Cross-linking Of Chains Research Articles

Cross-Linked Polyolefins through Tandem ROMP/Hydrogenation.

Cross-linked polyolefins have important advantages over their thermoplastic analogues, particularly improved impact strength and abrasion resistance, as well as increased chemical and thermal stability; however, most strategies for their production involve postpolymerization cross-linking of polyolefin chains. Here, a tandem ring-opening metathesis polymerization (ROMP)/hydrogenation approach is presented. Cyclooctene (COE)-co-dicyclopentadiene (DCPD) networks are first synthesized using ROMP, after which the dispersed Ru metathesis catalyst is activated for hydrogenation through the addition of hydrogen gas. The reaction temperature for hydrogenation must be sufficiently high to allow mobility within the system, as dictated by thermal transitions (i.e., glass and melting transitions) of the polymeric matrix. COE-rich materials exhibit branched-polyethylene-like crystallinity (25% crystallinity) and melting points (Tm = 107 °C), as well as excellent ductility (>750% extension), while majority DCPD materials are glassy (Tg = 84 °C) and much stiffer (E = 710 MPa); all materials exhibit high tensile toughness. Importantly, hydrogenation of olefins in these cross-linked materials leads to notable improvements in oxidative stability, as saturated networks do not experience the same substantial degradation of mechanical performance as their unsaturated counterparts upon prolonged exposure to air.

Cholesterol-Bearing Polysaccharide-Based Nanogels for Development of Novel Immunotherapy and Regenerative Medicine.

Novel functional biomaterials are expected to bring about breakthroughs in developing immunotherapy and regenerative medicine through their application as drug delivery systems and scaffolds. Nanogels are defined as nanoparticles with a particle size of 100 nm or less and as having a gel structure. Nanogels have a three-dimensional network structure of cross-linked polymer chains, which have a high water content, a volume phase transition much faster than that of a macrogel, and a quick response to external stimuli. As it is possible to transmit substances according to the three-dimensional mesh size of the gel, a major feature is that relatively large substances, such as proteins and nucleic acids, can be taken into the gel. Furthermore, by organizing nanogels as a building block, they can be applied as a scaffold material for tissue regeneration. This review provides a brief overview of the current developments in nanogels in general, especially drug delivery, therapeutic applications, and tissue engineering. In particular, polysaccharide-based nanogels are interesting because they have excellent complexation properties and are highly biocompatible.

The impact of synergistic action of methacrylic acid/zinc oxide/carbon nanotubes on metal Friction and wear

The continuous operation of essential refining equipment, internal mixers, leads to wear on their end faces, resulting in an increased gap between the mixer chamber and the end face. This, in turn, causes material leakage, reducing mixing efficiency and adversely impacting rubber performance. Therefore, investigating metal wear on the mixer's end face during the mixing process is essential. Scholars have introduced dynamic covalent bonds into rubber molecular chains, bestowing self-repairing capabilities upon the materials. This innovation has significant implications for extending rubber lifespan and lowering production costs. It involves adding methacrylic acid (MAA) and excess zinc oxide (ZnO) to construct an ionic crosslinking network, limiting covalent crosslinking of rubber molecules and enabling in-situ polymerization of MAA/ZnO, resulting in self-repairing properties. However, it is crucial to consider corrosive wear induced by MAA's strong acidity on metals. This study combines MAA, ZnO, and multi-walled carbon nanotubes (MWCNTs) through mechanical mixing to create a composite material called zinc methacrylate (ZDMA)/MWCNTs/rubber. The research investigates the in-situ synthesis mechanism of MAA and ZnO and the synergistic mechanism of ZDMA and MWCNTs. The study analyzes the impact of MWCNTs additive amount on the frictional wear of the internal mixer's metal end face. During the mixing process, ZDMA is grafted and polymerized onto rubber's macromolecular chains, forming ionic pairs with strong electrostatic interactions, creating a primarily reversible supramolecular network dominated by ion crosslinking. This ion crosslinking network, along with the three-dimensional mesh structure of MWCNTs, establishes a stable spatial structure within the rubber matrix. The study reveals that increasing the MWCNTs content to 3 phr reduces the aggregation of SiO2 particles and ZDMA granules within the rubber matrix, resulting in reduced friction coefficients, roughness, and wear rates of the metal. However, exceeding 3 phr of MAA content leads to excessive MWCNT aggregation within the rubber matrix, increasing wear rates, roughness, and friction coefficients due to hindrance of rubber macromolecular chain crosslinking and reduced SiO2 particle dispersion within the rubber matrix. These findings provide valuable insights into the dynamics of frictional wear in internal mixers.

