Fibers

Cellulose fibers are abundant, renewable biopolymers with significant potential to replace petroleum-based materials, yet their high flammability limits their use in fire-sensitive applications such as protective packaging, electrical insulation, and interior building materials. In this study, softwood kraft fibers were phosphorylated without solvent or chemical pre-treatment using a molten urea/phosphoric acid system at 160 °C for 3 h (molar ratio of 6:3:1 for urea, H₃PO₄, and cellulose anhydroglucose units). After water quenching, disintegration, and washing, the modified fibers were blended with unmodified kraft fibers at various ratios (0, 20, 40, 60, 80, and 100 wt.%) to prepare standard paper handsheets (85–90 g/m²) dried at 120 °C. Fiber characterization confirmed successful phosphate ester grafting, yielding a phosphorus content of 5.9%, a nitrogen content of 8.7%, and a total charge increase from 92 to 4676 mmol/kg, while preserving fiber length (decreasing slightly from 2.04 to 1.93 mm). Thermogravimetric analysis revealed enhanced thermal stability, generating a residual char mass of 31.12 wt.% at 900 °C compared to 6.9 wt.% for untreated fibers. Handsheet apparent density varied from 0.260 g/cm³ for KFP60 to 0.316 g/cm³ for KFP100. Inter-fiber phosphate crosslinking during hot drying significantly improved mechanical performance, increasing maximum load from 10.27 N to 42.29 N and Young’s modulus from 39.77 to 99.78 MPa. Vertical flammability tests demonstrated that handsheets containing ≥60 wt.% phosphorylated fibers preserved their structural integrity after 30 s of flame exposure, whereas untreated handsheets burned completely. These results highlight phosphorylation as a scalable, halogen-free, and effective strategy for producing mechanically robust, fire-resistant cellulose materials.

The growing global demand for particleboards has generated large quantities of waste in recent years. This waste mainly arises from manufacturing processes, furniture industry offcuts, and end-of-life disposal. In response to waste management challenges, recycling and reuse technologies have advanced significantly. In this context, this study evaluates the feasibility of producing new particleboards using recycled particles obtained from laminated particleboard waste. Recycled particles were treated with hot water, oxalic acid, and a combination of both, and the most effective treatment was selected for panel production. Hot water treatment was insufficient to remove the cured UF resin and promote particle separation, whereas oxalic acid successfully achieved both. Three-layer panels were then manufactured using oxalic acid-treated recycled particles at incorporation levels of 0%, 25%, 50%, 75%, and 100% in the core layer. The average density, vertical density profile, and physical and mechanical properties, as well as the formaldehyde emissions, were assessed. The results showed that the inclusion of recycled particles did not significantly impact the average density or the vertical density profiles of the panels. Thickness swelling and water absorption after 24 h immersion were similar across all panels, indicating good dimensional stability. Internal bond (IB) strength showed no consistent trend with increasing recycled particle content, and panels with 75% recycled particles achieved the highest IB strength (0.48 MPa). In contrast, bending properties decreased when the proportion of recycled particles exceeded 25%. All panels satisfied the requirements of the LD-2 Grade for low-density particleboards specified by the ANSI A208.1-2022 standard. An increase in formaldehyde emissions was observed in panels containing more than 25% recycled particles compared to the control panels. These findings indicate that particleboards can incorporate up to 75% recycled particles in the core, while maintaining physical and mechanical properties comparable to those of the control panels.

Seams in upholstery fabrics are subjected to repeated mechanical loading during use, which may lead to progressive seam opening. This study evaluated a double-pass stitching variant in which the second pass follows the same nominal seam line as the first, with the aim of improving local seam stability without changing the basic seam geometry or adding reinforcing material. Four commercial upholstery fabrics were investigated: a plain-woven cotton–linen fabric (T1), a jacquard fabric containing chenille yarns (T2), a predominantly recycled-polyester twill fabric (T3), and a jacquard bouclé fabric (T4). The fabrics were tested in the warp and weft directions using single-pass and double-pass stitching. Three specimens per fabric × direction × stitching combination (48 in total) were subjected to a modified ISO 13936-2 procedure consisting of 10–180–10 N loading cycles up to 1000, with seam opening and specimen displacement recorded at 180 N every 100 cycles. Repeated-measures ANOVA evaluated the effects of fabric, loading direction, stitching variant, loading cycles, and their interactions. T1 was analysed descriptively because all weft specimens failed before the first scheduled measurement. For fabrics T2–T4, stitching variant had a strong effect on seam opening (p < 0.001; ηp² = 0.984), with the double-pass variant showing approximately 38–81% lower mean seam opening. At 1000 cycles, the largest difference was observed for T4 in the weft direction (13.97 ± 0.64 mm vs. 2.56 ± 0.38 mm). A significant Cycles × Stitching interaction (p < 0.001; ηp² = 0.504) showed different seam-opening development between the two stitching variants. The effectiveness of double-pass stitching depended on fabric type and loading direction, and inferential conclusions are limited to T2–T4 and the investigated loading conditions.