Molybdenum disulphide—A traditional external lubricant that shows interesting interphase properties in pulp-based composites

Compression molded composites were prepared through a water-assisted mixing of an aqueous suspension of poly(ethylene-co-acrylic acid), additive, and pulp fibers [thermomechanical pulp (TMP) or dissolving pulp (DP)]. The lubricating additives used were magnesium stearate (MgSt) and molybdenum disulphide (MoS2). The composite materials had dry pulp contents ranging from 30 to 70 wt% and 5\ua0wt% additive relative to the weight of the pulp. The adsorption of the additives onto the fibers was confirmed by scanning electron microscopy and energy dispersive X-ray analysis. DMA showed that MgSt and MoS2 gave similar interphase properties for the TMP samples at all loading contents, but the combination of MgSt and MoS2 improved the overall properties of the DP-based composites. The tensile modulus, at 70 wt% fiber content (TMP or DP), increased compared to the matrix by a factor of 6.3 and 8.1, without lubricants, and by a factor of 8 and 10.7, with lubricants, respectively. The increase in melt viscosity observed for the lubricated samples was greater for the TMP-based samples containing MoS2. At a lubricant content of 5\ua0wt%, in 30 wt% TMP, the MoS2 behaved as both a lubricant and compatibilizer

Mechanical and Thermal Properties of Mixed PE Fractions from Post-Consumer Plastic Packaging Waste

The functional properties of recycled post-consumer flexible polyethylene packaging waste have been studied using materials collected and sorted at a large-scale facility in Sweden. The studied fraction was used both as received and after simple laboratory washing in water with added sodium hydroxide at 40 \ub0C. The materials were melt-compounded with a twin-screw extruder using two different temperature profiles and two screw configurations and injection-molded into slabs, whose thermal and mechanical properties were assessed. The results showed that the mechanical properties of injection-molded samples were not changed significantly either by the washing or by the temperature or screw configuration used in the compounding. Washing reduced the viscosity and molecular mass to a minor extent. As expected, the ash content of the compounded pellets was reduced by washing. The thermo-oxidative stability decreased with increasing compounding temperature and with washing

Washing Post-Consumer Flexible Polyethylene Packaging Waste

The mechanical and thermal properties of injection-molded recycled polyethylene were studied, specifically with respect to the influence of large-scale washing and melt-compounding of polyethylene from post-consumer packaging waste. Three types of materials were studied: those taken after sorting, after sorting and washing, and after sorting, washing, and melt-compounding, including melt-filtration, all from a large-scale material flow. The materials were further processed on a laboratory scale and compared. The results showed that large-scale washing significantly reduced thermo-oxidative stability, as well as molar mass and melt viscosity. The degradation during large-scale washing made the material susceptible to further degradation in the subsequent extrusion compounding, as shown by the differences in compounding at 240 and 200 \ub0C using a high-shear screw configuration. The compounding parameters, screw configuration, and compounding temperature did not influence the stiffness and strength of the unwashed and large-scale-washed materials, but the elongation-at-break varied, specifically, with the increased temperature. Washing had an influence on the mechanical properties as well, and the unwashed material provided molded samples with stiffness measurements of approximately 550 MPa, whereas the large-scale-washed material provided stiffness of approximately 400 MPa. The strength measurements were approximately 15 MPa for samples made of both unwashed and large-scale-washed material, and the elongation-at-break measurements were between 50 and 150%. The large-scale-washed and compounded materials had very different mechanical properties, with stiffness measurements of approximately 320 MPa, strength of approximately 20 MPA, and elongation-at-break of approximately 350%. The significantly different mechanical properties of the large-scale-washed and compounded materials were likely due to the melt-filtration included in the compounding through the removal of metal and rubber particles, and they may also have been due to the compatibilizing and stabilizing additive used in the compounding

Melt Processing of Ethylene-Acrylic Acid Copolymer Composites Reinforced with Nanocellulose

