Reduction In Molecular Weight Research Articles

A kinetic scission model for molecular weight evolution in bioresorbable polymers

AbstractFurther development of bioresorbable devices for use in clinical applications, where they can reduce long term risks, has been hindered by the complex degradation mechanisms that bioresorbable polymers exhibit and the difficulty this causes in designing suitable devices. Furthermore, experimental degradation studies often take years to complete, and small changes to the design of the test sample may significantly alter the degradation behavior. Motivated by existing degradation models, we present a kinetic scission model to predict how the molecular weight distribution evolves as a function of degradation time for bioresorbable polymers. Here, a refined kinetic model has been developed to capture the autocatalytic effect of carboxylic acid ends created via chain scissions, and our framework accounts for reduction in molecular weight via the cleavage of monomers from chain ends and from scissions in the middle of the polymer chain. These developments allow for a more complete representation of the molecular weight distribution during degradation. Young's modulus is estimated by approximating the changes in entropy for the molecular weight distributions following previous so‐called “entropy spring” models. The results obtained are quantitatively compared to and calibrated with existing experimental data for PLGA films. Finally, the effect of the initial carboxylic acid end on the degradation behavior is explored.

Solid-state modification of tapioca starch using atmospheric nonthermal dielectric barrier discharge argon and helium plasma

Starch modification utilizes a substantial amount of water. This research aimed to investigate the effect of nonthermal dielectric barrier discharge (DBD) argon and helium plasma on tapioca starch's physicochemical properties and techno-functionality. Dry starch samples were treated with plasma generated from argon and helium gases at different voltage levels (10 and 15 kV) for 5, 10, and 15 min. The treatment did not destroy the starch’s crystalline structure, as evidenced by the birefringence under polarized light. Scanning electron micrographs showed dented starch granules. A marginal decrease in pH value of all treated samples was noted. A reduction in amylose and amylopectin molecular weight and increased reducing sugars were observed in the treated samples. Fourier transform infrared spectroscopy analysis showed a slight change in the 1047/1022 cm−1 absorbance ratio, indicating a change in short-range ordered degree of starch, while X-ray diffractometry showed a decrease in crystallinity. A significant reduction in peak viscosity, breakdown, and setback was observed. The gelatinized plasma-treated starch dispersion showed less shear-thinning and less thixotropic with increasing voltage and treatment times. This research proved that modification of starch in the solid-state using nonthermal plasma is feasible.

Additive Manufacturing of Anatomical Poly(d,l-lactide) Scaffolds

Poly(lactide) (PLA) is one of the most investigated semicrystalline polymers for material extrusion (MEX) additive manufacturing (AM) techniques based on polymer melt processing. Research on its application for the development of customized devices tailored to specific anatomical parts of the human body can provide new personalized medicine strategies. This research activity was aimed at testing a new multifunctional AM system for the design and fabrication by MEX of anatomical and dog-bone-shaped PLA samples with different infill densities and deposition angles. In particular, a commercial PLA filament was employed to validate the computer-aided design (CAD) and manufacturing (CAM) process for the development of scaffold prototypes modeled on a human bone defect. Physical-chemical characterization of the obtained samples by 1H-NMR spectroscopy, size exclusion chromatography (SEC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) demonstrated a small reduction of polymer molecular weight (~5%) due to thermal processing, as well as that the commercial polymer employed was a semicrystalline poly(d,l-lactide). Mechanical characterization highlighted the possibility of tuning elastic modulus and strength, as well as the elongation at break up to a 60% value by varying infill parameters.

