Influence of Printing Technique and Printing Conditions on Prints Recycling Efficiency and Effluents Quality

The aim of this work was to determine the influence of the conventional offset printing technique and digital electrophotography printing with liquid toner (LEP) on some optical properties of recycled fibres. A series of LEP prints was made with the variation of the negative voltage of the developing drum (−200 V, −280 V, −350 V, and −430 V) after calibration of the machine and achieving standard densitometry values. Besides deinkability aspects, the quality of wastewater effluents after process of prints recycling was observed in order to make a conclusion regarding how different printing techniques, conditions in printing process, and different types of inks can affect the wastewater effluents. Results of image analysis showed that by increasing the negative voltage of developing drum in LEP printing technique, the formation of large ink particles on handsheet from recycled pulp increases. Depending on the size of the negative voltage of the developing drum, under the same experimental conditions, handsheets made from LEP recycled fibres have lower whiteness gain, brightness gain, and ΔERIC of handsheets compared to those made from the offset prints. In addition, a certain correlation was found between IEERIC (ink elimination), chemical oxygen demand (COD), and total organic carbon (TOC) of wastewater effluents after recycling of LEP prints and offset prints as well. Organic water pollution parameters (COD and TOC) showed higher values in wastewater after recycling of offset prints compared to recycling of LEP prints.

Drainage in a Screw Press and Utilization of the Recovered Fibres after Thermo-Hydrolytic Disintegration of Waste Fibreboards

A thermo-hydrolytic disintegration process qualifies as a promising option for recycling the waste MDF and preserving the fibrous morphology of the recovered lignocellulosic fibre material. This study aims to include a drainage process between the thermo-hydrolytic disintegration and the further utilization of the recovered fibres (RF) obtained using a screw press for removing the disintegration water (DW). In this context, the chemical properties of the RF (pH, nitrogen content, formaldehyde emissions) and the DW (pH, formaldehyde, reducing sugars and equivalents and nitrogen contents) were analyzed. Moreover, the RF material was utilized to produce recycled MDF panels, solely containing the RF (100%) and hence supplanting 50% of the virgin fibres (VF). The recycled MDF portrayed significant reductions in the internal bond strength (IB), and flexural properties (MOR, MOE): in the case of MDF made from 100% recycled fibres, about half the strength was reduced, and in the case of MDF made from 50% recycled fibres, the strength was reduced by 20-25%. The Thickness swelling (TS) of the recycled MDF panels was similar, while the water uptake (WA) was higher than that of the original MDF. The recycled MDF panels also exhibited a higher content of formaldehyde and emission. The findings recommend the application of a screw press process for prompter drainage of the RF and to utilize the RF obtained in combination with the VF to achieve adequate mechanical properties rather than using the RF separately for the manufacturing of the recycled MDF panels.

Resizing Approach to Increase the Viability of Recycled Fibre-Reinforced Composites

Most recycling methods remove the essential sizing from reinforcing fibres, and many studies indicate the importance of applying sizing on recycled fibres, a process we will denote here as resizing. Recycled fibres are not continuous, which dissociates their sizing and composite lay-up processes from virgin fibres. In this study, commercial polypropylene and polyurethane-based sizing formulations with an aminosilane coupling agent were used to resize recycled glass and carbon fibres. The impact of sizing concentration and batch process variables on the tensile properties of fibre-reinforced polypropylene and polyamide composites were investigated. Resized fibres were characterized with thermal analysis, infrared spectroscopy and electron microscopy, and the tensile properties of the composites were analysed to confirm the achievable level of performance. For glass fibres, an optimal mass fraction of sizing on the fibres was found, as an excess amount of film former has a plasticising effect. For recycled carbon fibres, the sizing had little effect on the mechanical properties but led to significant improvement of handling and post-processing properties. A comparison between experimental results and theoretical prediction using the Halpin-Tsai model showed up to 81% reinforcing efficiency for glass fibres and up to 74% for carbon fibres.

The influence of artificial aging on recyclability and mechanical stability of pharmaceutical packaging

Recycling of wastepaper and packaging is one of the most desirable options for the purpose of preservation the environment and increasing the sustainability of production. Changes in customer behaviour have increased a demand for packaging materials, such as the growth of online shopping and/or demand for optimal sized packaging foods and medicines. During storage and transport, products can be exposed to different weather conditions, which ultimately affects their quality and disposal. Therefore, in this paper, the influence of moisture and temperature on the mechanical properties of pharmaceutical packaging as well as on the possibility of their recycling was investigated. The printed and formed pharmaceutical packaging was subjected to a process of accelerated aging in a chamber under the action of temperature and humidity, according to standard methods and defined conditions. Thereafter, the samples were subjected to mechanical testing to determine the effect of moisture on the mechanical properties. In addition, the impact of moisture on pharmaceutical packaging recycling performance was examined. Recycling was carried out in laboratory conditions by chemical deinking flotation according to the INGEDE 11 method, while the obtained recycled laboratory sheets were characterized by the determination of optical properties and the image analysis. It was found that the mechanical properties of the tested pharmaceutical packaging were deteriorated. From the results obtained by determination of the optical properties, in recycled samples the brightness decreases with aging. As the sample ages, the printing ink binds to the recycled fibres, so the ERIC is lower in recycled fibres obtained from non-aged samples compared to the old ones. The CIE coefficient b* is higher for samples obtained from recycling of aged pharmaceutical packaging than for samples obtained from recycling of non-aged samples, and aged recycled samples will be yellower than non-aged ones. Therefore, the whiteness is lower in recycled fibres obtained from aged samples. When measuring the image analysis, the obtained results show that the number of ink particles and their surface area are significantly reduced with the duration of aging time.