Partial fluorinated silica incorporated with tuneable alkyl cross-linker based multi-cationic alkaline membrane for vanadium redox flow battery

Herein, we report partial fluorinated polymer (poly(vinylidene fluoride-co-hexafluoropropylene); PVDF-co-HFP)-based multi-cationic (quaternary ammonium, and imidazolium groups) cross-linked (tuneable carbon chain cross-linker) anion exchange membrane (AEM) incorporated with functionalized silica to avoid any structural deformations under harassed environment. Prepared membranes are cross-linked using different cross-linking agents, to study the effect of cross-linker chain length on the membrane performance. Incorporation of functionalized silica by acid-catalyzed sol-gel process improves membrane properties and stabilities. Reported PVIm-C10-APS AEM shows high conductivity (7.20 × 10−2 S/cm), and ion exchange capacity (1.48 meq/g). Well optimized positively charged PVIm-C10-APS AEM exhibits extremely low permeability of vanadium cations because of “Donnan exclusion” (9.80 × 10−7 cm2/s). During VRFB operation, PVIm-C10-APS AEM exhibits 98.10% coulombic efficiency (CE) and 77.60% voltage efficiency at 100 mA/cm2 without any significant deterioration up to 300 charge-discharge cycles. Further, PVIm-C10-APS membrane also shows >1.50 V OCV and 345 mW/cm2 peak power density at 400 mA/cm2. Reported AEM has been bench-marked with other membranes reported in the literature, and assessed as a promising material for VRFB or membrane separator for energy devices.

Development of High-Performance Coconut Oil-Based Rigid Polyurethane-Urea Foam: A Novel Sequential Amidation and Prepolymerization Process.

The utilization of coconut diethanolamide (p-CDEA) as a substitute polyol for petroleum-based polyol in fully biobased rigid polyurethane-urea foam (RPUAF) faces challenges due to its short chain and limited cross-linking capability. This leads to compromised cell wall resistance during foam expansion, resulting in significant ruptured cells and adverse effects on mechanical and thermal properties. To address this, a novel sequential amidation-prepolymerization route was employed on coconut oil, yielding a hydroxyl-terminated poly(urethane-urea) prepolymer polyol (COPUAP). Compared to p-CDEA, COPUAP exhibited a decreased hydroxyl value (496.3-473.2 mg KOH/g), an increase in amine value (13.464-24.561 mg KOH/g), and an increase in viscosity (472.4-755.8 mPa·s), indicating enhanced functionality of 34.3 mgKOH/g and chain lengthening. Further, COPUAP was utilized as the sole B-side polyol in the production of RPUAF (PU-COPUAP). The improved functionality of COPUAP and its improved cross-linking capability during foaming have significantly improved cell morphology, resulting in a remarkable 4.7-fold increase in compressive strength (132-628 kPa), a 3.5-fold increase in flexural strength (232-828 kPa), and improved insulation properties with a notable decrease in thermal conductivity (48.02-34.52 mW/m·K) compared to PU-CDEA in the literature. Additionally, PU-COPUAP exhibited a 16.5% increase in the water contact angle (114.93° to 133.87°), attributing to the formation of hydrophobic biuret segments and a tightly packed, highly cross-linked structure inhibiting water penetration. This innovative approach sets a new benchmark for fully biobased rigid foam production, delivering high load-bearing capacity, exceptional insulation, and significantly improved hydrophobicity.