Structural evolution of in situ polymerized poly(L-lactic acid) nanocomposite for smart textile application

This present study demonstrated the preparation of a highly crystalline anatase (ana) form of titanium oxide (TiO2) doped silk nanocrystal (SNC) nanohybrid (ana-TCS) of diameter (7.5 ± 1.4 nm) by the sol–gel method using titanium (IV) butoxide as the hydrolysis material. This prepared nanohybrid with surface hydroxyl groups acted as a co-initiator for the synthesis of poly(L-lactic acid) (PLLA)-g-ana-TSC nanocomposite with grafted PLLA chains via the in situ polymerization technique, using tin-octoate as a catalyst. The fabricated nanocomposite had a high number average molecular weight of 83 kDa with good processibility. This prepared nanocomposite was hydrophobic in nature, with a contact angle of 105°, which was further enhanced to 122 ± 1° when processed via electrospinning technique into a non-woven fabric. The prepared nanocomposite could degrade up to 43% methylene blue dye in 15 days. This nanocomposite showed no significant molecular weight reduction after 1 h of aqeous treatment, which could be attributed to its hydrophobic nature, inhibiting its degradation. However, 50% degradation was observed for the nanocomoposite whereas, PLLA demonstrated 25% degradation in 15 days, after its end-of-life. Thus, this study revealed that the in situ synthesized PLA-ana-TCS nanocomposite could be targeted for use as a hydrophobic, self-cleaning, dye-degradable fabric.

Oxidative degradation of UV-irradiated polyethylene by laccase-mediator system

Polyethylene (PE) is one of the most widely used plastics. However, the chemical inertness, inefficient recycling, and random landfilling of PE waste have caused serious pollution to the natural environment. In this study, a series of laccase-mediator systems (LMS) were constructed by combination of two laccases from Botrytis aclada (BaLac) and Bacillus subtilis (BsLac) with three synthetic mediators (ABTS, HBT, and TEMPO) to oxidize LDPE films (UVPE) pretreated with high-temperature UV irradiation. Scanning electron microscopy showed aging phenomena such as etching, fragmentation, and cracking on the surface of the UVPE films after LMS incubation. The FTIR results showed that LMS-UVPE added new oxygen-containing functional groups such as -OH, -CO, and CC. High-temperature gel chromatography confirmed that the average reduction in weight-average molecular weight (Mw) was approximately 40% for the BaLac experimental group. GC-MS analysis showed the presence of oxygen-containing products, such as aldehydes, ketones, and alcohols, in the reaction mixture. To verify the oxidation process UVPE degradation by LMS, we inferred three possible pathways by combined analysis of the oxidation products of LMS on UVPE and model substrates oleic acid and squalene.

Impact of Melt Processing Conditions on the Degradation of Polylactic Acid.

To reduce the degradation of polylactic acid (PLA) during processing, which reduces the molecular weight of PLA and its properties, prior studies have recommended low processing temperatures. In contrast, this work investigated the impact of four factors affecting shear heating (extruder type, screw configuration, screw speed, and feed rate) on the degradation of PLA. The polylactic acid was processed using a quad screw extruder (QSE) and a comparable twin screw extruder (TSE), two screw configurations, higher screw speeds, and several feed rates. The processed PLA was characterized by its rheological, thermal, and material composition properties. In both screw configurations, the QSE (which has a greater free volume) produced 3–4 °C increases in melt temperature when the screw speed was increased from 400 rpm to 1000 rpm, whereas the temperature rise was 24–25 °C in the TSE. PLA processed at low screw speeds, however, exhibited greater reductions in molecular weight—i.e., 9% in the QSE and 7% in the TSE. Screw configurations with fewer kneading blocks, and higher feed rates in the QSE, reduced degradation of PLA. At lower processing temperatures, it was found that an increase in melt temperature and shear rate did not significantly contribute to the degradation of PLA. Reducing the residence time during processing minimized the degradation of PLA in a molten state.

