Effect of the Micronization of Pulp Fibers on the Properties of Green Composites

Abstract

Green composites, composed of bio-based matrices and natural fibers, are a sustainable alternative for composites based on conventional thermoplastics and glass fibers. In this work, micronized bleached Eucalyptus kraft pulp (BEKP) fibers were used as reinforcement in biopolymeric matrices, namely poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB). The influence of the load and aspect ratio of the mechanically treated microfibers on the morphology, water uptake, melt flowability, and mechanical and thermal properties of the green composites were investigated. Increasing fiber loads raised the tensile and flexural moduli as well as the tensile strength of the composites, while decreasing their elongation at the break and melt flow rate. The reduced aspect ratio of the micronized fibers (in the range from 11.0 to 28.9) improved their embedment in the matrices, particularly for PHB, leading to superior mechanical performance and lower water uptake when compared with the composites with non-micronized pulp fibers. The overall results show that micronization is a simple and sustainable alternative for conventional chemical treatments in the manufacturing of entirely bio-based composites.

Natural Polymers-Based Materials: A Contribution to a Greener Future

“…Engineering natural polymers-based materials derived from polysaccharides and proteins is the main objective of the work carried out by the BioPol4fun research group. In the last decade, we have been intensively exploiting cellulose [ 63 , 64 ], nanocelluloses (e.g., bacterial nanocellulose (BNC) [ 61 , 65 , 66 ], nanofibrillated cellulose (CNFs) [ 67 , 68 ] and cellulose nanocrystals (CNCs) [ 69 ]), chitosan [ 70 , 71 , 72 , 73 ], pullulan [ 71 , 74 , 75 , 76 ], starch [ 68 ], hyaluronic acid [ 77 , 78 ], alginate [ 79 ], fucoidan [ 80 , 81 ], agar [ 82 ], lysozyme [ 83 , 84 , 85 , 86 ], and gelatin [ 87 ] ( Figure 1 ) to fabricate films [ 85 , 88 , 89 , 90 , 91 ], membranes [ 81 , 92 , 93 , 94 , 95 ], (nano)composites reference [ 64 , 96 , 97 , 98 , 99 ], coatings [ 100 , 101 , 102 , 103 ], nanosystems [ …”

“…Cellulose is considered the most abundant biopolymer on the planet, being a constituent of most green plants and algae, and naturally secreted in its pure form by some strains of non-pathogenic bacteria (e.g., Komagataeibacter ) [ 66 , 110 ]. This polysaccharide is an eminent feedstock for materials development and can be employed in its native state [ 63 , 64 ] as cellulose derivatives, or in the form of nanofibrils (CNFs) reference [ 85 , 86 , 88 , 89 , 98 , 100 , 101 , 111 ], nanorods (CNCs) [ 69 ], or three-dimensional hydrogel pellicles (BNC) [ 77 , 78 , 79 , 81 , 92 , 93 , 94 , 95 , 104 , 105 , 106 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 ] to manufacture a wide range of materials, as shown in Table 1 . Therefore, the vast majority of the works of our research group entails cellulose nanoforms, i.e., cellulose with at least one dimension in the nanoscale, for the development of nanocomposites [ 98 , ...…”

“…Depending on the substrate, the type of material, and the intended function, several manufacturing strategies are accessible for the development of composites and other cellulosic materials. By taking advantage of thermoplastic matrices, e.g., poly(lactic acid) (PLA), poly(hydroxybutyrates) (PHB), and poly(ε-caprolactone) (PCL), biobased composites reinforced with micronized cellulose fibers [ 64 ], BNC nanofibers, [ 112 , 113 ] and latex-modified CNFs [ 98 ] can be prepared through melt-mixing or hot-pressing approaches. As BNC can be obtained in the form of pellicles with the desired shape, the formulation of functional membranes [ 81 , 95 ] and patches [ 78 , 128 ] is facilitated by the simple diffusion of aqueous solutions of the required (bio)molecules (e.g., drugs [ 77 , 104 , 105 , 126 , 127 , 128 ], polyelectrolytes [ 81 , 95 ], or other natural polymers [ 78 , 81 , 124 ]) into its three-dimensional porous network.…”

“…Owing to their excellent mechanical properties and good thermal stability, cellulose (nano) fibers have been employed as green reinforcing agents for the design of sustainable composites with PLA [ 64 , 112 ], PCL [ 98 , 113 ], and PHB [ 64 ] matrices ( Figure 2 A–C). An interesting issue is that the inclusion of cellulosic fibers, apart from enhancing the mechanical performance of the thermoplastic matrices, may also quicken the degradation rate of the composite materials.…”

From Regenerated Wood Pulp Fibers to Cationic Cellulose: Preparation, Characterization and Dyeing Properties

“…An alternative to cotton fibers can be offered by using forest-based raw materials, most often free from herbicides and insecticides, and requiring no irrigation [6], such as wood-based cellulose fibers [1] from cheaper paper grade kraft pulp fibers [8,9]. Viscose…”