Electrical Resistivities of PVA/Activated Carbon-Based Hydrogels

This study investigates the physical and electrical properties of the polyvinyl alcohol (PVA) hydrogel incorporated with edible Activated Carbon (AC). Three samples, namely PVA, PVA/AC 0.5, and PVA/AC 1.0 were prepared using the freeze-thaw method. The samples underwent six freeze-thaw cycles, each consisting of freezing at –25°C for 20 hours and subsequent exposure to room temperature for 4 hours. The porous network of hydrogel is attributed to the hydroxyl groups of PVA, resulting from the intermolecular cross-linking of PVA chains. The edible AC was uniformly dispersed within the hydrogel network, leading to a reduction in hydrogel pores. As a result, the electrical resistivity of PVA, PVA/AC 0.5, and PVA/AC 1.0 hydrogels measured 1052.9 ± 165.0 Ω.cm, 403.1 ± 29.2 Ω.cm, and 59.9 ± 4.7 Ω.cm, respectively. The incorporation of edible AC significantly decreased the resistivity of the hydrogel. So, this hydrogel is promising for biomedical and edible electronics applications.

Interplay of Spatial and Topological Defects in Polymer Networks.

Polymer networks are widely used in applications, and the formation of a network and its gel point can be predicted. However, the effects of spatial and topological heterogeneity on the resulting network structure and ultimately the mechanical properties, are less understood. To address this challenge, we generate in silico random networks of cross-linked polymer chains with controlled spatial and topological defects. While all fully reacted networks investigated in this study have the same number of end-functionalized polymer strands and cross-linkers, we vary the degree of spatial and topological heterogeneities systematically. We find that spatially heterogeneous cross-linker distributions result in a reduction in the network's primary loops with increased spatial heterogeneity, the opposite trend as observed in homogeneous networks. By performing molecular dynamics simulations, we investigated the mechanical properties of the networks. Even though spatially heterogeneous networks have more elastically active strands and cross-linkers, they break at lower extensions than the homogeneous networks and sustain slightly lower maximum stresses. Their shear moduli are higher, i.e., stiffer, than theoretically predicted, and higher than their homogeneous gel counterparts. Our results highlight that topological loop defects and spatial heterogeneities result in significantly different network structures and, ultimately, different mechanical properties.

Towards effective recycling routes for polypropylene: Influence of a repair additive on flow characteristics and processability

Plastic recycling is a key aspect to achieve effective polymer circularity, especially for polyolefins for which usually the mechanical recycling is considered a downcycling process. This downcycling phenomenon arises from the progressive deterioration of the polymer microstructure during reprocessing, resulting in a gradual loss of processability and properties, ultimately compromising the possibility of using recycled polyolefins for applications with high engineering requirements.In this work, the effects of the thermomechanical degradation on the microstructure of polypropylene (PP) were assessed by subjecting the polymer to multiple extrusion cycles. The objective is investigating the evolution of the molecular weight and of the macromolecular architecture of PP typically occurring in a mechanical recycling process.Furthermore, a commercially available additive capable of restoring the PP molecular weight was introduced, with the purpose of proposing an effective upcycling strategy for achieving recycled PP with enhanced processability. In particular, the effects of the additive were evaluated following two different strategies that simulate pre-consumer or post-consumer mechanical recycling.The obtained results indicated that the introduction of the additive can effectively prevent the decrease of the molecular weight of reprocessed PP, also inducing some melt structuring phenomena associable with the introduction of some long chain branching and/or crosslinking. Finally, it was demonstrated that different macromolecular architectures for recycled PP can be achieved depending on the residence time during the processing in presence of the additive, opening new perspectives towards the possibility of obtaining recycled PP with modulable flow characteristics and, hence, processability.