Electrocatalytic Upgrading of Biomass Fast Pyrolysis Oil

Attempts to electrocatalytically upgrade bio-oil have been made in recent years. Mostly, the ECH (Electrocatalytic Hydrogenation) experiments of bio-oil were done using fixed bed electrode configurations at room temperatures and low current densities (<100 cm-2). The main goal was to demonstrate the viability of ECH as a bio-oil stabilization strategy, mainly through reduction of carbonyl contents (aldehydes and ketones) which could cause polymerization. High temperature may promote condensation polymerization of fast pyrolysis oil, low-temperature ECH is therefore considered a promising approach to stabilize pyrolysis oil. However, recent advances in ECH of fast pyrolysis oil have shown the limited reductive upgrading chemistry (hydrogenation, hydrogenolysis, or hydrodeoxygenation) through this approach. This was mainly attributed to the complexity of fast pyrolysis oil and the restricted electrolysis operating conditions. Most of the published works in ECH of pyrolysis oil reported the reduction of carbonyl content into alcohols in the substrate rather than the hydrodeoxygenation of aromatics or phenolics. In this study, ECH of fast pyrolysis oil (FPO) in acidic electrolytes using SSER (Stirred Slurry Electrocatalytic Reactor) configuration was conducted for the first time. A compositional analysis suggested that the FPO sample contained water (29 wt.%) and detected monomers (38.5 wt.%), which comprise of carbohydrate derivatives (35.2 wt.%) and lignin derivatives (3.3 wt.%). Balance of water and monomers must be oligomers. Three polar organic solvents (e.g., ethanol, isopropanol, and acetone) were tested in a mixed aqueous and organic electrolyte with MSA solution. The electrolysis experiments were carried out for 4–30 h at constant cathodic current densities (I = -218 to -255 mA cm-2) and temperatures (50–60 oC). In all cases, decreases in the weight average molecular weight (Mw) and the number average molecular weight (Mn) were observed with prolonged reaction times. Temperature and catalyst loading contributed to faster depolymerization of the oligomers. Using different organic solvents (e.g., ethanol, isopropanol, acetone), the degree of depolymerization was about 33–37% after nearly 20 h reactions. Color changes in the catholyte FPO samples were observed in all cases after 18–25 h, turning from dark brown to light yellow. This observation supports the GPC results showing the molecular weight reduction after the ECH. In this study, compound distributions were determined based on ten functional groups, such as acids, alcohols, aldehydes, ketones, esters, furans, alkanes, aromatics, phenols, and guaiacols. In all cases, the reduction of ketones, aromatics, and guaiacols was noticed, while the alkanes content slightly increased. The most dramatic increases in esters content were observed when ethanol (17–25%) or isopropanol (19–32%) was used. This was attributed to esterification of carboxylic acids (mainly acetic acid) in the FPO with alcohols in the presence of MSA, which catalyzed the reaction. Reduction of p-eugenol to cerulignol (4-propylguaiacol) was the most noticeable in all cases, implying that the unsaturated bond in the allyl group is easily reduced under the ECH conditions. Significant increases in the cerulignol contents were achieved with all the different solvents: ethanol (0.5–4.9%), isopropanol (1.4–6.9%), and acetone (1.4–5.4%), based on the composition calculation normalized by the lignin-relevant compounds detected in the catholyte samples. ECH of FPO in SSER with organic solvents addition has demonstrated mild depolymerization of FPO oligomers, esterification, and reduction of carbohydrate and lignin derivative monomers which could potentially upgrade the quality of FPO for synthesis of hydrocarbon fuels.

Rapid biodegradation of high molecular weight semi-crystalline polylactic acid at ambient temperature via enzymatic and alkaline hydrolysis by a defined bacterial consortium

