Differential Scanning Calorimetry Results Research Articles

Thermodynamics of Tri- and Tetraepoxyimidazolium NTf2 Amine Polyaddition: A Theoretical Perspective.

The thermodynamics of newly designed tri- and tetraepoxyimidazolium NTf2 monomers reacting with several diamines used as curing agents to form epoxy/amine thermosets was studied. The ability of each epoxy/amine combination to induce cross-linking both through the substitution of multiple epoxy groups and through multiple additions to a single amine was investigated. Through an increased understanding of the thermodynamics of epoxy-amine polymerization in complex polyepoxy-ILs, it is possible to more thoroughly understand the factors affecting the reactivity in these complex systems. These calculations showed that while each possible epoxy-amine combination was exergonic to both forms of cross-linking, the degree to which both amines-induced cross-linking and epoxy-induced cross-linking was favored varied between epoxy-amine combinations. Thermodynamic results obtained using density functional theory were experimentally validated through differential scanning calorimetry results, wherein similar trends were noted between theory and experiment. Among the trends noted in amines-epoxy combinations tested, tetraepoxyimidazolium NTf2/PACM (i.e., a cycloaliphatic diamine) was found to be a prime candidate for amine cross-linking, with the addition of a second epoxy to a single amine group being notably the most negative of all epoxy-amine combinations at -77.6 kJ mol-1. While in the case of epoxy cross-linking, the aliphatic polyetheramine denoted Jeffamine-D230-containing systems were found to be the most exergonic, with additions of primary amines to triepoxyimidazolium and tetraepoxyimidazolium NTf2 averaging -86.9 kJ mol-1. Interaction energy analysis indicated that the aromatic amine named sulfanilamide is the most favorable to engage in reactions due to having the most negative interaction energies with already highly substituted epoxy monomers. These results can be used to adjust the cross-linking possibilities of tri- and tetraepoxyimidazolium NTf2/amine polymerization and give insight into the predominant cross-linking reactions in these unique systems.

Assessment of Unfrozen Water Content in Copper Bentonites Using the 1H NMR Technique: Optimization, the Method's Limitation, and Comparative Analysis with DSC.

Studies on changes in unfrozen water content in copper bentonite from Slovakia were conducted using both differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) methods. The aims of this study were to 1. optimize the method for determining changes in unfrozen water content using the 1H NMR technique in model bentonites based on the DSC results; 2. analyze the relationship between unfrozen water content, as determined via DSC and the optimized NMR technique, and the physicochemical parameters of bentonites; and 3. identify the limitations in determining changes in unfrozen water content using the 1H NMR technique in relation to copper-contaminated bentonites. The results obtained using the optimized NMR method applied to the model bentonites correlated well with the DSC results. The unfrozen water content in the Cu-contaminated bentonites was 2-18% lower after NMR compared to the DSC results, likely due to the mobility of copper ions and their paramagnetic properties. Statistically significant differences in unfrozen water content between the DSC and NMR methods were observed, depending on molar concentration, copper ion concentration, and temperature, confirmed via Analysis of Variance (ANOVA). Calorimetric studies are recommended for investigating unfrozen water content changes in contaminated clays. Further NMR research could identify metals influencing free induction decay signals under varying physicochemical conditions.

Nanosponges-based Drug Delivery System for the Cosmeceutical Applications of Stabilized Ascorbic Acid.