Mechanically interlocked [c2]daisy chain backbone enabling advanced shape-memory polymeric materials

The incorporation of mechanically interlocked structures into polymer backbones has been shown to confer remarkable functionalities to materials. In this work, a [c2]daisy chain unit based on dibenzo-24-crown-8 is covalently embedded into the backbone of a polymer network, resulting in a synthetic material possessing remarkable shape-memory properties under thermal control. By decoupling the molecular structure into three control groups, we demonstrate the essential role of the [c2]daisy chain crosslinks in driving the shape memory function. The mechanically interlocked topology is found to be an essential element for the increase of glass transition temperature and consequent gain of shape memory function. The supramolecular host-guest interactions within the [c2]daisy chain topology not only ensure robust mechanical strength and good network stability of the polymer, but also impart the shape memory polymer with remarkable shape recovery properties and fatigue resistance ability. The incorporation of the [c2]daisy chain unit as a building block has the potential to lay the groundwork for the development of a wide range of shape-memory polymer materials.

Gelation of acrylic acid with Ag+ and conversion to Ag nanoparticle as potential system for biomedical applications

Silver (Ag) has been used to cross-link poly (acrylic acid) (PAAc) to obtain antibacterial nanocomposite hydrogel for controlled drug delivery systems. Ag+/PAAc composite hydrogel was prepared by free radical aqueous polymerization of acrylic acid (AAc) using potassium persulfate (KPS) as the initiator in the presence of silver nitrate (AgNO3). Sodium borohydride (NaBH4) was used to reduce the Ag ions present within the hydrogel matrix to generate Ag nanoparticles (Ag NPs). Transmission electron microscopy (TEM) characterization of the sample indicated the formation of Ag nanoparticles that distributed uniformly in the PAAc networks. UV–visible spectrophotometry showed an absorption peak at 425 nm that attribute to the well-known surface Plasmon resonance of the Ag bound in NPs. X-ray diffraction (XRD) pattern showed the appearance of some peaks corresponding to the face-centered cubic (f.c.c.) Ag phase. Energy dispersive spectroscopy (EDS) studies revealed that Ag NPs are successfully formed inside the Ag+/PAAc composite hydrogel. The gelation and crosslinking of PAAc chains with Ag+ by strong interactions between Ag cations and polyanions, deprotonated carboxylic groups of PAAc were identified from the Fourier transform infrared (FTIR) spectrogram. Field emission scanning electron microscopy (FESEM) exhibited an interconnected porous structure with an average pore size of about 10 μ for composite hydrogel that can absorb 440 g water/g dried sample. Dried samples were also loaded with amoxicillin and antibiotic release was studied. The antimicrobial activity of the Ag+ and Ag-NPs hydrogels was tested against Staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa and Escherichia coli.

Fabrication and characterization of alginate-zein core–shell microcapsules for controlled release of buckwheat honey

In this study, extrusion method was employed to fabricate alginate-zein core–shell microcapsules loaded with buckwheat honey by dropping alginate and buckwheat honey mixture solution into a 70.0 % zein ethanol solution(v/v) containing 5.0 % CaCl2 solution (wt%). The microcapsules were constructed by two parts: 1) the formation of hydrophilic beads through the crosslinking of alginate chains with Ca2+; 2) the introduction of alginate beads into the aqueous zein ethanol solution which decreased the ethanol concentration, prompting the precipitation of zein and the deposition of zein nanoparticles onto the surfaces of alginate beads. Comparing with the alginate beads, the prepared microcapsules not only possessed better water-holding capacity, but also achieved controlled release of buckwheat honey. Importantly, the microcapsules significantly retained the antioxidant activity of the buckwheat honey. Therefore, this innovative method for fabricating alginate-zein core–shell microcapsules can suggest a promising approach to broaden the application of buckwheat honey in the food field.

Tracking Dynamic Chemical Reactivity Networks with High-Resolution Mass Spectrometry: A Case of Microplastic-Derived Dissolved Organic Carbon.