To investigate the impact of process design factors such as number of passes, screw design and screw type, a poly(ethylene-co-acrylic acid) and a masterbatch containing 40 vol% nanocellulose were compounded using a twin-screw extruder with two different screw configurations. The 20 vol% composite pellets obtained, containing nanocellulose of different morphologies, cellulose nanofibrils and cellulose nanocrystals, were re-extruded several times to study the effect of re-extrusion. The compounded pellets were extruded into films using a single-screw extruder. These films contained aggregates of the nanocellulose material, which was reduced in size upon re-extrusion leading to an improvement in properties of the composites. With the best combination of process factors, the Young\u27s modulus and stress at break of the composites increased by factors of 10 and 1.6, respectively. The presence of a strong network of the cellulosic entities was observed qualitatively using melt rheology upon re-extrusion. Re-extrusion had a negligible effect on the crystallinity of the composites. POLYM. ENG. SCI., 2020. (c) 2020 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers

The thermo-oxidative durability of polyethylene reinforced with wood-based fibres

Aiming at better understanding the ageing behaviour of cellulose composites, the accelerated thermo-oxidative ageing of polyethylene reinforced with two types of wood-based cellulose fibres was studied. Materials were prepared by extrusion mixing of either un-stabilized or stabilized polyethylene reinforced with 5 and 20 vol % cellulose content. The materials were extruded into strips and then aged at 90\ub0C in circulating air. The effect of accelerated ageing up to 31 days was assessed by oxidation induction time and mechanical properties in tension. The results indicated that the added cellulose fibres did not increase the degradation of the composites during this ageing. Reinforcement with 20 % cellulose fibre having a 28 % lignin content together with 0.005 % Irganox 1010 antioxidant resulted in a remarkable improvement in the resistance against accelerated thermo-oxidation, compared to the pure polyethylene with added antioxidant. The findings of increased lifetime of LDPE by addition of wood-based reinforcement is of great interest, since the durability aspect is crucial to understand and predict before usage in commercial applications and especially as structural composites

Rheological and functional properties of mechanically recycled post-consumer rigid polyethylene packaging waste

ABSTRACT: The properties of recycled post-consumer rigid polyethylene packaging waste were studied, using sorted waste washed in the laboratory with water alone and with added detergent, and compared with large-scale high-intensity washed flakes. The washed flakes were compounded using three different temperature profiles in a twin-screw extruder and then injection molded. A higher compounding temperature reduced the thermo-oxidative stability, the average molecular mass, and the viscosity of the samples. Rheological measurements suggested that changes in chain branching occurred at different compounding temperatures. The strength and the elongation at break were also influenced by the compounding temperature in both the molten and solid states. Detergent washing maintained the thermo-oxidative stability in contrast to washing with water. The large-scale washed samples had a relatively high thermo-oxidative stability, a higher melt elasticity, and a lower elongation at break in both the molten and solid states than the laboratory-scale washed samples. The thermal properties, melt elasticity, Young’s modulus, yield stress, and yield strain of the samples were not, however, significantly affected by either the compounding temperature or the washing medium and intensity. The results indicated that recycled post-consumer rigid polyethylene packaging waste has properties that can support further applications in new products

Water-assisted extrusion and injection moulding of composites with surface-grafted cellulose nanocrystals – An upscaling study

The large-scale surface modification of cellulose nanocrystals (CNC) was carried out to produce CNC-containing composites, in a scale of 3 kg, using industrial-scale melt processing techniques such as twin-screw extrusion and injection moulding. Two different polymer matrices, ethylene-acrylic acid copolymer (EAA) and low-density polyethylene (LDPE), were reinforced with 10 wt% unmodified cellulose nanocrystals (CNC) or surface-treated CNC, where a 2-hydroxyproyl-N-diallyl group had been grafted onto the sulphate half-ester groups on the CNC surfaces. This was achieved by mixing an aqueous CNC dispersion and the polymer pellets directly in the twin-screw extruder followed by a second dry compounding step prior to shaping by injection moulding. The injection-moulded materials were characterized with respect to their mechanical properties and thermal stability. The addition of 10 wt % CNC resulted in all cases in an increase in the yield strength and stiffness by 50–100%, most significantly for the EAA based composites. There were indications of the presence of a stable interphase and a percolating network in the EAA-based materials, according to dynamic-mechanical measurements. A reduction in thermal stability was observed for the melt-processed samples containing diallyl-modified CNC and discoloration in the EAA based samples