L-Ascorbic acid (AA) is a highly unstable compound, thus, limiting its use in pharmaceutical and cosmetic products, particularly at higher concentrations. This study aimed to stabilize the highly sensitive molecule (AA) by encapsulating it in β- cyclodextrin nanosponges (β-CD NS) that can be used further in preparing cosmeceuticals products with higher AA concentrations and enhanced stability. The NS has been synthesized by the melting method. The AA was encapsulated in β-CD NS by the freeze-drying process. The prepared NS were characterized by FTIR spectrometry, SEM, Atomic Force Microscopy (AFM), zeta sizer, Differential Scanning Calorimetry (DSC), and the physical flow characteristics were also studied. The in vitro drug release was carried out on the Franz apparatus using a combination of two methods: sample & separate and dialysis membrane. The assay was performed using a validated spectrometric method. The entrapment efficiency of AA in β-CD NS indicated a good loading capacity (83.57±6.35%). The FTIR, SEM, AFM, and DSC results confirmed the encapsulation of AA in β-CD NS. The particle size, polydispersity index, and zeta potential results ascertained the formation of stabilized monodisperse nanoparticles. The physical flow characteristics showed good flow properties. Around 84% AA has been released from the NS in 4 h following the Korsmeyer-Peppas model. The AA-loaded NS remained stable for nine months when stored at 30±2°C/65±5% RH. It is concluded that the prepared NS can protect the highly sensitive AA from degradation and provide an extended-release of the vitamin. The prepared AA-loaded β-CD NS can be used to formulate other cosmeceutical dosage forms with better stability and effect.

Preparation and Evaluation of Aceclofenac Solid Dispersion by Fusion Technique and Effervescent Assisted Fusion Technique: Comparative Study

Solid dispersion (SD) is one of the most widely used methods to resolve issues accompanied by poorly soluble drugs. The present study was carried out to enhance the solubility and dissolution rate of Aceclofenac (ACE), a BCS class II drug with pH-dependent solubility, by the SD method. Effervescent assisted fusion technique (EFSD) using different hydrophilic carriers (mannitol, urea, Soluplus®, poloxamer 188, and poloxamer 407) in the presence of an effervescent base (sodium bicarbonate and citric acid) in different drug: carrier: effervescent base ratio and the conventional fusion technique (FSD) were used to prepare ACE SD. Solubility, dissolution rate, Fourier transformation infrared spectroscopy (FTIR), PowderX-ray diffraction study (PXRD), and Differential scanning calorimetry (DSC) were determined for the SD obtained from both techniques as a comparative study. The results showed that EFSD using ACE: Soluplus®: effervescent base in a ratio of 1:2:1 had higher solubility and dissolution rate than that obtained from FSD prepared by ACE: Soluplus® in a ratio of 1:2. However, the two techniques obtained the amorphous form according to XRD and DSC results. It can be concluded that EFSD is a promising method for the solubility and dissolution rate improvement of BCS class II drugs.

Utilization of marine and agro-waste materials as an economical and active food packaging: Antimicrobial, mechanical and biodegradation studies of O-Carboxymethyl chitosan/pectin/neem composite films

The present work deals with the eco-friendly preparation of highly degradable food packaging films consisting of O-CMC (O-Carboxymethyl Chitosan) and pectin, incorporated with neem (Azadirachta indica) leaves powder and extract. This study aimed to investigate the tensile properties, antimicrobial activity, biodegradability, and thermal behavior of the composite films. The results of tensile strength and elongation at break, showed that the incorporation of neem leaves powder improved the tensile properties (7.11 MPa) of the composite films compared to the neat O-CMC and pectin films (3.02 MPa). The antimicrobial activity of the films was evaluated against a panel of microorganisms including both gram-positive and gram-negative bacteria as well as fungi. The composite films exhibited excellent antimicrobial activity with a zone of inhibition (12–17.6 mm) against the tested microorganisms. The opacity of the composite films ranges from 1.14 to 4.40 mm−1 and the addition of fiber causes a decrease in opacity value. Biodegradability studies were conducted by Soil burial method and the films demonstrated complete biodegradability within 75 days. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) of composite films show that they are thermally stable and might be used in food packaging.

Effect size of carbon micro-nanoparticles on cyclic stability and thermal performance of Na2SO4⋅10H2O–Na2HPO4⋅12H2O phase change materials

