Effect of Valley Beater Refining on Tensile Properties of Molded Pulps from Rice Straws

Rice straw, an abundant agricultural waste, is shown to be a promising resource for pulp and paper packaging manufacturing. In this study, rice straw pulps or cellulose fibers were extracted using a soda-AQ process and then the rice straw pulp slurries were refined by a Valley beater. The effect of refining time (15-60 min) on the pulp fiber characteristics was studied. It was found that both initial fiber length and width were decreased with refining time. The refined fibers became fibrillated, finer, and also more uniform in size confirmed by SEM. The pulp freeness (CSF) was reduced with increasing refining time as expected due to higher water-holding capacity of more fibrillated pulps. Then, the molded sheets were formed from the prepared rice straw pulps and examined. From tensile testing, the results indicated that the tensile properties of the molded sheets from the refined pulps were significantly enhanced (p < 0.05), thanks to an increase in fibrillated fiber surface area and inter-fiber bonding degree. The Valley beater refined rice straw pulp provided the molded sheet with the highest tensile index of 51.96 ± 4.08 Nm/g which are comparable to that of the sheets prepared from PFI mill refining process. The tensile properties of the current refined sheets were also in the acceptable range for typical commercial molded pulp packaging. In addition, the freeness values of the optimal Valley beater refined pulps are relatively high (348-423 ml), implying a benefit in forming process and manufacturing of pulp products.

True Strength of Ceramic Fiber Bundles: Experiments and Simulations

A study on the strength of ceramic fiber bundles based on experimental and computational procedures is presented. Tests were performed on single filaments and bundles composed of two fibers with different nominal fiber counts. A method based on fiber rupture signals was developed to estimate the amount of filament rupture during the test. Through this method, the fiber bundle true strength was determined and its variation with the initial fiber count observed. By using different load-sharing models and the single filament data as input parameter, simulations were also developed to verify this behavior. Through different approaches between experiments and simulations, it was noted that the fiber bundle true strength increased with the fiber count. Moreover, a variation of the fibers’ final proportion in the bundles relative to the initial amount was verified in both approaches. Finally, discussions on the influence of different load-sharing models on the results are presented.

Thermostabilizing annealing analysis of organomorphic preforms made of oxidized polyacrylonitrile

The simulation results of the thermal stabilization of polyacrylonitrile pressed organomorphic frame samples are presented. The local temperature maximum in the sample depth due to an exothermic oxidation reaction was confirmed. The possibility of the avalanche exothermic effect, which can lead to a sample burnout, is demonstrated theoretically. The analysis of the influence of the initial fiber oxidation degree on the sample temperature state have been carried out.

The Effect of Fiber Clusters and Voids on the Coalescence of Debonds in Polymer Matrix Composites

The objective of the current work is to conduct a systematic analysis on the effects of manufacturing induced defects such as random distribution of fibers and presence of voids in matrix on the damage initiation in polymeric composites. Upon infusing resin, the initial fiber configuration undergoes perturbation and results in a random distribution with pockets of resin rich areas and fiber clusters. In addition, this could result in micro voids (between the fibers in the bundle) and macro voids (between the fiber bundles). A novel methodology has been put forward to generate random distributions of fibers that would simulate different levels of perturbations in the manufacturing process resulting in different configurations of fiber clusters. An embedded Representative Volume Element (RVE) approach has been adopted in a finite element model to calculate the stress fields without artificial effects of the RVE boundary. Damage initiation is then analyzed using a previously proposed energy based criterion for cavitation in polymers.

Influence of the Initial Fiber Orientation on the Weld Strength in Welding of Glass Fiber Reinforced Thermoplastics

The welding factors are significantly lower in welding of fiber reinforced thermoplastics than in welding of unreinforced thermoplastics due to the fiber orientation in the weld. This paper presents results from investigations on the influence of the initial fiber orientation on the weld strength in hot plate and vibration welding for glass fiber reinforced polypropylene and polyamide 6. Injection molded specimens are compared to specimens with main initial fiber orientation being longitudinal and transverse to the joining direction. The results of CT analysis of the fiber orientation in the weld show the opportunity to achieve a higher weld strength by using specimens with fibers being initially oriented longitudinally to the joining direction. The influence of the initial fiber orientation in the parts to be welded on the weld strength in hot plate welding is more distinct than in vibration welding.