Water-assisted melt processing of cellulose biocomposites with poly(ε-caprolactone) or poly(ethylene-acrylic acid) for the production of carton screw caps

Composites in 25 kg batches were compounded of cellulose nanocrystals (CNC) and thermomechanical pulp (TMP) and shaped into caps at industrial facilities on a pilot-plant scale. Some of the material was also injection molded into plaques to compare the effect of laboratory-scale and pilot-scale compounding of poly(ethylene-co-acrylic acid) (EAA7) and poly(caprolactone) composites reinforced with 10\ua0wt% CNC and TMP. The materials compounded under laboratory-scale conditions showed a different morphology, improved mechanical properties, and a higher viscosity, than the materials compounded on a pilot-scale. In some cases, the rheological properties of the melts indicated the presence of a relatively strong percolating cellulosic network, and the interphase region between the cellulose and the matrix appears to be important for the mechanical performance of the composites. After the compounding on a pilot scale, both the length and width of the pulp fibers was reduced. The TMP provided better reinforcement than the CNC possibly due to the higher aspect ratio

Cellulose nanofibril-reinforced composites using aqueous dispersed ethylene-acrylic acid copolymer

In order to explore the reinforcing capabilities of cellulose nanofibrils, composites containing high contents of cellulose nanofibrils were prepared through a combination of water-assisted mixing and compression moulding, the components being a cellulose nanofibril suspension and an aqueous dispersion of the polyolefin copolymer poly(ethylene-co-acrylic acid). The composite samples had dry cellulose nanofibril contents from 10 to 70 vol%. Computed tomography revealed well dispersed cellulose fibril/fibres in the polymer matrix. The highest content of 70 vol% cellulose nanofibrils increased the strength and stiffness of the composites by factors of 3.5 and 21, respectively, while maintaining an elongation at break of about 5%. The strength and strain-at-break of cellulose nanofibril composites were superior to the pulp composites at cellulose contents greater than 20 vol%. The stiffness of the composites reinforced with cellulose nanofibrils was not higher than for that of composites reinforced with cellulose pulp fibres. Graphical Abstract: [Figure not available: see fulltext.]

Composites with surface-grafted cellulose nanocrystals (CNC)

Hydroxyazetidinium salts were used to surface-modify cellulose nanocrystals (CNC) by grafting the salts onto the sulphate ester groups on the CNC surfaces. The grafting was confirmed by ζ-potential measurements and by the thermal degradation behaviour of the modified CNC. The thermal stability (onset of degradation) of the CNC was improved by the surface modification (almost 100\ua0\ub0C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10\ua0wt%) with an ethylene-based copolymer as matrix were produced by compression moulding. The thermal stability of the composites was not, however, markedly improved by the surface grafting onto the CNC. It is suggested that this is due to a degrafting mechanism, associated with the alkaline character of the system, taking place at high temperatures. Model experiments indicated, however, that this did not occur at the conditions under which the composites were produced. Furthermore, in the case of a reference based on pH-neutralised polymeric system and modified CNC, an upward shift in the onset of thermal degradation of the composite was observed. The addition of the CNC to the polymer matrix had a strong influence of the mechanical performance. For example, the tensile modulus increased approximately three times for some systems when adding 10\ua0wt% CNC. The surface grafting of the hydroxyazetidinium salts appeared mainly to affect, in a positive sense, the yield behaviour and ductility of the composites. The results of the mechanical testing are discussed in terms of interactions between the grafted units and the matrix material and between the grafted groups