Polymer-Cellulose Composites via Solid-State Shear Pulverization
INVENTION: Process for producing polymer-cellulose composites with enhanced properties.
ADVANTAGES: A scalable process to produce well dispersed polymer-cellulose composites having enhanced properties, without need of compatibilizing agents.
SUMMARY: Cellulose provides many opportunities to improve the physical properties of a range of polymers. Various composites have been devised, and performance results vary with cellulose purity and scale size. Cellulose composites also provide an excellent green alternative material. However, concerns common to such materials include fiber uniformity, aggregation and/or interaction with the polymer component. Thus, there remains an on-going search for an alternate approach to effective dispersion, to realize the benefits of polymer/cellulose composites.
This invention affords polymer/cellulose composites and methods for their preparation that overcome various deficiencies of the prior art. Solid-state shear pulverization (S3P) is a unique established process to compatiblize diverse materials without the addition of compatibilizing agents. S3P processing of polymer and cellulose mixtures yields composites with well-dispersed polymer wetted cellulose fibers.In polypropylene /cellulose composites, S3P incorporation of a small quantity of fiber greatly improves tensile properties. Addition of 5wt % cellulose increases the composite modulus by 60% relative to neat PP, with little impact on the tensile strength. When 30wt % cellulose is incorporated into PP, the modulus doubles (Figure 1). These large improvements were achieved without compatibilizing additives. As the cellulose content increases, the fibers become better dispersed, with polymer wetting the fiber surfaces, in contrast to previous reports of the incompatibility of PP and cellulose fibers.
The reduction of oxygen permeability caused by the presence of cellulose fibers is shown in Figure 2. At low cellulose content (5 10 wt%) there is little decrease in the permeability. However, at higher cellulose loadings, 20 wt% cellulose, oxygen permeability coefficient was reduced over 25%.
Inclusion of cellulose fibers in PP enhances crystallization kinetics with the fibers acting as nucleating agents. Pulverization of these composites leads to increased nucleation of crystallization similar to PP/cellulose systems that have been compatibilized with maleic anhydride.
In general, the mechanical properties of the S3P processed poly(lactic acid)/cellulose composites are similar to those reported in the literature. With increasing cellulose content, the modulus remains mostly unchanged. However the PLA/cellulose composite oxygen barrier properties are improved. Composites with low levels of cellulose remain similar to the PLA homopolymer. With 20 wt% cellulose the permeability coefficient is significantly decreased ~30%. Application of S3P to polymer / cellulose composite formation provides a direct process to enhance polymer properties with this common fiber.
STATUS: A patent application has been filed.
John Torkelson, Amanda Flores
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