Improvement in the Thermomechanical Properties and Adhesion of Wood Fibers to the Polyamide 6 Matrix by Sequential Ball Milling Technique

The engineering thermoplastics industry has largely limited the use of natural fiber reinforcements due to their susceptibility to low-onset thermal degradation and water absorption. Therefore, in order to utilize these economically viable and environmentally friendly materials effectively through common composite fabrication methods such as hot pressing, safeguarding them from thermal degradation becomes essential. This work presents a viable industrially technique called sequential ball milling for processing unbleached softwood kraft pulp fibers (PF) with an engineering thermoplastics polyamide 6 (PA6) with high melting temperatures (>220 °C). An additional eco-friendly modification step that employs ball milling and cellulose nanocrystal (CNC) has been implemented in this study to enhance the mechanical properties of the composites. Special attention is given to fine-tuning key variables, such as milling duration and PF particle size, to produce optimal composites. Leveraging the ability of sequential ball milling to evenly distribute pulp fibers into PA6, a 160% increase in Young's modulus was achieved with the incorporation of 30 wt % PF. Importantly, the introduction of a 5 wt % CNC modifying agent elevated Young's modulus to 4.3 GPa, marking a 187% improvement over unmodified PA6. Diverse techniques, including rheological analyses, thermomechanical evaluations, morphological examinations, and assessments of moisture absorption, were utilized to validate the efficiency of the suggested processing approach and the modification phase.

Direct milling: Efficient, facile, and green method for processing fibrillated cellulose/polymeric nanocomposites with boosted thermomechanical and rheological performance

Bringing biobased nanomaterials into polymer manufacturing is essential to enhance polymers' properties and address the challenges posed by plastic waste. Using polymers such as polyamide 6 (PA6) in advanced industries, e.g., automotive sector, has been impeded as a direct consequence of their inability to meet the required mechanical properties. Herein, we utilize bio-based cellulose nanofibers (CNFs) to enhance the properties of PA6 by green processing, with no footprint on the environment. We address the issue of the dispersion of the nanofillers in polymeric matrices and demonstrate direct milling (cryo-milling and planetary ball milling) to facilitate a thorough integration of the components. Nanocomposites incorporating 1.0 wt% CNF, processed by pre-milling followed by compression molding, are shown to possess a storage modulus of 3.8 ± 0.2 GPa, Young's modulus of 2.9 ± 0.2 GPa, and ultimate tensile strength of 63 ± 3 MPa (all measured at room temperature). To show the superiority of direct milling in achieving these properties, other frequent approaches used to disperse CNF in polymers, such as solvent casting and hand mixing, are meticulously investigated and compared for the performance of their resulting specimens. The ball-milling method is demonstrated to provide PA6-CNF nanocomposites with excellent performance, better than solvent casting, with no associated environmental concerns.

Rheological and Crystallization Properties of ABS/PA6-Compatibilized Blends via In Situ Reactive Extrusion

ABS/PA6-compatibilized blends were prepared by in situ reactive extrusion method. The main objective was to evaluate the influences of the morphology and blend composition on the rheological and nonisothermal crystallization properties. The morphology of submicron-sized ABS droplets evenly dispersed in PA6 led to dilatant fluid behavior and a transition from elastic to viscous behavior in the low-frequency region. The crystallization results indicated that reactive blends had elevated crystallization temperatures and crystallization rates, which were due to the heterogeneous nucleation of the submicron-sized ABS particles. In addition, it was observed that the theory by Mo suitably described the nonisothermal crystallization process. The activation energy slightly decreased for ABS contents of 5 and 15 wt % and then increased for a content of 25 wt %, indicating that the ABS promoted the crystallization of the blends at appropriate contents.