Biodegradation of polylactic acid (PLA) in the natural environment is usually slow. This study aims to develop a bacterial consortium that biodegrades semi-crystalline PLA films with high molecular weight, at an ambient temperature of 30 °C. PLA-degrading bacteria were enriched from polymeric wastes. Proteobacteria, Bacteroidia and Actinobacteria relative abundances were high during the PLA-enrichment process. Four isolated bacteria, Nocardioides zeae EA12, Stenotrophomonas pavanii EA33, Gordonia desulfuricans EA63, and Chitinophaga jiangningensis EA02, which synthesized PLA degradative enzymes such as protease, esterase and lipase were mixed as consortium EAc. PLA films inoculated with EAc showed biofilm formation (10.54 log CFU/cm2), molecular weight (Mv) reduction (61%), and weight loss (9.68%) after 35 days. The extent of biodegradation was significantly higher than that by individual strains. Decrease in PLA Mv fitted the first order kinetics with a rate constant of 0.028 d−1. UV spectroscopy of biodegraded PLA suggested the carbonyl bond cleavage, while substantial chain scissions in the ester backbone of PLA were detected by ATR-FTIR. The rapid PLA biodegradation was due to the synthesis of diverse hydrolases and increase in pH, which led to enzymatic and alkaline hydrolysis. Consequently, EAc consortium could be applied in general solid waste treatment facilities for PLA degradation.

The Impact of Reprocessing with a Quad Screw Extruder on the Degradation of Polypropylene.

During mechanical recycling, polypropylene typically is reprocessed using a single- or twin-screw extruder. The degradation of polypropylene during this reprocessing reduces the polymer’s molecular weight and, consequently, limits the performance of the recycled resin. This work investigated the impact of a quad screw extruder (QSE), which has greater free volume, on the reprocessing of an impact copolymer polypropylene. To mimic the recycling process, the polypropylene was subjected to three processing cycles using a QSE and a comparable twin-screw extruder (TSE) operated at three screw speeds. The reprocessed materials were characterized for their rheological, morphological, and mechanical properties. For both extruders, increasing the number of reprocessing cycles and the screw speed resulted in higher melt flow indices, decreases in zero-shear viscosity, and shifting of the crossover points for the storage and loss moduli, which indicate reductions in the molecular weight and narrowing of the molecular weight distribution of the polypropylene. The QSE exhibited greater reductions in molecular weight compared to the TSE, probably due to the higher stresses associated with the three intermeshing points along its screws. Reprocessing caused a significant reductions in the Izod impact strength of the reprocessed polypropylene, which correlated with reductions in the particle size and particle size distribution of the dispersed rubbery phase in the polypropylene during reprocessing.

Effect of the immobilization of pectinase on the molecular weight distribution of pectin oligosaccharides obtained from citrus pectin

Current sustainability guidelines require industrial byproducts to be returned to the production cycle. One of the most important byproducts for agriculture and food production is pectin, which can be hydrolyzed to obtain pectin oligosaccharides (POS), with potential use as prebiotics. One of the challenges in POS production is the modulation of their molecular weight since those between 1 and 3 kDa exhibit higher prebiotic activity. In this work, a pectinase preparation was used for pectin hydrolysis, evaluating the effect of enzyme immobilization on the molecular weight distribution of the obtained POS. The pectinase preparation immobilized on functionalized silica with amino and glyoxyl groups and expressed 88.6 U per g of support. Enzyme immobilization improves thermal resistance at 50 °C and pH 4.0 compared to soluble pectinase. Immobilization also influences pectin hydrolysis and thus the POS generation, increasing yield by 10% when the immobilized pectinase was used. Interestingly, pectinase immobilization resulted in an average of 2.5 kDa for obtained POS.In contrast, soluble pectinase resulted in a continuous decrease of POS molecular weight over hydrolysis time. This difference could be attributed to the enzyme confinement on the porous silica, limiting the reduction in molecular weight of POS, probably because the immobilized enzyme exhibits higher diffusional restrictions than free enzymes. Our results help to understand and design an efficient and sustainable process to produce tailored prebiotic molecules from agro-industrial byproducts.

