Fabrication and Properties of Polyethylene/Cellulose Nanocrystal Composites

Abstract

a laboratory scale, many polymer/CNC nano composites have been prepared and were demonstrated to exhibit a significant improvement in mechanical properties over the parent polymers. However, the technological exploitation of CNCs as reinforcing filler will hinge on the question if or how well such laboratory-scale results can be achieved by technologically viable processes. Unfortunately, systematic studies that correlate processing, structure, and mechanical properties of CNC nanocomposites are rare. In a previous study we demonstrated that once CNCs are well dispersed in amphiphilic polymers such as poly(vinyl acetate) [11] or hydrophobic polymers such as low-density polyethylene (LDPE), [16] they can be subsequently reprocessed via melt-mixing and retained similar dispersion and mechanical reinforcement, as long as highshear mixing, which caused mechanical degradation of the CNCs, was avoided.It appears to be particularly difficult to fabricate composites of the rather polar CNCs in hydrophobic polymer matrices such as LDPE, as the polarity differenceThe preparation of nanocomposites of low-density polyethylene (LDPE) and cellulose nanocrystals (CNCs) isolated from cotton or produced in situ by the dispersion of microcrystalline cellulose (MCC) is reported. The hydrophobic matrix polymer and the rather polar filler particles appear to be difficult to mix, but it is shown here that composites with significantly improved mechanical characteristics and of homogeneous appearance can be produced using an organic-solvent-free two-step process. This is achieved by first mixing an aqueous slurry of an LDPE powder with an average particle size of <600 μm with aqueous suspensions of CNCs or MCC and removing most, but not all, of the water. Compounding such water-plasticized mixtures in a roller-blade mixer and subsequent compression-molding afford highly transparent films, whose room-temperature storage modulus is increased by a factor of 2.5 upon incorporation of 15% w/w CNCs or MCC. The results demonstrate that LDPE/nanocellulose composites with improved mechanical properties can be produced by an organic solvent-free process that appears to be scalable to industrial production scale.

Polymer nanocomposites with cellulose nanocrystals made by co‐precipitation

“…PU/CNC nanocomposites were also prepared by direct mixing in a roller blade mixer with a similar approach as described by Sapkota et al . The same mixer and conditions were used as for the dilution from a masterbatch, however for the direct mixing approach, neat polymer was first molten, and then freeze‐dried CNCs were slowly added to the polymer melt to a final concentration of 10% w/w.…”

Nanocomposites based on renewable thermoplastic polyurethane and chemically modified cellulose nanocrystals with improved mechanical properties

“…Besides the aspect ratio, the mechanical properties of these materials depend upon the intrinsic properties of both reinforcement filler and polymer matrix, the volume fraction of reinforcement, and the potential formation of a percolation network in which the fillers are arranged in a rigid, interconected network‐like structure instead of individual particles, reinforcing the matrix more efficiently . In addition to these factors, the filler–matrix and filler–filler interactions, filler orientation and surface area, the film processing method (e.g., casting and extrusion), and processing parameters influence the production of a nanocomposite with suitable filler distribution and dispersion within the polymer matrix, which in turn is essential for material performance …”

“…27 In addition to these factors, the filler-matrix and filler-filler interactions, filler orientation and surface area, the film processing method (e.g., casting and extrusion), and processing parameters influence the production of a nanocomposite with suitable filler distribution and dispersion within the polymer matrix, which in turn is essential for material performance. 21,[28][29][30] Some factors such as the tendency to agglomerate irreversibly upon drying because of the high hydroxyl content at the surface, poor wettability by nonpolar polymer matrices, high moisture absorption, low degradation temperature (ca. 200-220 C), and incompatibility with most polymer matrices tend to hamper or even prevent the production of CNC-containing nanocomposites featuring high-performance.…”

Cross‐Linkable Modified Nanocellulose/Polyester Resin‐Based Composites: Effect of Unsaturated Fatty Acid Nanocellulose Modification on Material Performances

“…Some of the major disadvantages of the NC‐reinforcing filler include moisture absorption, and its polar and hydrophilic nature, which inhibit homogeneous dispersion in nonpolar polymer matrices . Besides reducing NC's hydrophilic nature, the bonding strength between cellulose filler and UPe thermosetting resin is one of the most important factors for obtaining good reinforcement in the composite .…”