Fluorescent labeling and image analysis of cellulosic fillers in biocomposites: Effect of added compatibilizer and correlation with physical properties

The performance of cellulosic filler/polyolefin biocomposites is affected by the filler dispersion (aggregation and spatial arrangement) in the matrix. However, this mechanistic factor is generally inferred from the physical properties of the final bulk material because of the limitations of analytical techniques. Herein, we propose a simple method to quantitatively evaluate the dispersion of filler particles. To accomplish this, the cellulose component in injection-molded specimens of microcrystalline cellulose (MCC)/maleic anhydride-modified polypropylene (MAPP)/polypropylene (PP) composites was selectively fluorescently labeled with calcofluor white, and the dispersion state of tens of thousands of MCC particles observed by fluorescence microscopy was analyzed. The close-range aggregation behavior of the MCC particles can be evaluated by the area of the fluorescent particles (A), and the normality (randomness) of the spatial arrangement can be classified by the skewness of the distribution of the distances between the centroids of the particles (s). As a result, with an increase in the degree of acid modification of the added MAPP, aggregation of MCC was suppressed and the spatial arrangement became random. Both A and s were not associated with the modulus or fracture strain of the injection-molded specimens, but they were correlated with the tensile and bending strengths and water absorption behavior. This visualization method was also applied to a composite containing nanofibrillated cellulose filler (citric acid-modified cellulose nanofiber).

纤维素填料/聚烯烃生物复合材料的性能受基质中填料的分散情况（聚集和空间排列）影响。然而，由于分析技术的局限性，这一机理因素通常是从最终块状材料的物理性质推断出来的。在此，我们提出一种简单的方法来定量评估填料颗粒的分散情况。为此，用荧光增白剂对微晶纤维素（MCC）/马来酸酐改性聚丙烯（MAPP）/聚丙烯（PP）复合材料注塑试样中的纤维素成分进行选择性荧光标记，并对通过荧光显微镜观察到的数以万计的MCC颗粒的分散状态进行分析。MCC颗粒的近距离聚集行为可通过荧光颗粒的面积（A）来评估，空间排列的正态性（随机性）可通过颗粒质心之间距离分布的偏度（s）来分类。结果表明，随着添加的MAPP酸改性程度的增加，MCC的聚集受到抑制，空间排列变得随机。A和s都与注塑试样的模量或断裂应变无关，但它们与拉伸强度、弯曲强度和吸水行为相关。这种可视化方法也应用于一种含有纳米原纤化纤维素填料（柠檬酸改性纤维素纳米纤维）的复合材料。