Chemical degradation testing often involves monitoring the loss of a chemical or the evolution of a single diagnostic product through time. Here, we demonstrate a novel approach to tracing complex degradation networks using mass-spectrometry-based methods and open cheminformatics tools. Ester- and ether-based thermoplastic polyurethane (TPU_Ester and TPU_Ether) microplastics (350 μm) and microplastics-derived dissolved organic carbon (MP-DOC) were photoweathered in a simulated marine environment and subsequently analyzed by liquid chromatography coupled to high-resolution mass spectrometry. We formula-annotated 1342 and 2344 unique features in the MP-DOC of TPU_Ester and TPU_Ether, respectively. From these, we extracted 199 and 568 plausible parent-transformation product pairs via matching of features (a) with complementary increasing and decreasing trends (Spearman's correlation coefficient between normalized intensity and time), (b) spectral similarities of at least three accurate mass MS2 fragments, and (c) at least 3 ppm agreement between the theoretical and measured change in m/z between the parent-transformation product formula. Molecular network analysis revealed that both chain scission and cross-linking reactions occur dynamically rather than degradation proceeding in a monotonic progression to smaller or more oxygenated structures. Network nodes with the highest degree of centrality were tentatively identified using in silico fragmentation and can be prioritized for toxicity screening or other physicochemical properties of interest. This work has important implications for chemical transformation tracking in complex mixtures and may someday enable improved elucidation of environmental transformation rules (i.e., structure-reactivity relationships) and fate modeling.

A novel approach to enhance the ionic conductivity of silver nanoparticles incorporated PVA:NaBr polymer electrolyte films via fast neutron irradiation

This study investigates the unprecedented impact of fast neutron irradiation on the structural, electrical, and morphological properties of solid polymer electrolytes (SPEs). The SPE, a poly (vinylalcohol) (PVA)-sodium bromide (NaBr) based matrix with the incorporation of silver nanoparticles (AgNPs), was prepared via a solution casting method and subjected to various time intervals of fast neutron irradiation. X-ray diffraction (XRD) analysis revealed a distinct trend in the polymer electrolyte sample's amorphous phase, with decreased levels at lower neutron fluence and augmented levels at higher fluences. Fourier transform infrared (FTIR) spectroscopy highlighted plausible interactions leading to chain scission and cross-linking. Optical investgations below 300 nm exhibited increased absorbance and a shifted position of the surface plasmon resonance peak correlated with AgNPs. Validation of structural changes in the Ag-incorporated PVA-NaBr system was supported by reduced bandgap and elevation in Urbach energy, corroborating FTIR findings. Enhanced thermal stability was confirmed using thermogravimetric (TGA) analysis. Morphological modification upon irradiation were evident via Field emission scanning electron microscope (FESEM). Transport properties evaluated by Nyquist plot fitting showcased escalating room temperature conductivity with neutron fluence, and the highest conductivity obtained was 4.38 × 10−3 S/cm, an order higher than the pristine sample. Transference number measurements (TNM) indicated that the primary charge carriers are ions rather than electrons. This novel approach confirms that neutron irradiation can be used as a potential way to obtain highly conductive polymer electrolyte films.

Optical and Color Modification in Polycarbonate/Polybutylene Terephthalate/Zinc sulfide-Nickel Oxide Nanocomposite Films due to Gamma Irradiation

Nanocomposites (NC) of amorphous polycarbonate (PC), semicrystalline polybutylene terephthalate (PBT), zinc sulfide (ZnS) and nickel oxide (NiO) nanoparticles (NP) were synthesized. We believe that this study is novel in the area of the effect of γ radiation on such NC. Both the synthesized NiO and ZnS had a nanonature of average particle size 4 and 18 nm, respectively, as indicated from the Rietveld refinement of the XRD records. Samples of the PC-PBT/ZnS-NiO NC films were irradiated with several γ doses (10–140 J/cm2). The resultant outcome of the γ irradiation on the optical behavior of the NC films was studied applying ultraviolet spectroscopy (UVs). Upon raising the dose up to 140 kGy, the direct bandgap decreased from 4.11 to 3.6 eV. The Urbach energy showed an opposite tendency; it increased from 0.61 to 0.95 eV. We attribute this to the dominance of chain crosslinks. Also, the optical dielectric loss (ε″) aided in detecting the nature of the microelectronic transitions. It was found that the PC-PBT/ZnS-NiO NC films had direct allowed transitions. Additionally, the γ induced alterations in the dielectric parameters and optical conductivity were studied. Moreover, the optical color changes between the pristine and the irradiated films were assessed. The pristine NC film was uncolored. It showed significant color alterations when irradiated with γ radiation up to 140 kGy. The induced enhancements in the optical properties suggest that the γ radiation is an effective means that allows the use of PC-PBT/ZnS-NiO NC in optoelectronic devices.

