计算长度范围,在pH 7.5的碱性环境下对切短后纤维进行压溃处理,观察纤维形态结构的变化。【结果】平均长度在0.41～0.64 mm范围内的切短纤维经压溃处理后,纤维刚性结构遭到破坏,产生纵向开裂,水合Na⁺从纤维端面及表面裂纹处渗透进入纤维内部并产生润胀水化,纤维保水值由125.6%增大至319.3%,有效地破除了纤维细胞壁的P层和S₁层,由此削弱了纤维微纤丝层间结合力。纤维结晶度及热重分析表明,纤维压溃初期(保水值125.6%),其结晶度为72%～73%,热解活化能为75.02～76.93 kJ/mol; 随着压溃强度的增加(保水值319.3%),纤维结晶度降低至45%,热解活化能降低至37.78 kJ/mol,进一步说明了纤维经一定强度的压溃处理可有效削弱纤维微纤丝层间结合力。【结论】针对不同类型纤维原料及纤维形态结构,应将纤维切短至合适长度,可使纤维更易被压溃、吸水润胀及微纤丝化。

Effects of the beating and crushing action on the morphological structure of cut-fiber

【Objective】The model of the relationship between microfibril length and microfibril angle in S₂ fiber layer was developed based on the microstructure characteristics of plant cell walls, which can be used to estimate the fiber length for the preparation of nanofibers. 【Method】The fibers were cut to the range of the calculated length quickly by the free beating and crushing by the subsequent alkaline treatment(pH = 7.5). The morphology and structure changes were examined using a combination of AFM and TEM. 【Result】The water retention value(r(WRV))increased drastically from 125.6% to 319.3% for the fibers that had a length ranging from 0.41-0.64 mm. The rigid structure of fibers was easily destroyed due to the generating of longitudinal cracking. The results also demonstrated that it would be much easier for Na⁺ ion to penetrate the internal layers of fibers from fiber ends and surface cracks, resulting in swelling fibers, removing P and S₁ layers of the fibers’walls, and decreasing fibers’bonding effectively. From the characterization results, the crystallinity of the fibers was 72%-73% and the activation energy of pyrolysis was 75.02-76.93 kJ/mol in the early stage of compression(r(WRV)=125.6%). With the increase of the compressive strength(r(WRV)=319.3%), the crystallinity of the fibers decreased to 45% and the activation energy of pyrolysis decreased to 37.78 kJ/mol. This further confirmed that the fiber with a certain strength crushing treatment can effectively weaken the binding force between the fiber microfibril layers. 【Conclusion】The fibers originated from different types of raw materials and possessed different morphologies can be cut into short fibers with an appropriate length, thus facilitating the crush, swell and micro-miniaturized process.