In this study, cellulose nanofibrils (CNFs) were modified by catalyzed lactic acid esterification in an aqueous medium with SnCl₂ as a catalyst. Films were made from unmodified and lactic acid-modified CNF without a polymer matrix to evaluate the effectiveness of the modification. Ungrafted and lactic acid-grafted CNF was also compounded with poly(lactic acid) (PLA) to produce composites. Mechanical, water absorption, and barrier properties were evaluated for ungrafted CNF, lactic acid-grafted CNF films, and PLA/CNF composites to ascertain the effect of lactic acid modification on the properties of the films and nanocomposites. FTIR spectra of the modified CNF revealed the presence of carbonyl peaks at 1720 cm⁻¹, suggesting that the esterification reaction was successful. Modification of CNF with LA improved the tensile modulus of the produced films but the tensile strength and elongation decreased. Additionally, films made from modified CNF had lower water absorption, as well as water vapor and oxygen permeability, relative to their counterparts with unmodified CNFs. The mechanical properties of PLA/CNF composites made from lactic acid-grafted CNFs did not significantly change with respect to the ungrafted CNF. However, the addition of lactic acid-grafted CNF to PLA improved the water vapor permeability relative to composites containing ungrafted CNF. Therefore, the esterification of CNFs in an aqueous medium may provide an environmentally benign way of modifying the surface chemistry of CNFs to improve the barrier properties of CNF films and PLA/CNF composites.

中文翻译：

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纤维素纳米纤丝的乳酸表面改性对纤维素纳米纤丝薄膜和纤维素纳米纤丝-聚乳酸复合材料性能的影响

_{在这项研究中，纤维素纳米纤丝 (CNF) 通过在 SnCl 2}作为催化剂的水性介质中催化乳酸酯化进行改性。薄膜由未改性和乳酸改性的 CNF 制成，没有聚合物基质，以评估改性的有效性。未接枝和乳酸接枝的 CNF 还与聚乳酸 (PLA) 复合以生产复合材料。对未接枝的 CNF、乳酸接枝的 CNF 薄膜和 PLA/CNF 复合材料的机械性能、吸水性和阻隔性能进行了评估，以确定乳酸改性对薄膜和纳米复合材料性能的影响。改性 CNF 的 FTIR 光谱显示在 1720 cm ^{-1处存在羰基峰}, 表明酯化反应是成功的。用 LA 改性 CNF 提高了所生产薄膜的拉伸模量，但拉伸强度和伸长率下降。此外，与未改性 CNF 的对应物相比，由改性 CNF 制成的薄膜具有较低的吸水率以及水蒸气和氧气渗透性。由乳酸接枝的 CNF 制成的 PLA/CNF 复合材料的机械性能相对于未接枝的 CNF 没有显着变化。然而，相对于含有未接枝 CNF 的复合材料，将乳酸接枝 CNF 添加到 PLA 中提高了水蒸汽渗透性。所以，