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Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping
Thesis (MEng)--Stellenbosch University, 2026.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613935128018944 |
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| access_status_str | Open Access |
| author | Tshitshi, Ayabonga |
| author2 | Gorgens, Johann |
| author_browse | Gorgens, Johann Tshitshi, Ayabonga |
| author_facet | Gorgens, Johann Tshitshi, Ayabonga |
| author_sort | Tshitshi, Ayabonga |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2026. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/135721 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:44:02.133Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/135721 Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping Tshitshi, Ayabonga Gorgens, Johann Tyhoda, Luvuyo Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Thesis (MEng)--Stellenbosch University, 2026. Tshitshi, A. 2026. Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/7f6818dd-39d7-4172-905a-f06d31288428 Wet-strength sacks (WS Sacks) and liquid packaging board (LPB) are paper-based packaging materials used for potato bags and milk or juice cartons, respectively. Despite having high-quality softwood fibres characterised by long fibre length, these materials have the lowest recycling rates in South Africa. Wet-strength sacks are reinforced with wet-strength resins, primarily polyamide-epichlorohydrin (PAE), forming water-insoluble bonds that hinder repulping. In LPB, paperboard is laminated between plastic and aluminium foil layers, further complicating fibre recovery. This study aimed to establish optimal repulping conditions for WS Sacks and LPB to improve fibre recovery, evaluating pulp yield, fibre length, and filtrate quality, to assess industrial viability. Repulping experiments of PAE-based WS Sacks and LPB were conducted at 60 oC using a laboratory-scale Helico repulper operating at 750 rpm. For WS Sacks, dual chemical dosing was applied, using sodium hydroxide to increase pH to 10.5, followed by sodium persulphate to promote PAE degradation. Optimal repulping conditions were determined using the steepest ascent method and central composite design, investigating consistency (3-9%), time (30-300 minutes), and persulphate dosage (1-12%). Optimal consistencies of 8% (WS Sacks) and 6% (LPB) were identified. For LPB, maximum pulp yield (68%) was achieved after 60 minutes, with longer repulping durations offering no significant improvement. Wet-strength sacks required 180 minutes to reach high pulp yields of 85-90%, beyond which yield gains decreased, and throughput dropped below an industrial benchmark of 0.73 ton/hour. Optimal persulphate dosages of 6%, 12%, and 9.7% were determined for three sack materials. No fibre shortening occurred, with fibre lengths remaining at ≈2.00 mm (WS Sacks) and ≈1.50 mm (LPB). Residual PAE remained in small WS Sacks reject flakes (<10×10 mm), which exhibited limited further disintegration. Mixed plastic-aluminium LPB rejects with fibre traces showed elevated higher heating values (39.65 MJ/kg), volatile matter (73.77%), and total carbon content (63%), indicating suitability for pyrolytic conversion into energy-rich products. WS Sacks filtrates exhibited high conductivity (>3000 μS/cm) and low pH (<5), exceeding typical paper recycling mill limits, while LPB filtrates remained within acceptable ranges (400-600 μS/cm; pH 7-8). Blended feeds of WS Sacks and LPB were tested at varying ratios, with the highest pulp yield (82.00%) achieved at a 2:1 WS Sacks:LPB ratio, 8% consistency, 6% persulphate, and 180 minutes at 60 oC. After scaling, the experimental repulping optima corresponded to 12-16% consistency and 90 minutes for WS Sacks, and 9-12% and 30 minutes for LPB, falling within the operating region of the Helico repulper of Mpact Springs Mill. While industrial WS Sack repulping is limited, optimal LPB conditions indicated lower consistency and longer repulping time than current industry practice (≈18%, 10-20 minutes). Dual chemical dosing during WS Sacks repulping may pose operational challenges in mills with single-chemical dosing systems, and high ionic load and acidic effluents may require additional water treatment. Nevertheless, this study demonstrated that WS Sacks and LPB can be repulped in existing paper recycling mills equipped with Helico repulpers, indicating industrial viability and highlighting an opportunity to enhance fibre recovery and recyclability for their improved beneficiation. Masters 2026-04-08T13:55:05Z 2026-04-08T13:55:05Z 2026-03 Thesis https://scholar.sun.ac.za/handle/10019.1/135721 en Stellenbosch University 162 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Tshitshi, Ayabonga Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping |
| title | Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping |
| title_full | Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping |
| title_fullStr | Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping |
| title_full_unstemmed | Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping |
| title_short | Evaluating the recyclability of wet-strength sacks and liquid packaging board through repulping |
| title_sort | evaluating the recyclability of wet strength sacks and liquid packaging board through repulping |
| url | https://scholar.sun.ac.za/handle/10019.1/135721 |
| work_keys_str_mv | AT tshitshiayabonga evaluatingtherecyclabilityofwetstrengthsacksandliquidpackagingboardthroughrepulping |