Quality Changes of Low-Density Polyethylene (LDPE) Recyclates from the Pretreatment Process with a Cationic Surfactant and a Nonionic Surfactant as Cleaning Agents Upstream of Extrusion

Guo, Jinyang; Kim, Young‐Ju; Chong, Zhi Kai; Alassali, Ayah; Chacon, Jose Pablo; Gottschalk, Dieter; Kitzberger, Magdalena; Kuchta, Kerstin

doi:10.3390/pr10112174

Cited by 8 publications

(3 citation statements)

References 57 publications

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“…First, the mixing of the different pigments results in a dark or grayish color after the extrusion process, which lowers the market value of the recyclates [30]. Secondly, recyclates with printing ink mixed inside were reported to have lower tensile strength properties [39,40]. Finally, some ink components are not stable under the extrusion temperature of the mechanical recycling process (150-240 • C) [29,[41][42][43].…”

Section: Printing Ink As a Source Of Contaminationmentioning

confidence: 99%

“…Nine flakes were randomly selected from each sample, glued with colorless glue onto DIN A4 white print paper and scanned in a scanner (EPSON ET-588 The L-a-b values according to the CIELAB standard [73,74] were measured with a se developed program with Python 3.10, and the program code is given in Supplementa Material S2. The color change of the samples before and after the de-inking was calculat with the same method applied in previous de-inking studies [40,64,65,67]…”

Section: Evaluation Of the De-inking Effectmentioning

confidence: 99%

“…The L-a-b values according to the CIELAB standard [73,74] were measured with a selfdeveloped program with Python 3.10, and the program code is given in Supplementary Material S2. The color change of the samples before and after the de-inking was calculated with the same method applied in previous de-inking studies [40,64,65,67], shown in Equations ( 1) and (2).…”

Section: Evaluation Of the De-inking Effectmentioning

confidence: 99%

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Screening the Impact of Surfactants and Reaction Conditions on the De-Inkability of Different Printing Ink Systems for Plastic Packaging

Guo,

Luo,

Wittkowski

et al. 2023

Polymers

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One of the major applications (40% in Europe) of plastic is packaging, which is often printed to display required information and to deliver an attractive aesthetic for marketing purposes. However, printing ink can cause contamination in the mechanical recycling process. To mitigate this issue, the use of surfactants in an alkaline washing process, known as de-inking, has been employed to remove printing ink and improve the quality of recyclates. Despite the existence of this technology, there are currently no data linking the de-inking efficiency with typical printing ink compositions. Additionally, it is necessary to investigate the de-inking process under the process parameters of existing recycling plants, including temperature, NaOH concentration, and retention time. This study aims to evaluate the performance of commonly used printing inks with different compositions under various washing scenarios for plastic recycling in conjunction with different de-inking detergents containing surfactants or mixtures of surfactants. The results indicate that the pigments applied to the ink have no significant effect on the de-inking process, except for carbon black (PBk 7). Nitrocellulose (NC) binder systems exhibit high de-inkability (over 95%) under the condition of 55 °C and 1 wt.% NaOH. However, crosslinked binder systems can impede the de-inking effect, whether used as a binder system or as an overprint varnish (OPV). The de-inking process requires heating to 55 °C with 1 wt.% NaOH to achieve a substantial effect. Based on the findings in this work, breaking the Van der Waals forces, hydrogen bonds, and covalent bonds between the printing ink and plastic film is an essential step to achieve the de-inking effect. Further research is needed to understand the interaction between surfactants and printing inks, enabling the development of de-inkable printing inks and high-performance surfactants that allow for de-inking with less energy consumption. The surfactant and NaOH have a synergistic effect in cleaning the printing ink. NaOH provides a negative surface charge for the adsorption of the cationic head of the surfactant and can hydrolyze the covalent bonds at higher concentrations (>2 wt.%).