Towards a better understanding of synergistic enzyme effects during refining of cellulose fibers

Refining of cellulose fibers is essential for reaching desired paper properties, yet highly energy demanding. Enzymes like endoglucanases (e.g. EndoC) are increasingly used to reduce energy consumption during pulp refining. However, prediction of the enzyme effect is still a major concern, considering the high variety of commercially available enzyme formulations, containing a range of different enzymes. In this study, synergisms of xylanases and β-glucosidases in combination with endoglucanases purified from enzyme formulations were studied and related to their refining performance. Size exclusion chromatography with multi-angle laser light scattering (SEC-MALLS) of carboxymethylcellulose revealed that a narrow size distribution and a high reduction in molecular weight are beneficial characteristics for refining. SEC-MALLS of hardwood pulp resulted in pronounced formation of low molecular weight fractions (log MW 4.3) for most efficient refining enzymes. Application of enzyme formulations and combinations of endoglucanase EndoC with β-glucosidase or xylanase using Fourier-transform infrared spectroscopy (FTIR) revealed synergistic effects that promoted degradation of amorphous parts of cellulose. Laboratory refining trials on hardwood pulp confirmed the increase in degree of refining and tensile index after addition of xylanase and β-glucosidase. Surface plasmon resonance (SPR) analysis resulted in strong binding of endoglucanases to regenerated cellulose, which correlated to refining performance.

A Fucan Sulfate with Pentasaccharide Repeating Units from the Sea Cucumber Holothuriafloridana and Its Anticoagulant Activity.

A fucan sulfate (HfFS) was isolated from the sea cucumber Holothuria floridana after proteolysis-alkaline treatment and purified with anion-exchange chromatography. The molecular weight (Mw) of HfFS was determined to be 443.4 kDa, and the sulfate content of HfFS was 30.4%. The structural analysis of the peroxidative depolymerized product (dHfFS-1) showed that the primary structure of HfFS was mainly composed of a distinct pentasaccharide repeating unit -[l-Fuc2S4S-α(1,3)-l-Fuc-α(1,3)-Fuc-α(1,3)-l-Fuc2S-α(1,3)-l-Fuc2S-α(1,3)-]n-. Then, the “bottom-up” strategy was employed to confirm the structure of HfFS, and a series of fucooligosaccharides (disaccharides, trisaccharides, and tetrasaccharides) were purified from the mild acid-hydrolyzed HfFS. The structures identified through 1D/2D NMR spectra showed that these fucooligosaccharides could be derivates from the pentasaccharide units, while the irregular sulfate substituent also exists in the units. Anticoagulant activity assays of native HfFS and its depolymerized products (dHf-1~dHf-6) in vitro suggested that HfFS exhibits potent APTT-prolonging activity and the potencies decreased with the reduction in molecular weights, and HfFS fragments (dHf-4~dHf-6) with Mw less than 11.5 kDa showed no significant anticoagulant effect. Overall, our study enriched the knowledge about the structural diversity of FSs in different sea cucumber species and their biological activities.

Oxidative degradation of pre-oxidated polystyrene plastics by dye decolorizing peroxidases from Thermomonospora curvata and Nostocaceae

Biodegradation of PS has attracted lots of public attentions due to its environmental friendliness. However, no specific PS degrading enzyme has been identified yet. Dye decolorizing peroxidases (DyPs) are heme-containing peroxidases named for the ability to degrade a variety of organic dyes. Herein, the abilities of two DyPs from Thermomonospora curvata (TcDyP) and Nostocaceae (AnaPX) to degrade PS were evaluated. Preoxidation methods by ultraviolet (UV) irradiation and chemical oxidants were developed to initially activate C-C bonds in the PS skeleton. DyPs degradation caused obvious etching and enhanced hydrophilicity of UV-PS films, and also generated new CO and C-OH groups. The cleavage of activated C-C bonds by DyPs was experimentally proven by analyzing the degradation products of UV-PS and model substrates. Furthermore, better pre-oxidation was obtained by using chemical oxidants KMnO4/H2SO4 and mCPBA to oxidize PS materials in dissolved state. And AnaPX exhibited stronger degradation effects on KMnO4/H2SO4-PS and mCPBA-PS by causing greater changes in functional groups CO, C-O, -OH groups and substituted benzenes and higher molecular weight reductions of 19.7% and 31.0%, respectively. To our knowledge, this is the first report on the identification of PS-degrading enzymes that provides experimental evidence.