Influence of Ionic Conductivity in Polymer Dispersed Antiferroelectric Liquid Crystals (PDAFLC): A Comparison of Critical Fields

Theoretically critical unwinding field was studied using Landau free energy model of three different geometrical configuration of antiferroelectric liquid crystals. In this study, we considered the influence of ionic conductivity both in pure antiferroelectric liquid crystals and polymer dispersed antiferroelectric liquid crystals. We observed that the modified elastic constant which accounted for the interaction of ionic conductivity and polymer cross-linked chains is very much responsible for the variation of critical field.

Impact of annealing temperature on optical, morphological, and surface characteristics of PC/PBT blend exposed to alpha particles

The induced modifications of the optical and surface characteristics in the annealed α-irradiated polycarbonate/polybutylene terephthalate (PC/PBT) blend have been studied in the temperature annealing range from 100 to 200 °C for 15 min. Several techniques have been used to study the changes in chemical composition, optical-electronic transitions, photoemission, contact angle, surface roughness, and hardness of annealed samples comparable to the pristine one. The FTIR spectra exhibit aggregate changes in the band intensities after annealing, indicating the scission and cross-linking of the polymer chains. The intensity of the peaks reduced with α-irradiation but began to increase with increasing annealing temperature. The trend of the function groups found in the annealed samples with the rise in annealing temperature supports the crosslinking mechanism. The UV/Vis spectra revealed that the absorption edges of annealed samples were shifted toward lower photon energy (red shift), reflecting the decrease of optical energy gap from 4 eV to 3.6 eV for direct transition and from 3.8 eV to 3.5 eV for indirect transition at the highest temperature. Further, the number of carbon atoms and the number of carbon clusters increases with the increase in the annealing temperature. The refractive index of the samples decreases from 1.5479 for the pristine sample to 1.4008 for the sample at the highest temperature. Moreover, the dielectric parameters and optical conductivity of the annealed samples were modified after thermal annealing. The PL emission yields are decreased with the increase in annealing temperatures that indicating an enhancement in the non-radiative recombination rate relative to the radiative recombination, which may be due to the increasing in the surface density states. The α-irradiated samples showed a notable increase in contact angle and a notable decrease in surface tension values with increasing the annealing temperatures. The side chain induction, which readily bundles and recombines the annealed parts by raising temperatures, also causes the surface roughness of annealed samples to decrease from 1.099 μm for the pristine sample to 0.696 μm for the annealed sample at the highest temperature. It is noteworthy that there is an increase in the hardness from 10.49 ΜPa for the pristine sample to 41.98 ΜPa for the annealed sample at the highest temperature. This is related to the results of changes in the polymer chains due to the active sites or branching points created by scission, which can lead to cross-linking.

Effects of Drug Conjugation on the Biological Activity of Single-Chain Nanoparticles.

