Margaret Sobkowicz-Kline

Understanding the hydrolysis kinetics of mono(2-hydroxyethyl) terephthalate (MHET) and bis(2-hydroxyethyl) terephthalate (BHET) is essential for optimizing enzymatic recycling of poly(ethylene terephthalate) (PET). Herein, a comprehensive kinetic analysis of both nonenzymatic (autohydrolysis) and enzymatic hydrolysis of MHET and BHET is provided. Autohydrolysis experiments (40–75 °C) revealed comparable activation energies of 98.1 and 96.3 kJ mol–1 for MHET and BHET, respectively. BHET autohydrolysis was 6 to 8 times faster than MHET, a difference attributed to a higher pre-exponential factor. The catalytic enhancement of LCCICCG and IsMHETase enzymes was further evaluated. While LCCICCG accelerated both reactions, its advantage diminished significantly above 60 °C as autohydrolysis began to dominate. Conversely, IsMHETase exhibited exceptional specificity for MHET, achieving nearly 3 orders of magnitude acceleration relative to autohydrolysis at 45 °C, though it was less effective toward BHET than LCCICCG. The results provide kinetic parameters as quantitative baselines for designing optimized enzyme cocktails and multizone bioreactors for efficient PET depolymerization.

Enzymatic depolymerization has the potential to contribute to nylon waste recycling. However, the implementation of a viable industrial process still lags far behind progress in enzymatic polyester recycling. Here we review the current biocatalytic nylon recycling landscape, highlighting biochemical, structural, and materials science barriers that currently limit depolymerization extents. We detail efforts to identify, engineer, and characterize new nylon depolymerases, where currently even the best biocatalysts rarely exceed ~1 wt% conversion of solid polymer to products. Based on our analyses, we suggest that limited substrate accessibility due to substrate crystallinity and hydrogen bonding, rather than intrinsic enzyme inefficiency or instability, is the primary bottleneck to enhanced depolymerization. Guided by successes in polyester enzymatic recycling, we outline a research roadmap combining nylonase engineering with polymer pretreatment, chemo-enzymatic cascades, and process analyses to accelerate development of viable enzymatic nylon recycling processes. The alternative text for this image may have been generated using AI.

This study explores a mechanochemical strategy for polyethylene (PE) recycling using ultrahigh‐speed twin screw extrusion (TSE), focusing on the synergistic effects of high shear rates and catalyst incorporation to induce structural transformations. By systematically controlling specific mechanical energy (SME), a scalable equipment‐independent parameter, the transformation was investigated across two PE structural variations (linear and branched) and linear PE with and without additives. Structural, molecular, and rheological changes were characterized using Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and parallel plate rheology. Catalyst incorporation achieved intimate dispersion and enhanced chain scission, producing low molecular weight liquid and gaseous byproducts collected from the devolatilization zone. Thermogravimetric analysis (TGA) revealed substantial reductions in PE decomposition temperature following catalyst incorporation, attributed to still‐active catalyst sites and the formation of labile functional groups such as ethers and esters. These findings establish TSE as a process intensification approach for controlling PE depolymerization with potential as a preconditioning strategy for downstream chemical recycling. By investing mechanical energy upstream to improve polymer catalyst contact and reduce activation barriers, this approach offers a pathway to lower the thermal energy requirements of chemical recycling, contributing to more economically viable and environmentally sustainable polyolefin waste management at industrial scales.

Model-guided compatibilization of post-consumer rPP/rPE blend enables smooth film extrusion with simultaneous gains in strength and ductility.

The evolution of crystallinity resulting from stress imposed on a melt, known as flow-induced crystallinity, can strongly influence the mechanical and physical properties of semicrystalline polymers. This study investigates shear-induced crystallization by applying an ultrasonic field to the melt flow as it passes through dies with various geometries. A custom-built sonication die is employed for controlling the dynamic temperature and shear environment, resulting in molecular alignment and potential for flow-induced crystallization. Application of both conventional and ultrasonic shear rates at the equilibrium melt temperature of high-density polyethylene (HDPE) was investigated to accelerate crystallinity and manipulate the crystal morphology across the film in pursuit of improved mechanical and gas barrier properties without the need for additives or other polymer layers. The relationships among ultrasonic-assisted extrusion processing, polymer structure, and performance were analyzed using wide- and small-angle X-ray scattering (WAXS and SAXS), tensile testing, and oxygen transmission rate (OTR) analysis. Multiple linear regression models were implemented to predict the correlation among HDPE structure, process, and properties. Structural analysis revealed that both conventional and ultrasonic shear rates had the most significant influence on lamellar spacing and redistribution of rigid and soft amorphous fractions within the crystalline domains, ultimately dictating the mechanical and physical properties of the films. The goal is to explore the potential of the ultrasonic-assisted high crystallinity monolayer that can replace some of the functionality of complex, heterogeneous multilayer packaging with a single-material film having enhanced oxygen barrier properties.

The processing and performance of multilayer films containing post‐consumer recycled polypropylene (rPP1 and rPP2) materials are investigated to understand the effect of layer multiplying elements (LMEs), die temperature, virgin polypropylene (vPP%) content, and polyethylene (PE) contamination in flexible packaging applications. Three‐layer coextruded films were created with virgin polypropylene (vPP) consistently applied as the outer layers while the core layer comprised recyclates with varying concentrations of polyethylene as an unintended contaminant to polypropylene. To enhance layer uniformity and interfacial interaction, a layer multiplying element (LME) was employed to increase the number of coextruded film layers from 3 to 9. Tensile properties (elongation at break, yield stress, and modulus) were characterized in both machine direction (MD) and transverse direction (TD); after which, multiple linear regression analyses were conducted on 45 observations to model the effect of each factor. The results indicated that the LME significantly enhanced elongation at break in TD by 1280% strain, while temperature and vPP fraction also contributed positively to ductility in TD (+341% and +2373%, respectively). However, PE contamination had a substantial negative impact on elongation in MD (−2449%) underscoring its embrittling role due to lack of compatibility with the PP matrix. Critically, LME partially mitigated the negative PE effect via an interaction term (PE*LME), improving elongation in MD by +3101%. Scanning Electron Microscopy (SEM) revealed a distinct, regular pattern of alternating polyethylene (PE) and polypropylene (PP) domains forming ribbon‐like fibrillar structures. This unique morphological arrangement suggests a self‐organizing behavior driven by immiscibility and flow‐induced alignment under extrusion conditions. The presence of regular alternating domains at near equal concentrations implies a balance among shear‐driven orientation, phase separation kinetics, and crystallization phenomena, resulting in an ordered micro‐fibrillar structure. Importantly, both monolayer and multilayer films containing rPP2 or rPP1/rPP2 blends exhibited these aligned, ribbon‐like fibrils oriented in the machine direction (MD). SEM analysis of fractured specimens further indicated that brittle failure was often associated with interfacial delamination, particularly in recyclate‐rich regions, whereas ductile failure exhibited entangled reinforcing fibrils, suggesting improved energy absorption and interlayer cohesion. Understanding and controlling this self‐organized microstructure could significantly enhance processing stability, mechanical properties, and potential applications of recycled polyolefin blends, offering novel strategies for tailoring recyclate morphology and performance.