Recycling Oxidized Model Polyethylene Powder as a Degradation Enhancing Filler for Polyethylene/Polycaprolactone Blends

Polyethylene (PE) powder with different degrees of oxidation was prepared to model end-of life polyethylene that has been oxidized during processing and/or service-life. The nonoxidized and preoxidized PE powders were blended with PCL to evaluate the possibility to recycle PE powder in PCL blends. Good elongation at break was reached for all 25/75 (w/w) PE/PCL films and the elongation at break correlated well with the carbonyl index of the original PE powder, indicating that the oxidation of PE increased the interfacial adhesion with PCL and improved the blend properties. The preoxidized PE powder in combination with surfactant and pro-oxidant greatly accelerated the degradation rate of PCL as measured by molecular weight decrease during low temperature thermo-oxidative aging. This coincided with the fast initial increase in PE carbonyl index. The degradation accelerating effect was larger when preoxidized PE was blended with PCL as compared to when nonoxidized PE was added. However, the degree of preoxidation had minor impact on PCL degradation rate. Without PE powder the degradation rate of PCL was not enhanced by the addition of pro-oxidant and surfactant alone

Green Semi-IPN Hydrogels by Direct Utilization of Crude Wood Hydrolysates

Crude and unmodified acetylated galactoglucomannan containing wood hydrolysate (WH) was directly incorporated into a semi-interpenetrating network (semi-IPN) composed of up to 60% renewable polymers. Semi-IPNs were produced by a facile and green synthetic pathway through cross-linking modified carboxymethylcellulose in the presence of at least 30%(w/w) WH, via free radical copolymerization with acrylic acid and <i>N</i>,<i>N</i>′-methylenebis­(acrylamide). FTIR verified the presence of WH interlaced with CMC in the semi-IPN, and the highly porous microscopic structure of the networks was confirmed by SEM. The gelation process of these networks was monitored in situ, and their individual “gel point” (the <i>G</i>′-<i>G</i>″ crossover) was determined by in situ rheological measurements. Semi-IPN hydrogels with various swelling ratios (<i>Q</i> = 20–225) were obtained within 2.8–20 min of a cross-linking reaction

Ring-Closing Depolymerization: A Powerful Tool for Synthesizing the Allyloxy-Functionalized Six-Membered Aliphatic Carbonate Monomer 2‑Allyloxymethyl-2-ethyltrimethylene Carbonate

Ring-closing depolymerization is demonstrated to be a powerful synthetic methodology for the formation of six-membered functional aliphatic carbonate monomers, providing a rapid, straightforward, inexpensive, and green route for obtaining six-membered functional aliphatic carbonate monomers at a scale greater than 100 g. The utility of this technique was observed via the synthesis of the allyloxy-functionalized six-membered cyclic carbonate monomer 2-allyloxymethyl-2-ethyltrimethylene carbonate (AOMEC). The synthesis was performed in a one-pot bulk reaction, starting from trimethylolpropane allyl ether, diethyl carbonate, and NaH, resulting in a final AOMEC yield of 63%. The synthetic methodology is based upon the reversible nature of this class of polymers. The anionic environment produced by NaH was observed to be sufficient to mediate the monomer equilibrium concentration; thus, an additional catalyst is not required to induce depolymerization. 1,5,7-Triazabicyclo[4.4.0]­dec-5-ene (TBD) was demonstrated to be a very active catalyst for the ring-opening polymerization (ROP) of AOMEC, resulting in a rapid (<i>k</i>_p^app = 28.2 s^–1) and controlled polymerization with a low dispersity (<i><i>Đ</i></i> = 1.2). The availability and activity of the functionality of poly­(AOMEC)­s were established through subsequent postpolymerization functionalization via the UV-initiated thiol–ene chemistry of poly­(AOMEC) with 1-dodecanethiol and benzophenone as a radical initiator. The functionalization proceeded with high control and with a linear relation between the molecular weight and conversion of the unsaturation, revealing the high orthogonality of the reaction and the stability of the carbonate backbone. Hence, as a synthetic methodology, depolymerization provides a straightforward and simple approach for the synthesis of the highly versatile functional carbonate AOMEC. In addition, formation of the monomer does not require any solvents, reactive ring-closing reagents, or transition-metal-based depolymerization catalysts, thereby providing a “greener” route for obtaining functional carbonate monomers and polymers