The field of single-chain nanoparticles (SCNPs) continues to mature, and an increasing range of reports have emerged that explore the application of these small nanoparticles. A key application for SCNPs is in the field of drug delivery, and recent work suggests that SCNPs can be readily internalized by cells. However, limited attention has been directed to the delivery of small-molecule drugs using SCNPs. Moreover, studies on the physicochemical effects of drug loading on SCNP performance is so far missing, despite the accepted view that such small nanoparticles should be significantly affected by the drug loading content. To address this gap, we prepared a library of SCNPs bearing different amounts of a covalently conjugated therapeutic drug-sulfasalazine (SSZ). We evaluated the impact of the conjugated drug loading on both the synthesis and biological activity of SCNPs on pancreatic cancer cells (AsPC-1). Our results reveal that covalent drug conjugation to the side chains of the SCNP polymer precursor interferes with chain collapse and cross-linking, which demands optimization of reaction conditions to reach high degrees of cross-linking efficiencies. Small-angle neutron scattering and diffusion-ordered spectroscopy nuclear magnetic resonance (DOSY NMR) analyses reveal that SCNPs with a higher drug loading display larger sizes and looser structures, as well as increased hydrophobicity associated with a higher SSZ content. Increased SSZ loading led to reduced cellular uptake when assessed in vitro, whereby SCNP aggregation on the surface of AsPC-1 cells led to reduced toxicity. This work highlights the effects of drug loading on the drug delivery efficiency and biological behavior of SCNPs.

Correlation of structure, rheological, thermal, mechanical, and optical properties in Low Density Polyethylene/Linear Low Density Polyethylene blends in the presence of recycled Low Density Polyethylene and Linear Low Density Polyethylene

AbstractPost‐industrial low‐density and linear low‐density polyethylene blown films are mechanically recycled for reutilizing in the production of blown films for packaging applications. This process enables the production of films with lower cost and similar properties while preserving the environment and lowering the amount of waste material disposed of. The mechanical recycling process results in the production of recycled pellets. This process includes chopping, washing, drying, and reprocessing. Mixtures of these recycled materials and their virgin form with various concentrations are shaped into blown films with inherent 70 and 30 wt% loadings for low‐density polyethylene and linear low‐density polyethylene components, respectively. Fourier transform infrared spectroscopy results of the recycled material show no contamination or chemical reaction with other materials. Gel permeation chromatography is carried out on the virgin and recycled low‐density polyethylene and linear low‐density polyethylene, and the results indicate the occurrence of chain session and crosslinking during the recycling process. The decline in the thermal properties of the samples, seen from the differential scanning calorimetry results, indicates the presence of crosslinks. The effect of structural changes caused by the recycling process on the rheological properties is studied. The miscibility of the blend components is evaluated by Cole–Cole plots and then further proved by Han and Van Gurp–Palman curves. Mechanical properties display an upturn following the presence of the crosslinkes. A decline in the optical properties in the films caused by the refraction of light by the crosslink structure in the film bulk and on the surface is evident.Highlights LDPE and LLDPE were recycled according to the circular economy approach Blown films containing virgin and recycled LDPE and LLDPE were produced Chain scission and crosslinking as a result of recycling were studied Rheological, thermal, mechanical, and optical properties were studied

Structural Insights into a Side Chain Cross-Linking Biarylitide P450 from RiPP Biosynthesis

Structural Insights into a Side Chain Cross-Linking Biarylitide P450 from RiPP Biosynthesis

Hydrogen bonding regulation on phase change in stimuli responsive copolymer aqueous solution

Hydrogen bonding (HB) is vital for the phase transition and physical properties of stimuli responsive copolymers. However, the governing mechanism remains unclear. Herein, we investigated the HB dynamics in a representative thermo-responsive copolymer (PNIPAM-AM) aqueous solution. Three types of HB were identified: polymer-polymer chain (CO:H–N), polymer chain-water molecule (CO:H–O) and water-water molecules (H–O:H–O) by vibrational spectroscopy. Increasing polymer concentration, the H–O:H–O softened and CO:H–O stiffened, leading to the destruction of HB network in water-water clusters. Upon increasing solution temperature, CO:H–O softened while CO:H–N stiffened, resolving the dehydration and cross-linking of polymer chains. Confinement of water molecules in the “cages” (∼ tens to hundreds of micrometers) after sol-gel phase transition was visualized, disclosing the mechanism of water holding capacity of PNIPAM-AM. The correlation of molecule vibration and copolymer microscopic structure was established, contributing to the fundamental understanding of phase behavior and physical properties regulations in stimuli responsive copolymer aqueous solution.