Fracture mechanisms of additively manufactured polylactide: Effect of in vitro hydrolytic degradation

This is the first study considering the effect of in vitro hydrolytic degradation at 37 °C on fracture mechanism of the most important aspect of additive manufacturing – the interface between layers. Specimens were tested transversely (failure between layers) and longitudinally (failure directly through extruded filaments) under testing conditions similar to those in the human body (submerged at 37 °C). Feature of fracture surface, including striations and localised ductility, significantly changed when degradation caused a reduction in molecular weight below 40 kDa from the initial 240 kDa or an increase in crystallinity above 12%. Such changes indicated a transition from more ductile to more brittle fracture during degradation.

Poly(arylene sulfide)s via nucleophilic aromatic substitution reactions of halogenated pyromellitic diimides

AbstractNucleophilic aromatic substitution (SNAr) reactions are exploited to prepare poly(arylene sulfide)s (PAS's) via the reaction of bis‐thiolates and dibrominated pyromellitic diimide (PMDI) derivatives. Small‐molecule model studies reveal the reaction is well‐defined and proceeds in quantitative yield in practical times at room temperature. Variation in comonomer feed ratios allowed some control over target polymer molecular weights in the step polymerization, but control was likely limited by the relatively poor polymer solubility in the dipolar aprotic solvents typically employed to promote SNAr reactions. One substitution pattern produces a steric “pocket” around the PMDI units, inducing a peculiar solubility trend in halogenated solvents; that is, greatly reduced solubility in CHCl3 relative to CH2Cl2 and C2H2Cl4. One example small‐molecule readily dissolves in CHCl3 at room temperature, then rapidly grows poorly soluble crystals revealed by single‐crystal XRD to contain CHCl3 molecules in the steric pockets. Finally, the recently demonstrated depolymerization of phthalonitrile‐based PAS's via ipso substitution with monothiolates as chain scission agents yields quantitative molecular weight reduction to monomeric species from the polymers reported here.

Ripening induced degradation of pectin and cellulose affects the far infrared drying kinetics of mangoes

The quality parameters of mangoes change during ripening, which has a vital impact on processing characteristics. Effects of ripening stage (four stages from the lowest to highest degree—RS-1, RS-2, RS-3, RS-4) on cell wall polysaccharides and far infrared drying kinetics of mangoes were investigated. As ripening progressed, the water-soluble pectin contents increased by 213.5%; while the chelate-, sodium carbonate-soluble pectin and hemicellulose contents decreased by 44.0%, 59.5% and 65.8%, respectively. Moreover, the molecular weight reduction confirmed the degradation of pectin. These further caused the alteration of cell wall structure and changes in water distribution. Meanwhile, the drying time of mangos with different ripeness were in the order: RS-3 > RS-4 > RS-2 > RS-1. It correlated with the degradation of cell wall polysaccharides, the destruction of cell wall and the increases in free water during ripening. The ripeness classification could effectively improve the uniformity and efficiency of fruits drying processing.

Mechanical properties and highly-ordered structural analysis of elastic poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] fibers fabricated by partially melting crystals

Poly[( R )-3-hydroxybutyrate- co -( R )-3-hydroxyvalerate] (P(3HB- co -3HV)) elastic fibers were prepared at temperatures close to or below the melting temperature by partially melting thin crystals with no associated reduction in molecular weight. The obtained fibers exhibited elastic properties and good long-term stability of their mechanical properties, even after aging for 330 days. Cycle tests were conducted with simultaneous in-situ wide-angle X-ray diffraction and small-angle X-ray scattering using synchrotron radiation to investigate the mechanisms governing these fibers’ elasticity. It was determined that the main factor contributing to the elasticity is the reversibility between the random coil structure of tie molecules and the planar zigzag conformation of molecular chains in response to loading and unloading. • P(3HB- co -3HV) elastic fibers were prepared at temperatures below T m . • Elastic fibers exhibited good long-term stability of their mechanical properties. • Cycle tests were conducted with simultaneous in situ WAXD/SAXS measurements. • The generation mechanism of elasticity is proposed.