In this paper, carbon particles with micro- and nano-particle size were synthesized through a hydrothermal reaction of glucose, namely C-1(123.1 nm), C-2(229.2 nm), C-3(335.1 nm), C-4(456.2 nm) and C-5(534.0 nm) with distinct sizes. We utilized five size carbon particles as individual fillers into the EHS matrix materials to prepare composite eutectic phase change materials (C/EHS PCMs) by melt blending technique. The impact of carbon particle size on the dispersion stability and thermal properties of Na2SO4⋅10H2O–Na2HPO4⋅12H2O (EHS) phase change materials was investigated. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) analysis were done to analyze the diameters of carbon particles. The cryogenic-scanning electron microscopy (Cryo-SEM) analysis indicated that the carbon particles resulted in modification in the morphology of the EHS. The results of in situ X-ray diffraction (XRD) and Fourier-transformed infrared (FTIR) analysis showed only simple physical mixing between carbon particles and EHS. It is shown that adding 0.2 wt.% C-2 can decrease the supercooling degree of EHS to 1.5[Formula: see text]C. The cyclic stability of C/EHS varies significantly depending on the size of carbon particles. The thermal conductivity of EHS increased by 42.1%, 39.9%, 14.4%, 19.5%, and 18.8% with the addition of C-1, C-2, C-3, C-4, and C-5, respectively, at a mass fraction of 0.2%. The results of differential scanning calorimetry reveal that the incorporation of C-1, C-2, C-3, and C-4 into EHS leads to an enhancement of latent heat. The latent heat capacity of EHS with 0.2 wt.% C-2 is 243.4 J⋅g[Formula: see text], and after undergoing 500 cycles of solid-liquid phase transition, the latent heat remained above 200 J⋅g[Formula: see text]. Through the comprehensive analysis, the C-2/EHS composite phase change material holds significant potential for advancing building insulation and solar energy storage technologies.

Multifunctional, robust, and self‐healable polyurethane coatings cross‐linked by Diels–Alder reaction of calix[4] arenes containing furan groups

AbstractSelf‐healing coatings can restore their performance after inevitable damage and are promising in the industry owing to their longer service life and lower repair cost. The use of Diels–Alder reaction bonds is well‐known to generate thermally self‐healing coatings. In this study, a series of cross‐linked self‐healing polyurethane (PU) coatings were synthesized through Diels–Alder reactions of p‐tert‐butyl calix[4]arene bearing furan groups (C4A‐FA) as a new chain extender and a bismaleimide (BMI) polyether amine as a Diels–Alder cross‐linking agent. Adding C4A‐FA to PUs improves their mechanical properties, thermal stability, and self‐healing ability. Additionally, these modifications can result in the formation of composite networks with PU that exhibit thermoreversibility and self‐healing properties. These changes have led to PUs containing modified calix[4]arene (C4A‐FA) having better properties compared with unmodified calix[4]arene PUs. The properties of prepared coatings were evaluated by Fourier transform infrared spectroscopy, scanning electron microscope, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), and tensile tests compared with a typical PU sample. The tensile and TGA results show an improvement in the thermal and mechanical properties of the polymers by increasing the C4A‐FA content. By replacing 15% of butandiol (BDO) with C4A‐FA in PU pure, the tensile strength increased from 1.69 to 5.14 MPa. Furthermore, adding diels–alder (DA) bonds enhanced the tensile strength to 10.49 MPa for PU‐C4A15‐DA. According to DSC results, a broad endothermic peak from nearly 80–140°C confirmed the retro‐DA reactions in the synthesized thermoreversible samples. The healing efficiency of the PU‐C4A15‐DA sample was obtained at 92.5% (measured by tensile test), which is the highest value among cross‐linked self‐healing PUs reported in the literature.

New Insights into the Chemical Compatibility of Nitrochitosan with Potential Energetic Molecules

This study provides new insights into the compatibility of a promising energetic polysaccharide, called nitrochitosan (NCS), with energy-rich ammonium perchlorate (AP), ammonium nitrate (AN), and hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO) molecules, in order to survey their application prospects in solid rocket propellants and explosives. For this purpose, differential scanning calorimetry (DSC) and thermogravimetric (TGA) analyses were carried out to accurately evaluate the chemical compatibility of NCS with the selected energetic molecules following the STANAG 4147 criterion. Fourier transform infrared spectroscopy (FTIR), as a non-thermal complementary technique, was also performed to further elucidate the eventual structural alterations occurring in the physical mixtures (NCS/AP, NCS/AN, and NCS/HNTO). Based on DSC results, the maximum exothermic peak temperature difference between NCS (Tpeak = 164.7 °C) and the as-prepared NCS/AP (Tpeak = 164.3 °C), NCS/AN (Tpeak = 204.3 °C), and NCS/HNTO (Tpeak = 197.0 °C) admixtures is found to be lower than 4 °C. Moreover, TGA experiments showed that the observed mass losses of the physical mixtures are lower than the sum of the weight losses of their respective individual compounds. Therefore, thermal results demonstrated the excellent chemical compatibility of NCS with the corresponding energetic molecules. In addition, FTIR measurements highlighted the absence of chemical interactions between NCS and the selected AP, AN, and HNTO. Therefore, a deep investigation into the characteristics of such energetic composites and their real-world applications will be among the main focuses of the postulated next stage of research.