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Section: Printing Ink As a Source Of Contaminationmentioning

confidence: 99%

Section: Evaluation Of the De-inking Effectmentioning

confidence: 99%

Section: Evaluation Of the De-inking Effectmentioning

confidence: 99%

See 1 more Smart Citation

Screening the Impact of Surfactants and Reaction Conditions on the De-Inkability of Different Printing Ink Systems for Plastic Packaging

Guo,

Luo,

Wittkowski

et al. 2023

Polymers

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Utilization of Ultrasonication as a Method of Reducing Organic and Inorganic Contamination in Post‐Consumer Plastic Film Waste

Cecon,

Munshi,

Mukta

et al. 2024

Macro Materials & Eng

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Post‐consumer plastic film waste often carries organic and inorganic contaminants that challenge recycling processes and affect the quality of recycled products. An effective contaminant removal procedure through washing such single‐used plastic films (SUPFs) can address environmental and waste management concerns. This study compares the efficiency of different washing techniques in reducing SUPF contamination. To evaluate the efficacy of each washing technique, film samples collected from material recovery facilities are individually exposed to friction, ultrasonic‐assisted, and a combination of both washes. Thermal analysis indicates that the polymers' melting temperature, crystallization temperature, and crystallinity remain unaffected by the washing methods, demonstrating method aptness. Confocal laser scanning microscope images show that washing results in a cleaner sample surface. 91% ash reduction during the combined wash treatment indicates a high method efficiency compared to the individual friction and ultrasonic wash procedures. This is further validated by reducing characteristic contaminant IR bands (3600–3000, 1750–1600, and 1100–1000 cm−1). Elements of concern such as Cd, Cr, Hg, and Pb in SUPFs after each washing technique applied conform with regulations (<100 ppm) for packaging products. This research shows the novel ultrasonic washing reduces more contamination than friction with shorter wash times and no surfactants.

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Thermal degradation and hydrolysis depolymerization of printing ink components for plastic packaging in recycling processes: a review

Guo,

Luo,

Chong

et al. 2024

Front. Environ. Sci. Eng.

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This review covers the decomposition mechanisms of various printing ink binder resins, with a particular focus on their behavior under extrusion conditions in the mechanical recycling process of polyolefin (PO) based plastic packaging. Thermal degradation and hydrolysis of the nitrocellulose (NC) — the most used binder for flexographic surface printing on single-layer flexible plastic packaging, occur concurrently during the mechanical recycling process under 160–210 °C. For other printing ink binders, polyurethane (PU) noticeable degradation takes place between 200 and 300 °C, mostly above 250 °C. However, with the involvement of humidity, degradation by hydrolysis can start from 150 °C. A similar effect is also discovered with the cellulose acetate (CA) derivatives, which are thermally stable until 300 °C and can be hydrolyzed at 100 °C. The thermal stability of polyvinyl butyral (PVB) is not influenced by humidity, with thermal stability ranging from 170 to 260 °C, depending on different types. Ultraviolet (UV)-cured acrylics are thermally stable until 400 °C. The hydrolysis degradation can take place at room temperature. Moreover, this review covers the thermal stability of different colorants used for printing ink application and elaborates on several thermal-stable alternatives of some common colors. This study further reviews how the binder resin affects the quality of recyclates, revealing it to be not only induced by the degradation of the binder resin but also by the immiscibility between the plastic and binder resin. In advanced recycling processes, mainly selective dissolution-precipitation and pyrolysis, the presence of binder resin and its degradation products could still affect the quality of the product. This review accentuates the imperative need for in-depth research to unravel the impact of printing ink constituents on the quality of recycled products.

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Quality Changes of Low-Density Polyethylene (LDPE) Recyclates from the Pretreatment Process with a Cationic Surfactant and a Nonionic Surfactant as Cleaning Agents Upstream of Extrusion

Cited by 8 publications

References 57 publications

Screening the Impact of Surfactants and Reaction Conditions on the De-Inkability of Different Printing Ink Systems for Plastic Packaging

Screening the Impact of Surfactants and Reaction Conditions on the De-Inkability of Different Printing Ink Systems for Plastic Packaging

Utilization of Ultrasonication as a Method of Reducing Organic and Inorganic Contamination in Post‐Consumer Plastic Film Waste

Thermal degradation and hydrolysis depolymerization of printing ink components for plastic packaging in recycling processes: a review

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