Effect of Pretreatment and High Hydrostatic Pressure on Soluble Dietary Fiber in Lotus Root Residues

High hydrostatic pressure (HHP) can enhance the physicochemical properties of soluble dietary fiber (SDF) from fruit and vegetable residues including hydration properties, emulsibility, and rheological properties, while the pretreatment methods such as solid-water suspension status are ignored all along. Here, three groups of lotus root residue (LRR) for HHP treatment (400 MPa, 15 min) were prepared: the fresh lotus root residue (FLRR), FLRR mixed with water (FLRR + W), and dried FLRR suspended in water at the same solid/water level with FLRR + W (DLRR + W). As a control, non-HHP-treated FLRR was tested. Results showed that FLRR + W obtained the highest SDF yield and presented a honeycomb structure which was not observed in other LRR samples. In addition, properties of SDF extract from FLRR + W changed most significantly, including not only the enhancement of SDF yield, the improvement of hydration properties, and the reduction of molecular weight but also the increase of thermal and rheological stability. Principal component analysis (PCA) profile illustrated that the difference of LRR-water system contributed 27.6% to the SDF physicochemical changes, and SDF from DLRR + W distinguished it from the other samples with mannose, ribose, and glucuronic acid, indicating that the drying procedure also played a role in the HHP treatment focusing on the sugar constitution. Therefore, the solid-water suspension status is a noteworthy issue before HHP treatment aiming at SDF modification.

Backbone Degradation of Polymethacrylates via Metal-Free Ambient-Temperature Photoinduced Single-Electron Transfer.

Polymeric materials comprised of all-carbon backbones are ubiquitous to modern society due to their low cost, impressive robustness, and unparalleled physical properties. It is well-known that these materials often persist long beyond their intended usage lifetime, resulting in environmental accumulation of plastic waste. A substantial barrier to the breakdown of these polymers is the relative chemical inertness of carbon-carbon bonds within their backbone. Herein, we describe a photocatalytic strategy for cleaving carbon-based polymer backbones. Inclusion of a low mole percent of a redox-active comonomer allows for a dramatic reduction in polymer molecular weight upon exposure to light. The N-(acyloxy)phthalimide comonomer, upon reception of an electron from a single-electron transfer (SET) donor, undergoes decarboxylation to yield a backbone-centered radical. Depending on the nature of this backbone radical, as well as the substitution on neighboring monomer repeat units, a β-scission pathway is thermodynamically favored, resulting in backbone cleavage. In this way, polymers with an all-carbon backbone may be degraded at ambient temperature under metal-free conditions.

Simulated Recycling of Polypropylene and Maleated Polypropylene for the Fabrication of Highly-Filled Wood Plastic Composites

In this study, polypropylene [PP] and maleic anhydride grafted polypropylene [MAPP] were reprocessed from one to three times to simulate recycling. 30 wt % of the reprocessed PP and MAPP were compounded with 70 wt % wood filler to fabricate highly filled wood plastic composites [WPCs]. The neat and composite samples were produced using a batch mixer and injection molder. The effect of recycling and maleation of PP was analyzed using light scattering, nuclear magnetic resonance, rheology, microscopy, and other physical/mechanical properties. While thermomechanical processing may lead to chain scission reactions, shown by a reduction in melt viscosity and weight-average molecular weight, the observed changes are minor and did not change the bulk properties significantly. The repeated reprocessing allowed for the incorporation of up to 70 wt % wood flour [WF] to fabricate the highly filled WPC while the maleation allowed for better interactions and the composite’s strength. Overall, the WPCs with maleic anhydride displayed appealing physical properties due to their increased tensile properties and a lack of oxidation or significant level of degradation. This indicates that the maleation of reprocessed PP could be an important and effective strategy to reduce virgin and petroleum-based MAPP while revitalizing mechanical properties for WPCs.