Differential scanning calorimetry as a tool to assess the oxidation state of cold-pressed oils during shelf-life

AbstractCold-pressed oils are highly prone to the peroxidation process, which causes a rapid decline in quality. Thus, there is a need to develop instrumental methods instead of conventional chemical analysis consuming large quantities of harmful chemicals. Differential scanning calorimetry (DSC) is a valuable analytical tool for assessing the oxidative stability of oils. Cold-pressed flaxseed, camelina and hemp seed oils from different cultivars, which had been stored for six months in room conditions under natural light exposure, were tested. Chemical methods for measuring changes in oxidative stability during storage of oils included determination of peroxide value (PV), p-Anisidine value (p-AV), total oxidation value (TOTOX) value and acid value (AV). Parameters like oxidation induction time (OIT) in isothermal mode (120, 140 °C) and onset temperature (Ton) in non-isothermal mode (heating rate 2, 5 °C/min) were established from DSC curves. Data for OIT and Ton plotted against time showed a strong, significant (p ≤ 0.05) descending trend for all oils. However, flaxseed and hempseed oils revealed a more rapid deterioration during storage compared to camelina seed oils. All DSC results showed promising repeatability of the oxidative characteristics for three types of cold-pressed oils, regardless of their origins in different cultivars. However, the most suitable for monitoring the deteriorative changes in oils during storage was the isothermal test carried out at a temperature of 120 °C, for which the correlations with chemical indicators (PV, p-AV, TOTOX) were highly significant (p ≤ 0.0001). Linear discriminant analysis (LDA) based on the DSC results revealed, that the first discriminating function significantly separated the fresh oils from stored oils. The study showed that, based on a starting point defined for fresh oils, the DSC technique can be used to effectively and ecologically monitor the deterioration of oils by oxidation, instead of harmful chemical analyses.

Synthesis, polymerization and thermal properties of bio‐based benzoxazine resins containing imide or amide functionality

AbstractTwo novel bio‐based benzoxazine monomers containing imide or amide group (HPIDD‐fa and HPBA‐fa) were synthesized from raw materials of benzoyl chloride/phthalic anhydride, tyramine, furfurylamine and paraformaldehyde via a two‐step reaction. Fourier transform infrared spectroscopy (FT‐IR), proton and carbon nuclear magnetic resonance (NMR) spectroscopies were performed to characterize the structures of the benzoxazine monomers. The curing behavior was investigated by using differential scanning calorimetry (DSC) and in situ FT‐IR, and the DSC results indicate that the peak curing temperatures of HPIDD‐fa and HPBA‐fa are centered at 248.5 and 230.1°C, respectively. In addition, thermogravimetric analysis (TGA) suggests that the newly developed bio‐based benzoxazine‐derived polybenzoxazines present excellent thermal stability with Td10 (temperature at 10% weight loss) of 385 and 368°C for poly(HPIDD‐fa) and poly(HPBA‐fa), respectively. The current investigation suggests that our newly obtained bio‐based thermosetting resins are promising materials for high‐tech applications.

