Dynamic Differential Scanning Calorimetry Research Articles

Manufacturing process and annealing influence on the dynamic mechanical properties and physical structure of LLDPE thin films

Thin films of Linear Low-Density Polyethylene are used for stratospheric balloon applications. They undergo tensile mechanical stress on a wide range of temperatures [-95; 55]°C. The aim of this study is to compare the influence of blown film and double-bubble manufacturing processes on the crystalline phase and mechanical properties of the films through their operating temperatures (flight, storage, and transportation temperatures). Dynamic Mechanical Analysis and Differential Scanning Calorimetry have been used to monitor the dynamic mechanical properties in tension mode and the crystalline phase of the films respectively. The films mechanical properties are dependent on their manufacturing process. The double-bubble process allows isotropic tensile mechanical properties regarding stretching direction, whereas the blown film process favors only transversal direction. To simulate different storage conditions, annealing has been performed. The influence of annealing on the tensile mechanical properties of the films depends mainly on the internal stress stored during manufacturing. The double-bubble process produces a biaxially stretched film with a higher stretching ratio than blown films. The dissipated internal stress can be associated with thermal shrinkage and goes up to 10 % for the biaxially stretched film. The more internal stress is stored, the more E′ and E″ increases. Annealing also favors the formation of a secondary crystalline phase that is dependent on annealing temperature and time, and exhibits αc relaxation. After annealing, the amorphous phase is less stretched, and the crystalline phase keeps its orientation.

Modified Cellulose Nanocrystals Enabled Antimicrobial Polymeric Films

AbstractThis study presents an antimicrobial polymeric material comprising cellulose nanocrystals (CNCs) grafted with an antimicrobial oligomer, polyhexamethylene guanidine hydrochloride (PHGH). A one‐pot reaction is implemented to graft PHGH onto CNCs, creating a non‐leaching and nano‐sized antimicrobial additive (mCNC). The mCNC is subsequently incorporated into a model polymer, polylactic acid (PLA), with concentrations of 2.5 to 10 wt.% and tested for its antimicrobial activity during dynamic and static contact with Escherichia coli and Bacillus subtilis bacteria. The grafting of PHGH onto CNC is confirmed with Fourier transform infrared spectroscopy (FTIR), X‐ray spectroscopy (XPS) and elemental analysis. The effect of mCNC incorporation at various loading levels on the morphology and physicomechanical properties of PLA is investigated with polarized optical microscope (POM), scanning electron microscope (SEM), dynamic mechanical analysis (DMA), tensile testing, and differential scanning calorimetry (DSC). In terms of the antimicrobial action, the films exhibited potent efficacy against Gram‐positive bacteria (B. subtilis), with growth inhibition of 3.97 to 4.66‐log reduction. However, 10 wt.% of mCNC loading is needed to achieve a significant bacterial inhibition (>6.24‐log) of the Gram‐negative bacteria (E. coli). Overall, the incorporation of PHGH grafted CNCs in polymers provided a non‐leaching antimicrobial film that has potential application in food packaging.

Nonisocyanate Polyurethane Segmented Copolymers from Bis-Carbonylimidazolides.

Bis-carbonylimidazolide (BCI) functionalization enables an efficient synthetic strategy to generate high molecular weight segmented nonisocyanate polyurethanes (NIPUs). Melt phase polymerization of ED-2003 Jeffamine, 4,4'-methylenebis(cyclohexylamine), and a BCI monomer that mimics a 1,4-butanediol chain extender enables polyether NIPUs that contain varying concentrations of hard segments ranging from 40 to 80wt. %. Dynamic mechanical analysis and differential scanning calorimetry reveal thermal transitions for soft, hard, and mixed phases. Hard segment incorporations between 40 and 60wt. % display up to three distinct phases pertaining to the poly(ethylene glycol) (PEG) soft segment Tg , melting transition, and hard segment Tg , while higher hard segment concentrations prohibit soft segment crystallization, presumably due to restricted molecular mobility from the hard segment. Atomic force microscopy allows for visualization and size determination of nanophase-separated regimes, revealing a nanoscale rod-like assembly of HS. Small-angle X-ray scattering confirms nanophase separation within the NIPU, characterizing both nanoscale amorphous domains and varying degrees of crystallinity. These NIPUs, which are synthesized with BCI monomers, display expected phase separation that is comparable to isocyanate-derived analogues. This work demonstrates nanophase separation in BCI-derived NIPUs and the feasibility of this nonisocyanate synthetic pathway for the preparation of segmented PU copolymers.