Influence of recycled fibres in paper on the UV stability of thermochromic prints

Recycled paper for environmentally conscious consumers can positively influence product selection. Thermochromic inks printed on such materials can give the product a special effect and increase its market competitiveness. During recycling, the paper is subjected to the action of various processes and chemicals, which later can have an impact on its stability, structural and optical properties. As is already known, the optical properties of paper affect the quality of the print. Thus, the goal of this study is to determine whether environmentally friendly substrates containing recycled fibres can be of the same quality as non-recycled substrates for the printing of thermochromic inks. For the research purposes, two commercially available thermochromic inks were printed on papers with a certain percentage of recycled fibres (33% and 100%). The results will show whether the percentage of fibres affects the colorimetic properties, dynamic characteristics of thermochromic inks and the UV stability during accelerated ageing of thermochromic prints.

Research on the recycled and hybrid fibre reinforced self-compacting concrete under flexure

In the present study the steel fibres coming from the end-of-life tires were applied as a reinforcement of self-compacting concrete. The influence of the recycled fibres and their mixture with glass or polypropylene fibres (hybrid mixes) on the flexural behaviour of SCC was tested. The research revealed that the dosage of 1.5% of recycled fibres is highly effective in the SCC matrix. The values of the residual flexural tensile strengths obtained in the tests classified the R-SCC to be used as a partial replacement of the conventional reinforcement. The addition of other types of fibres to R-SCC caused the further enhancement of flexural parameters with no negative effect on the distribution of the fibres in the mix.

A Study to Investigate the Mechanical Properties of Recycled Carbon Fibre/Glass Fibre-Reinforced Epoxy Composites Using a Novel Thermal Recycling Process

Manufacturing-based carbon fibre-reinforced polymer (CFRP) and glass fibre-reinforced polymer (GFRP) wastes (pre-consumer waste) were recycled to recover valuable carbon fibres (CFs) and glass fibres (GFs), utilising a novel thermal recycling process with a cone calorimeter setup. The ideal conditions to recycle both the fibres occurred at 550 °C in atmospheric pressure. The processing time in the batch reactor to recycle CFs was 20–25 min, and to recycle GFs it was 25–30 min. The recovery rate of the recycled CFs was 95–98 wt%, and for GFs it was 80–82 wt%. Both the recycled fibres possessed a 100–110 mm average length. The resin phase elimination was verified by employing scanning electron microscopy (SEM). Furthermore, the fibres were manually realigned, compression moulded at room temperature, and cured for 24 h by a laminating epoxy resin system. The newly manufactured CFRP and GFRP composites were continuous (uniform length from end to end), unidirectionally oriented (0°), and non-woven. The composites were produced in two fibre volumes: 40 wt% and 60 wt%. The addition of ≈20 wt% recycled CFs increased the tensile strength (TS) by 12%, young modulus (YM) by 34.27% and impact strength (IS) by 7.26%. The addition of ≈20 wt% recycled GFs increased the TS by 75.14%, YM by 12.23% and the IS by 116.16%. The closed-loop recycling approach demonstrated in this study can effectively recycle both CFRP and GFRP manufacturing wastes. Preserving the structural integrity of the recycled fibres could be an advantage, enabling recycling for a specified number of times.

Development of Wood Composites from Recycled Fibres Bonded with Magnesium Lignosulfonate

The potential of producing ecofriendly composites from industrial waste fibres, bonded with magnesium lignosulfonate, a lignin-based formaldehyde-free adhesive, was investigated in this work. Composites were produced in the laboratory using the following parameters: a hot press temperature of 210 °C, a pressing time of 16 min, and a 15% gluing content of magnesium lignosulfonate (on the dry fibres). The physical and mechanical properties of the produced composites were evaluated and compared with the European Standard (EN) required properties (EN 312, EN 622-5) of common wood-based panels, such as particleboards for internal use in dry conditions (type P2), load-bearing particleboards for use in humid conditions (type P5), heavy-duty load-bearing particleboards for use in humid conditions (type P7), and medium-density fibreboards (MDF) for use in dry conditions. In general, the new produced composites exhibited satisfactory mechanical properties: a bending strength (MOR) (18.5 N·mm−2) that was 42% higher than that required for type P2 particleboards (13 N·mm−2) and 16% higher than that required for type P5 particleboards (16 N·mm−2). Additionally, the modulus of elasticity (MOE) of composites (2225 N·mm−2) was 24% higher than that required for type P2 particleboards (1800 N·mm−2) and equivalent to the required MOE of MDF panels for use in dry conditions (2200 N·mm−2). However, these ecofriendly composites showed deteriorated moisture properties, i.e., 24 h swelling and 24 h water absorption, which were a distinct disadvantage. This should be further investigated, as modifications in the lignosulfonate formula used and/or production parameters are necessary.