Flavonoid-incorporated starch and poly(vinyl alcohol) film: Sensitive and selective colorimetric sensor for copper identification and quantification in beverages and environmental samples

Colorimetric sensors based on an eco-friendly sensor molecule immobilized into a polymer matrix have broad applications for detecting trace elements. However, their potential for quantitative analysis of these elements remains little explored. Here, we incorporated rutin or quercetin into films based on starch, poly(vinyl alcohol), and glycerol to detect and quantify Cu2+ in different matrices. The films were characterized by colorimetric assays, thickness, and solubility analyses, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and mechanical assays. Incorporating the flavonoids in the film decreased its solubility, tensile strength, and modulus of elasticity, while increased its cross-sectional surface irregularity. XRD and DSC results indicated an increase in film crystallinity in the presence of rutin or quercetin. FTIR analyses showed a more effective incorporation of quercetin than rutin in the polymeric matrix, which was confirmed by flavonoid release studies from the film. The film containing quercetin exhibited selectivity in identifying copper in liquid matrices, changing its color from light yellow to dark yellow. An analytical method to quantify Cu2+ was developed, presenting a linear response range of 0.20–1.20 mg L−1, with detection and quantification limits of 0.060 and 0.20 mg L−1, respectively, very lower than other methods based on polymeric matrices containing natural dyes. The method was successfully applied for Cu2+ determination in cachaça and tap water samples, achieving high accuracy (96–104% of recovery) and precision (relative standard deviation < 6.7%). Our findings represent an advancement in the field of sensors based on natural dyes, demonstrating that such sensors can achieve high sensitivity without the need for complex sample preparation methods.

Preparation, characterization, and life cycle assessment of banana rachis-recycled high-density polyethylene composites

Agro-industrial wastes are sustainable resources that have advantages as a reinforcement for polymeric matrices. This study examined the use of banana rachis fiber (BRF) in reinforcing the recycled high-density polyethylene (rHDPE) matrix. For this purpose, polymer composites with 5–20 wt% of BRF were prepared by the extrusion process using a twin-screw extruder and followed a hot press method. The structure of rHDPE/BRF composites and their characteristic peaks of degradation were successfully identified by the Fourier-transformed infrared spectroscopy and thermogravimetric analysis techniques, respectively, revealing a good dispersion of BRF in rHDPE. Differential scanning calorimetry results of the composites demonstrated that melt enthalpy decreases as the amount of BRF increases. XRD diffractograms revealed a crystallinity reduction of rHDPE due to the increase of fiber within the polymer matrix, which is reflected in the characteristic peaks' intensity decrease of HDPE. Variation in thermal and chemical properties with the addition of BRF in rHDPE was successfully evaluated in this study. Life cycle assessment for 1 kg composite production has also been evaluated. The banana rachis-rHDPE composite materials reduce the overall environmental impacts when the filler concentration increases.

Effects of Electron Irradiation and Temperature on Mechanical Properties of Polyimide Film.

Polyimide (PI) is widely deployed in space missions due to its good radiation resistance and durability. The influences from radiation and harsh temperatures should be carefully evaluated during the long-term service life. In the current work, the coupled thermal and radiation effects on the mechanical properties of PI samples were quantitatively investigated via experiments. At first, various PI specimens were prepared, and electron irradiation tests were conducted with different fluences. Then, both uniaxial tensile tests at room temperature and the dynamic mechanical analysis at varied temperatures of PI specimens with and without electron irradiation were performed. After that, uniaxial tensile tests at low and high temperatures were performed. The fracture surface of the PI film was observed using a scanning electron microscope, and its surface topography was measured using atomic force microscopy. In the meantime, the Fourier-transform infrared spectrum tests were conducted to check for chemical changes. In conclusion, the tensile tests showed that electron irradiation has a negligible effect during the linear stretching period but significantly impacts the hardening stage and elongation at break. Moreover, electron irradiation slightly influences the thermal properties of PI according to the differential scanning calorimetry results. However, both high and low temperatures dramatically affect the elastic modulus and elongation at break of PI.

