Polymers

High fiber loadings often cause a performance cliff in short-glass-fiber-reinforced thermoplastics because of fiber agglomeration. Herein, polybutylene terephthalate (PBT) composites reinforced with flat glass fibers (FGFR) and conventional circular glass fibers (CGFR) are systematically compared at loadings of 20–50 wt%. The flat fibers exhibit a specific surface area of 0.50 μm⁻¹, approximately 1.61 times that of the circular fibers (0.31 μm⁻¹). At 50 wt% loading, FGFR achieves a tensile strength of 115.92 ± 1.29 MPa and a notched impact strength of 13.07 ± 2.06 kJ/m², which are 11.4% and 29.7% higher than those of CGFR, respectively (p < 0.001 and p < 0.05, Welch’s t-test). In contrast, CGFR reaches its maximum tensile strength of 107.45 ± 3.84 MPa at 40 wt% and then decreases by 3.2% at 50 wt%; together with a significant quadratic (inverted-U) trend of the CGFR strength–loading curve (p < 0.001) and the significant FGFR–CGFR divergence at 50 wt%, this reversal marks the onset of the performance cliff. At 10 GHz and 50 wt% loading, FGFR exhibits a dielectric constant of 4.30 and a loss tangent of 0.014, which are 17.8% and 22.2% lower than those of CGFR, respectively, owing to suppressed interfacial polarization associated with the preferential layered arrangement of the flat fibers. Rheologically, as the fiber content increases from 20 to 50 wt%, the melt flow rate of FGFR decreases by approximately 35.5%, whereas that of CGFR decreases by approximately 60.5%. The modified Halpin–Tsai, Kelly–Tyson, Maxwell–Garnett, and Krieger–Dougherty models, incorporating fiber geometry and a unified agglomeration correction, semi-quantitatively capture the tensile, impact, dielectric, and rheological properties. These results demonstrate that flat-fiber cross-section engineering is an effective strategy for developing high-performance wave-transparent composites under high filler loadings.

Poly(bisphenol A carbonate) (BPA-PC) is an engineering thermoplastic whose recycling is hindered by its Code-7 classification and environmental BPA leaching. Here, we report water-soluble molecularly imprinted nanozymes for the selective depolymerization of BPA-PC under mild alkaline conditions. Synthesized within cross-linked surfactant micelles, the optimized nanozyme combines shape-complementary BPA-matched pockets with surface basicity, achieving a 72-fold rate enhancement over porcine pancreatic lipase. Fluorescence titrations with a soluble dansyl-labeled BPA-PC dimer confirm strong substrate recognition (K_a ~10⁶ M⁻¹). Gel permeation chromatography reveals uniform reductions of 52–55% across M_n, M_w, and M_z, indicative of a random endo-chain cleavage mechanism. On macroscopic BPA-PC films, the nanozyme induces pronounced cracking and surface erosion, whereas polyethylene terephthalate (PET) control films remain undamaged. Furthermore, the aqueous nanozyme retains ~75% of its initial catalytic activity across five consecutive degradation cycles following simple phase extraction. This study demonstrates that tailored, shape-complementary nanozymes provide a generalizable, selective biocatalytic alternative for the circular chemical recycling of recalcitrant engineering plastics.

Vertically printed fused deposition modelling (FDM) components exhibit pronounced surface irregularities on their sidewalls at the interfaces between deposited layers, while limited interlayer bonding can impair their tensile performance. Although laser polishing has shown potential to improve the surface quality of vertically printed FDM components, the combined influence of laser scan orientation relative to the printed layers and hatch distance on the surface integrity and mechanical response of PLA remains insufficiently understood. To address this gap, a novel methodology for determining hatch distance (H) is introduced, with H defined as 25%, 50%, 75%, and 100% of the experimentally measured groove width (GW). To maximize structural and surface performance, three scanning strategies, parallel (0°), perpendicular (90°), and oblique (45°) to the layer interfaces, were evaluated using ANOVA, regression models, and SEM analysis. The results demonstrate a fundamental synergy between scan orientation and melt-flow dynamics. At H = 25%, perpendicular scanning produced the largest Sa reduction (59%), whereas parallel scanning yielded the lowest Sdr (3.14%, compared with 20.74% for the as-printed raw surface). At the same H, the Sdr was 4.45% for perpendicular and 8.45% for oblique scanning. SEM analysis indicates that while all strategies eliminated the inherent layered texture, the oblique strategy (45°) additionally led to more thorough valley filling through melt flow from two adjacent peaks. Specific surface porosity was identified at modified interfaces, providing indications of gas entrapment and bubble expansion within the heat-affected zone (HAZ). Statistical height distribution (positive Ssk and Sku < 3) demonstrates that HAZ-driven surface rounding occurs across all orientations. The greatest improvement in tensile performance was observed with oblique scanning (45°) at H = 100%, where peak force increased by 11.2% relative to that of the raw material. Fractography indicates that this improvement originates from a preserved ductile skin-layer that delays delamination, shifting the failure mode toward localized internal fibre breakage. This work establishes scanning orientation as the primary determinant of topography, while hatch distance dictates homogenization intensity, offering a systematic framework for optimising the laser polishing of polymers.