Simultaneous Polymerization and Polypeptide Particle Production via Reactive Spray-Drying

A method for producing polypeptide particles via <i>in situ</i> polymerization of <i>N</i>-carboxyanhydrides during spray-drying has been developed. This method was enabled by the development of a fast and robust synthetic pathway to polypeptides using 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU) as an initiator for the ring-opening polymerization of <i>N</i>-carboxyanhydrides. The polymerizations finished within 5 s and proved to be very tolerant toward impurities such as amino acid salts and water. The formed particles were prepared by mixing the monomer, <i>N</i>-carboxyanhydride of l-glutamic acid benzyl ester (NCA_Glu) and the initiator (DBU) during the atomization process in the spray-dryer and were spherical with a size of ∼1 μm. This method combines two steps; making it a straightforward process that facilitates the production of polypeptide particles. Hence, it furthers the use of spray-drying and polypeptide particles in the pharmaceutical industry

Thermodynamic Presynthetic Considerations for Ring-Opening Polymerization

The need for polymers for high-end applications, coupled with the desire to mimic nature’s macromolecular machinery fuels the development of innovative synthetic strategies every year. The recently acquired macromolecular-synthetic tools increase the precision and enable the synthesis of polymers with high control and low dispersity. However, regardless of the specificity, the polymerization behavior is highly dependent on the monomeric structure. This is particularly true for the ring-opening polymerization of lactones, in which the ring size and degree of substitution highly influence the polymer formation properties. In other words, there are two important factors to contemplate when considering the particular polymerization behavior of a specific monomer: catalytic specificity and thermodynamic equilibrium behavior. This perspective focuses on the latter and undertakes a holistic approach among the different lactones with regard to the equilibrium thermodynamic polymerization behavior and its relation to polymer synthesis. This is summarized in a monomeric overview diagram that acts as a presynthetic directional cursor for synthesizing highly specific macromolecules; the means by which monomer equilibrium conversion relates to starting temperature, concentration, ring size, degree of substitution, and its implications for polymerization behavior are discussed. These discussions emphasize the importance of considering not only the catalytic system but also the monomer size and structure relations to thermodynamic equilibrium behavior. The thermodynamic equilibrium behavior relation with a monomer structure offers an additional layer of complexity to our molecular toolbox and, if it is harnessed accordingly, enables a powerful route to both monomer formation and intentional macromolecular design

Crucial Differences in the Hydrolytic Degradation between Industrial Polylactide and Laboratory-Scale Poly(L-lactide)

The rate of degradation of large-scale synthesized polylactide (PLA) of industrial origin was compared with that of laboratory-scale synthesized poly­(L-lactide) (PLLA) of similar molar mass. The structural discrepancy between the two material types resulted in a significant difference in degradation rate. Although the hydrolysis of industrial PLA was substantially faster than that of PLLA, the PLA material became less brittle and fragmented to a lesser extent during degradation. In addition, a comprehensive picture of the degradation of industrial PLA was obtained by subjecting different PLA materials to hydrolytic degradation at various temperatures and pH’s for up to 182 days. The surrounding environment had no effect on the degradation rate at physiological temperature, but the degradation was faster in water than in a phosphate buffer after prolonged degradation at temperatures above the <i>T</i>_g. The degree of crystallinity had a greater influence than the degradation environment on the rate of hydrolysis. For a future use of polylactide in applications where bulk plastics are generally used today, for example plastic packages, the appropriate PLA grade must be chosen based on the conditions prevailing in the degradation environment