Effectiveness of modified lignin on poly(butylene adipate‐co‐terephthalate)/poly(lactic acid) mulch film performance

AbstractIn this work, the biodegradable poly(butylene adipate‐co‐terephthalate) (PBAT)/poly(lactic acid) (PLA) blend (ECOVIO®) and lignin, a renewable and biodegradable natural polymer with high UV absorption and modified by gamma radiation were used to produce agriculture mulch films. Lignin was gamma‐irradiated at 30 and 60 kGy. The irradiated and non‐irradiated lignin content of 2 wt% was incorporated into PBAT/PLA blend matrix using a twin‐screw extruder and extrusion blown film to prepare flexible films. PBAT/PLA/LIGNIN films were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), x‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), tensile tests, contact angle, and UV–Vis analysis. FTIR spectra showed partial miscibility between PBAT/PLA and lignin, being intensified in irradiated lignin compounds. The DSC and XRD results confirmed that the degree of crystallinity of the blends was not significantly influenced by lignin addition. FE‐SEM images showed better dispersion and miscibility in PBAT/PLA/Irradiated lignin. Miscibility improvement provided by irradiated lignin promoted better mechanical properties, mainly with lignin irradiated at 60 kGy. PBAT/PLA/LIGNIN films containing 2 wt% showed excellent UV‐barrier property and greater hydrophobicity. Summing up, incorporation of low contents of irradiated lignin could be an interesting alternative to produce biodegradable UV‐blocking agriculture mulch films.

Development of nanomodified eco-friendly thermal energy storing cementitious composite using PCM microencapsulated in biosourced encapsulation shell

This study presents the development of a thermal energy storing cementitious composite that incorporates phase change material (PCM) microencapsulated in biosourced polymer shell (m-PCM). The biodegradability of the encapsulated PCM was assessed using Nuclear Magnetic Resonance (NMR), which confirmed the high biodegradability of the m-PCM shell under specific environmental conditions. To examine the thermophysical properties of the m-PCM, Differential Scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA) were performed. The DSC results revealed exothermic enthalpies of 84.7 J/g and 140.2 J/g, with associated peak temperatures of − 3.2 °C and − 22.9 °C, respectively. Subsequently, the m-PCM was incorporated into cement-based mortar at proportions of 5%, 10%, and 15% by weight of binder. Uniaxial compression tests were conducted to evaluate the effect of the m-PCM on the mechanical properties of the mortar. The results indicated a significant decrease in mechanical strength upon incorporating the m-PCM. However, this reduction in strength was mitigated by the addition of silica fume (SF) and multiwalled carbon nanotubes (MWCNTs) in combination. Furthermore, a thermal cycling test was performed to examine the behavior of the nanomodified m-PCM incorporated mortar under varying ambient conditions. The results showed that the addition of MWCNTs improved both the mechanical performance and thermal performance of the composite.

Effect of post-heat-treatment on thermal and physical characteristics of NiTi tubes produced via conventional drawing and laser powder bed fusion

NiTi is one the metal alloys exhibiting shape memory and superelasticity which makes it suitable for a wide range of engineering and biomedical applications. Nickel-rich NiTi requires heat treatment and cold work as post-processing steps to enable appropriate phase production for final applications. In the current work, NiTi tubes (50.8%Ni-49.2%Ti) produced using Laser Powder Bed Fusion (PBF-LB) and conventional drawing were heat treated at a constant temperature of 500 °C for 10, 30, and 60 min. Differential scanning calorimetry results indicate that the austenite finish temperatures for the tubes were set at 25.4 °C and 26.62 °C after 60 min of heat treatment for the PBF-LB and conventionally drawn tubes respectively. The enthalpy of phase transformation for PBF-LB tubes increased from 2.89 J/g to 17.14 J/g while for conventionally drawn tubes it increased from 5.41 J/g to 16.08 J/g. The EDX measurements on as-built and heat-treated tubes indicated no loss of nickel during the heat-treatment process. The thermal expansion results show an unstable evolution of CTEs in as-built NiTi tubes which were stabilized via heat-treated with resulting CTE ≈11.4 × 10−6/ºC. The hardness decreased in the heat-treated tubes as compared to the as-built tubes. The hardness decreased by 12.6% for PBF-LB and 12.4% for the conventionally drawn tubes respectively.

