Impact of shredding degree on papermaking potential of recycled waste

The properties of paper products depend on the structure of the cellulose fibres therein. Although fibre properties in virgin pulps can be modified by a refining process, this is more difficult in pulp from recovered fibre, particularly waste from office shredders that tend to shorten fibres during shredding. The shorter fibres in shredded paper make it difficult to easily reconstitute them into high-quality paper products. Moreover, because of high energy usage during the recycling process and transportation inefficiencies, there is a need to determine how to responsibly shred paper to alleviate this environmental burden. With this in mind, the influence of initial fibre length on the tensile properties of paper was investigated. Changes in initial fibre length significantly influenced many pulp and paper properties. It was found that cutting the paper into pieces with an area less than 25 mm2 caused significant changes in the important morphological parameters of the fibres and a sharp decrease in the tensile properties of the reconstituted paper.

Influence of Initial Fibre Length and Content Used in the Injection Moulding of CFRP on the Properties of C/C and C/C-SiC Composites

The production of C/C-SiC composites comprises a three-stage process: forming (CFRP-composite), pyrolysis (C/C-composite) and liquid silicon infiltration (C/C-SiC). A new promising approach for the manufacturing of CFRP intermediate composites is the injection moulding of customised granulates (novolac resin, hardener, processing additives and short carbon fibre) produced by compounding technique. To date, a direct dosing of short carbon fibre into the compounder was technically not realisable due to fibre separation and electrostatic charging in the hopper. A possible substitute solution has been the direct feeding of a carbon fibre bundle from a roving into the compounder. However, this is associated with a severe damage of the fibres and an inaccurate adjustment of the fibres content. In the present article, new chopped carbon fibres provided with an adapted sizing to be directly dosed into the compounder are used. The fibres possess a predefined length of 3 and 6 mm and their content amounts to 50 and 58 wt.%. The influence of the initial fibre length and fibre content on the physical and mechanical properties of the resulting CFRP-, C/C-and C/C-SiC-composites is presented and discussed. In addition, the impact of fibre feeding procedure at the compounding stage on the microstructure is considered

Investigation of low consistency reject refining of mechanical pulp for energy savings

In this study, the effects of low consistency refining (LCR) energy and intensity on mechanical pulp properties have been studied for three different types of reject pulps (softwood TMP, softwood CTMP and hardwood CTMP), which were refined at varying intensity. Resulting pulp properties have been compared with high consistency refining (HCR) of the same reject pulps. For all furnish types, it was shown that LCR can develop pulp properties matching those developed through HCR with significantly less energy. The resulting pulp properties were found to be affected not only by refining intensity and energy, but also by initial fibre morphology. Pilot LCR trials demonstrated that high freeness reject pulp is initially insensitive to refining intensity as specific energy is applied. This enables the first stage of LCR to be carried out at a higher specific energy and intensity, which can reduce the number of stages of LCR required to reach a target quality. This work shows that low intensity LCR is capable of achieving the same tensile index as HCR pulp at a target freeness of 200 ml CSF.

Viscous propulsion in active transversely isotropic media

Taylor’s swimming sheet is a classical model of microscale propulsion and pumping. Many biological fluids and substances are fibrous, having a preferred direction in their microstructure; for example, cervical mucus is formed of polymer molecules which create an oriented fibrous network. Moreover, suspensions of elongated motile cells produce a form of active oriented matter. To understand how these effects modify viscous propulsion, we extend Taylor’s classical model of small-amplitude zero-Reynolds-number propulsion of a ‘swimming sheet’ via the transversely isotropic fluid model of Ericksen, which is linear in strain rate and possesses a distinguished direction. The energetic costs of swimming are significantly altered by all rheological parameters and the initial fibre angle. Propulsion in a passive transversely isotropic fluid produces an enhanced mean rate of working, independent of the initial fibre orientation, with an approximately linear dependence of the energetic cost on the extensional and shear enhancements to the viscosity caused by fibres. In this regime, the mean swimming velocity is unchanged from the Newtonian case. The effect of the constant term in Ericksen’s model for the stress, which can be identified as a fibre tension or alternatively a stresslet characterising an active fluid, is also considered. This stress introduces an angular dependence and dramatically changes the streamlines and flow field; fibres aligned with the swimming direction increase the energetic demands of the sheet. The constant fibre stress may result in a reversal of the mean swimming velocity and a negative mean rate of working if it is sufficiently large relative to the other rheological parameters.

Variability of flax fibre morphology and mechanical properties in injection moulded short straw flax fibre-reinforced PP composites

The influence of compounding and injection moulding on the initial variability and morphology of short straw flax fibres is determined and the mechanical properties for the injection moulded fibre reinforced composites are measured. It is found that the composition of the straw flax, flax fibre bundles and woody parts, together with the cutting process strongly affects the initial fibre morphology and its variability. In the initial fibres, small particles as well as long fibres with large width were found. A filter was used to reject the fibres with an aspect ratio below 15 before calculating statistics because these fibres have a negligible contribution to the composite reinforcement. After processing, the initial fibre length and width decrease strongly (−38% to −66% for length and −22% to −72% for width). Also, the variability is affected resulting in a standard deviation shifted towards lower fibre lengths and widths (−55% for length and −71% for width). The improvement of mechanical properties of the flax compound compared to the pure matrix material for the injection-moulded samples is found to be similar to the results for compounds with further processed flax fibres such as scutched and hackled fibres. An increase of tensile strength by 20% was found, for stiffness the increase is in the order of 50–70%. This indicates that despite the very large variability of the initial straw flax fibres and the strong changes of the variability in each processing step, a compound is obtained with improved mechanical properties.

Ground Hemp Fibers as Filler/Reinforcement for Thermoplastic Biocomposites

Mechanical properties (tensile, flexural, and impact) of ground hemp fibre polypropylene composites were investigated. Ground alkali-treated hemp fibre and noil hemp fibres with various initial fibre lengths were utilized to reinforce polypropylene matrix. Firstly, the microstructural and tensile characterizations of the two types of fibres were characterized using scanning electron microscope (SEM), Fourier transform infrared analysis (FTIR), and Dynamic Mechanical Analyser (DMA). Then, the fibres were ground into different lengths of 0.2, 0.5, 1, and 2 mm; composites containing 40 wt% short hemp fibre and 5 wt% maleic anhydride grafted polypropylene (MAPP) were fabricated by means of a twin screw extruder and an injection moulding machine. Finally, influence of hemp fibre type and initial hemp fibre length on tensile property of the composites were investigated. The results revealed that addition of either noil hemp fibre or normal treated hemp fibre into the pure polypropylene matrix increased the tensile strength almost twice and stiffness of the composites more than three times. Although noil hemp fibre composite indicated slightly lower mechanical properties than the normal alkali-treated fibre composites, the difference was not significant. The analysis of the results provided the optimum initial fibre length (powder) of 0.2 mm hemp polypropylene composite. The results can be extended to different types of natural fibres.