Thiolated Hemicellulose As a Versatile Platform for One-Pot Click-Type Hydrogel Synthesis

A one-pot synthetic methodology for the thiolation of <i>O</i>-acetyl-galactoglucomannan (AcGGM) was developed to merge hemicellulose chemistry with “click” chemistry. This was realized by the AcGGM-mediated nucleophilic ring-opening of γ-thiobutyrolactone via the activation of the polysaccharide pendant hydroxyl groups. The incorporation of thiol functionalities onto the hemicellulose backbone was visualized by ¹H and ¹³C NMR spectroscopy and was assessed by an Ellman’s reagent assay of the thiol groups. The versatility of the thiolated AcGGM was elaborated and demonstrated by conducting several postmodification reactions together with hydrogel formation utilizing thiol–ene and thiol-Michael addition “click” reactions. The one-pot synthesis of thiolated AcGGM is a straightforward approach that can expand the applications of hemicelluloses derived from biomass by employing “click” chemistry

Innovative Approaches for Converting a Wood Hydrolysate to High-Quality Barrier Coatings

An advanced approach for the efficient and controllable production of softwood hydrolysate-based coatings with excellent oxygen-barrier performance is presented. An innovative conversion of the spray-drying technique into a coating applicator process allowed for a fast and efficient coating process requiring solely aqueous solutions of softwood hydrolysate, even without additives. Compared to analogous coatings prepared by manual application, the spray-drying produced coatings were more homogeneous and smooth, and they adhered more strongly to the substrate. The addition of glyoxal to the aqueous softwood hydrolysate solutions prior to coating formation allowed for hemicellulose cross-linking, which improved both the mechanical integrity and the oxygen-barrier performance of the coatings. A real-time scanning electron microscopy imaging assessment of the tensile deformation of the coatings allowed for a deeper understanding of the ability of the coating layer itself to withstand stress as well as the coating-to-substrate adhesion

Electroactive Hydrophilic Polylactide Surface by Covalent Modification with Tetraaniline

Covalent surface functionalization is presented as a versatile tool to increase the hydrophilicity and to introduce the electroactivity of polyester films. Acrylic acid and maleic anhydride were photografted onto a polylactide (PLA) surface with a “grafting from” method to increase the surface wettability, and the subsequent coupling of conductive aniline oligomer was used to introduce electroactivity to the PLA surface. The photopolymerization of maleic anhydride and acrylic acid and the coupling of aniline tetramer (AT) were characterized by FT-IR, UV, and TGA. The surface morphology of the PLA surface before and after modification was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A medium hydrophilic surface of PLA was achieved by surface modification with maleic anhydride, acrylic acid, and AT. An electrically conductive surface was obtained after grafting with AT, and the conductivity increased with increasing AT content on the surface. The hydrophilic and electroactive surface of polyesters while retaining their bulk properties offers new possibilities in biomedical applications, such as bone, cartilage, neural, and cardiovascular tissue engineering

Innovative Approaches for Converting a Wood Hydrolysate to High-Quality Barrier Coatings

An advanced approach for the efficient and controllable production of softwood hydrolysate-based coatings with excellent oxygen-barrier performance is presented. An innovative conversion of the spray-drying technique into a coating applicator process allowed for a fast and efficient coating process requiring solely aqueous solutions of softwood hydrolysate, even without additives. Compared to analogous coatings prepared by manual application, the spray-drying produced coatings were more homogeneous and smooth, and they adhered more strongly to the substrate. The addition of glyoxal to the aqueous softwood hydrolysate solutions prior to coating formation allowed for hemicellulose cross-linking, which improved both the mechanical integrity and the oxygen-barrier performance of the coatings. A real-time scanning electron microscopy imaging assessment of the tensile deformation of the coatings allowed for a deeper understanding of the ability of the coating layer itself to withstand stress as well as the coating-to-substrate adhesion