Preparation of polybenzoxazine/resorcinarene composites with low dielectric constants

AbstractA series of polybenzoxazine (PBZ)/resorcinarene composites with low dielectric constants were prepared by the thermal curing of a siloxane‐containing benzoxazine (P‐aptmds) with C‐methylcalix[4]resorcinarene (CMCR). CMCR with active hydroxyl groups could serve to lower the thermal curing temperature of P‐aptmds. The results of differential scanning calorimetry (DSC) showed that the peak exothermic temperature of P‐aptmds decreased from 262°C to 192°C. The introduction of CMCR increased the crosslinking density of the PBZ/CMCR composites and improved the thermal properties. Due to the incorporation of CMCR with macrocyclic structure, the dielectric constant and the dielectric loss of the PBZ/CMCR composite could be reduced to 2.63 and 0.0055 at 1 MHz, respectively. Moreover, the PBZ/CMCR composites possessed good hydrophobicity and low water absorption. This approach was expected to provide a facile design strategy of low dielectric composite materials.

Synthesis of acetone-fractionated hardwood kraft lignin-based adhesive crosslinked with epichlorohydrin

Studies on lignin have garnered great interest for increasing the value of lignin-added products, especially lignin-based adhesives. However, even with the advantage of abundant aromatic materials in lignin, its aromaticity and heterogeneity require its fractionation with various solvents. This study used hardwood kraft lignin (HKL) extracted from black liquor and was acetone-fractionated to produce acetone-soluble HKL (AS-HKL) and acetone-insoluble HKL (AI-HKL). The lignins were crosslinked with different amounts of epichlorohydrin (ECH; 5%, 10%, and 15%) for the synthesis of lignin-based adhesives with a three-dimensional network. The crosslinked HKLs were characterized with gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), nuclear magnetic resonance (13C-NMR), and differential scanning calorimetry (DSC) to investigate their molecular weight, chemical structure, and thermal curing behavior. AI-HKL exhibited higher molecular weight than that of AS-HKL. As expected, the FT-IR and 13C-NMR spectra showed successful crosslinking of HKL by ECH with the intensity reduction of − OH, increased C–O stretching, and new peak appearance. From the DSC results, the exothermic peak temperature for crosslinking was 100 °C–130 °C. HKL and AI-HKL plywoods showed good tensile shear strength with minimal variations when they were crosslinked with 10 and 15% ECH. These results suggest the potential of high molecular weight HKL as lignin-based adhesives for wood bonding.

Re-Assemblable, Recyclable, and Self-Healing Epoxy Resin Adhesive Based on Dynamic Boronic Esters.

Thermosetting adhesives are commonly utilized in various applications. However, covalent cross-linked networks prevent thermosetting adhesives from being re-assembled, which necessitates higher machining precision. Additionally, the primary raw materials used in adhesive preparation are derived from non-renewable petroleum resources, which further constrain adhesive development. In this study, a recyclable adhesive was developed by incorporating dynamic boronic esters into epoxy resin derived from soybean oil. The successful synthesis of epoxidized soybean oil and boronic esters was confirmed through the analysis of proton nuclear magnetic resonance spectra and differential scanning calorimetry results. Swelling tests and tensile curves demonstrated the presence of covalently cross-linked networks. Self-healing and reprocessing experiments indicated that the cross-linked network topology could be re-assembled under mild conditions.

A differential scanning calorimetry (DSC) approach for assessing the quality of polyethylene terephthalate (PET) waste for physical recycling: a proof-of-concept study

Physical recycling of plastics is among the most important approaches of circular economy. The efficiency of the recycling is influenced by many factors including the number of recycling cycles, composition of plastics, chemical modifications, additives and others. Currently, however, there are no methods enabling to distinguish the quality of plastics for recycling. In this work, we address this issue and suggest a new method based on the correlation of solely thermophysical properties of polyethylene terephthalate (PET) waste obtained using differential scanning calorimetry (DSC) during repeated heating and cooling. The combination of results of differential scanning calorimetry and advanced statistical methods enabled to separate 76 PET samples into six groups according to their origin, chemical modification, degradation and suitability for recycling. The discriminant analysis enabled to suggest a model which uses for the discrimination a combination of temperatures and enthalpies of melting and crystallization. The approach illustrates that thermophysical properties, which can be obtained using a single DSC experiment, can be used to distinguish the polymers of various origin and quality.