Daassi Rodrigue, Durand Kalvin, Rodrigue Denis, Stevanovic Tatjana
Renewable Materials Research Centre (CRMR), Institute of Nutrition and Functional Foods (INAF), Université Laval, Quebec City, QC G1V 0A6, Canada.
Chemical Engineering Department, Université Laval, Quebec City, QC G1V 0A6, Canada.
Polymers (Basel). 2023 Jul 7;15(13):2973. doi: 10.3390/polym15132973.
The development of new processing methods is required in order to meet the continuous demand for thinner films with excellent barrier properties for food packaging and other applications. In this study, rice husk organosolv lignin nanoparticles were prepared using the electrospray method, which were applied to produce polylactic acid (PLA)-based films for food packaging. The effect of the following electrospray parameters has been investigated: lignin concentration (LC) ranging from 5-50 mg/mL, flow rate (FR) from 0.5-1 mL/min, applied voltage from 10-30 kV, and tip-to-collector distance (TCD) from 10-25 cm, on the morphology, size, polydispersity index (PDI), and Zeta potential (ZP) of lignin nanoparticles (LNPs). The response surface methodology with a Box-Behnken design was applied to optimize these parameters, while dynamic light scattering (DLS) and scanning electron microscopy (SEM) analyses were used to characterize the controlled LNPs. The results showed that the LNPs shape and sizes represent a balance between the solvent evaporation, LC, applied voltage, TCD and FR. The application of optimal electrospray conditions resulted in the production of LNPs with a spherical shape and a minimal size of 260 ± 10 nm, a PDI of 0.257 ± 0.02, and a ZP of -35.2 ± 4.1 mV. The optimal conditions were achieved at LC = 49.1 mg/mL and FR = 0.5 mL/h under an applied voltage of 25.4 kV and TCD = 22 cm. Then, the optimized LNPs were used to improve the properties of PLA-based films. Three types of PLA-lignin blend films were casted, namely lignin/PLA, LNPs/PLA and PLA-grafted LNPs. PLA-grafted LNPs exhibited a more uniform dispersion in PLA for lignin contents of up to 10% than other composite samples. Increasing the lignin content from 5% to 10% in PLA-grafted LNPs resulted in a significant increase in elongation at break (up to four times higher than neat PLA). The presence of PLA-grafted lignin led to a substantial reduction in optical transmittance in the UV range, dropping from 58.7 ± 3.0% to 1.10 ± 0.01%, while maintaining excellent transparency to visible light compared to blends containing lignin or LNPs. Although the antioxidant capacity of unmodified lignin is well-known, a substantial increase in antioxidant capacity was observed in LNPs and PLA-grafted LNP films, with values exceeding 10 times and 12 times that of neat PLA, respectively. These results confirm the significant potential of using studied films in food packaging applications.
为了满足对用于食品包装和其他应用的具有优异阻隔性能的更薄膜的持续需求，需要开发新的加工方法。在本研究中，采用电喷雾法制备了稻壳有机溶剂木质素纳米颗粒，并将其应用于生产用于食品包装的聚乳酸（PLA）基薄膜。研究了以下电喷雾参数的影响：木质素浓度（LC）范围为5 - 50 mg/mL、流速（FR）为0.5 - 1 mL/min、施加电压为10 - 30 kV以及针尖到收集器的距离（TCD）为10 - 25 cm，对木质素纳米颗粒（LNPs）的形态、尺寸、多分散指数（PDI）和zeta电位（ZP）的影响。采用Box-Behnken设计的响应面方法对这些参数进行优化，同时使用动态光散射（DLS）和扫描电子显微镜（SEM）分析来表征可控的LNPs。结果表明，LNPs的形状和尺寸代表了溶剂蒸发、LC、施加电压、TCD和FR之间的平衡。应用最佳电喷雾条件可生产出球形且最小尺寸为260±10 nm、PDI为0.257±0.02且ZP为 - 35.2±4.1 mV的LNPs。在25.4 kV的施加电压和TCD = 22 cm条件下，当LC = 49.1 mg/mL和FR = 0.5 mL/h时达到最佳条件。然后，将优化后的LNPs用于改善PLA基薄膜的性能。浇铸了三种类型的PLA-木质素共混薄膜，即木质素/PLA、LNPs/PLA和PLA接枝LNPs。对于高达10%的木质素含量，PLA接枝LNPs在PLA中表现出比其他复合样品更均匀的分散性。在PLA接枝LNPs中，将木质素含量从5%增加到10%导致断裂伸长率显著增加（比纯PLA高四倍）。PLA接枝木质素的存在导致紫外范围内的透光率大幅降低，从58.7±3.0%降至1.10±0.01%，同时与含有木质素或LNPs的共混物相比，对可见光保持优异的透明度。尽管未改性木质素的抗氧化能力是众所周知的，但在LNPs和PLA接枝LNP薄膜中观察到抗氧化能力大幅增加，其值分别超过纯PLA的10倍和12倍。这些结果证实了所研究的薄膜在食品包装应用中的巨大潜力。
