Influence of Fine Structure on the Variations of Thermal and Mechanical Properties in Flax Fibers Modified with Different Alkaline Treatment Conditions

ABSTRACT

The alkaline treatment condition plays a crucial role in governing the ultimate properties of flax fibers. In this study, flax fibers were modified with mild alkalization and severe mercerization conditions to give fundamental insight into how the molecular-scale changes in cell wall fine structure and cellulose supramolecular structure can affect the macroscopic properties of fibers. SEM, FTIR, XRD, TGA, and DSC techniques were employed to characterize the variations in morphology, composition, crystalline structure, and thermal properties of fibers. Also, tensile tests evaluated their reinforcing performance in polypropylene-based composites. The results indicated that alkalization in 5% (w/v) NaOH solution preserved the tensile properties of fibers, shifted their thermal decomposition temperature from 198 to 254°C, and effectively decreased their moisture absorption content by 18%. The improvements primarily originate from the partial removal of noncellulosic constituents and promoted crystallinity of native cellulose I_β structure. However, mercerization in 20% (w/v) solution significantly reduced the rigidity of fibers in the longitudinal direction. Furthermore, it decreased the moisture absorption only by 6% and shifted the thermal degradation to 275°C. The excessive elimination of noncellulosic constituents and the polymorphic transformation, which led to a weaker hydrogen bonding network in the cellulose II region, accounts for these changes.

摘要

碱处理条件对亚麻纤维的最终性能起着至关重要的作用. 本研究通过对亚麻纤维进行轻度碱化和重度丝光改性，初步探讨了细胞壁精细结构和纤维素超分子结构的分子尺度变化对纤维宏观性能的影响. 采用SEM、FTIR、XRD、TGA和DSC等技术对纤维的形貌、组成、晶体结构和热性能进行了表征. 同时，通过拉伸试验评价了它们在聚丙烯基复合材料中的增强性能. 结果表明，在5%（w/v）NaOH溶液中碱化处理能保持纤维的拉伸性能，使纤维的热分解温度由198℃提高到254℃，有效地降低了纤维的吸湿率18%. 这些改进主要源于部分去除非纤维素成分和提高天然纤维素Iβ结构的结晶度. 然而，在20%（w/v）溶液中丝光显著降低了纤维的纵向刚性. 此外，它只降低了6%的吸湿性，并将热降解转移到275℃. 非纤维素组分的过度消除和多态性转化导致纤维素ll区氢键网络的减弱，是这些变化的原因.

KEYWORDS:

• Surface modification
• peak deconvolution
• hydrogen bonding
• Rietveld refinement
• crystallinity index
• natural composite

关键词:

• 表面改性
• 峰值反褶积
• 氢键
• 精炼
• 结晶指数
• 天然复合材料

Acknowledgments

The authors wish to express their gratitude to Prof Gholamreza Pircheraghi, Ms. Tanin Fazel, and Mr. Amirmehdi Salehi for their kind comments, support, and guidance. The authors gratefully acknowledge financial support from Parsa Polymer Sharif Company.

Influence of fine structure on the variations of thermal and mechanical properties in flax fibers modified with different alkaline treatment conditions

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