Thermomechanical characterisation of reprocessable, siloxane-based, glass-fibre-reinforced vitrimers

Polymer composites have been extensively used for the last 30 years in the automotive, green-energy, maritime and aerospace industries. While the demands of composites' applications are increasing, complications are arising regarding their sustainability. In this work, a siloxane-based vitrimer with fast stress-relaxation, and its Glass-Fibre-Reinforced Vitrimer (GFRV) were manufactured and mechanically characterised as a sustainable alternative to thermoset composites produced by infusion. Dynamic mechanical analysis and differential scanning calorimetry were performed to identify the ageing effect on the glass-transition temperature of the materials. Tensile and in-plane shear tests were executed to investigate the materials’ performance at elevated temperature. The results were compared to the ones of a thermoset benchmark and showed that after ageing and up to 50 °C, both the neat vitrimer and its corresponding composite exhibited a thermomechanical performance comparable to their thermoset counterparts. GFRV specimens were then successfully reprocessed by hot-pressing up to two consecutive cycles. The GFRV specimen was thermoformed into an omega-stiffener profile by the first hot-pressing cycle, while its flat profile was restored during the second cycle. Finally, the reprocessing results were evaluated by optical microscopy, demonstrating that the newly developed advanced GFRV is indeed a viable, sustainable alternative.

Analysis of the thermal properties in short sansevieria cylindrica fibre/PLA composites processed by twin screw extruder followed by hot press molding technique

Abstract Short Sansevieria cylindrica fibre/polylactic acid composites (SCFP) were fabricated using a twin screw extruder followed by the hot press technique, with variations in fibre loadings of 10 wt%, 20 wt%, 30 wt% and 40 wt%. The thermal properties of SCFP were assessed through dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Notably, the samples loaded with 40 wt% of fibre exhibited an increased storage modulus. In terms of loss modulus, the fibre-loaded samples displayed high values, indicating more heat is released during DMA experiment. Interestingly, the composite trend did not solely rely on increasing fibre loading, highlighting the intricate interplay between reinforcement and matrix crucial for determining viscoelastic properties across various temperatures. The TGA results revealed a decrease in inflection temperature with increasing fibre loadings, accompanied by a proportional rise in residues. The DSC thermograms indicated minimal differences in Tg, Tcc, and Tm values among composites with varying fibre loadings. However, neat PLA showed slightly higher values than the composites. On the other hand, reinforcing SCF into the PLA matrix promoted the crystallization of PLA by 1%–3% with the maximum degree of crystallinity of 25.4% obtained for 30 wt% of SCFP.

Comparison between cure kinetics by means of dynamic rheology and DSC of formaldehyde-based wood adhesives

ABSTRACT Comparative analysis of the chemical and rheological curing kinetics of formaldehyde-based wood adhesives is crucial for assessing their respective performance. Differential scanning calorimetry (DSC) and rheometry are the conventional techniques used for monitoring the curing processes leading to crosslinking polymerization of the adhesives. However, the direct comparison of these techniques is inappropriate due to the intrinsic differences in their underlying procedures. To address this challenge, the two adhesive samples were sequentially cured, firstly with rheometry and followed by DSC. The observed higher curing degree in the subsequent DSC procedure underpins the incomplete curing of the samples during initial rheometry. Furthermore, the comparative assessment of the activation energies, molar ratios, and active groups of the two adhesives highlights the importance of the pre-exponential factor in addition to the activation energies, as it attributes to the probability of active groups coinciding at the appropriate spatial arrangement.

Unravelling the thermal behavior and kinetics of unsaturated polyester resin supplemented with organo-nanoclay.

The integration of nanoclays within polymeric systems to develop high-performance materials is an emerging research field that has garnered significant attention. In this context, an organically modified montmorillonite (OMMT) is utilized as a reinforcing agent for unsaturated polyester resin (UPR) with loads of 1%, 3%, and 5 wt%. The modification of montmorillonite nanoclay (MMT) using a quaternary ammonium compound is performed through an effective repetitive modification process under reflux conditions. The curing behavior of the unsaturated polyester resin containing organically modified clay catalyzed with methyl ethyl ketone peroxide (MEKP) initiator and promoted by cobalt naphthenate accelerator is investigated using dynamic differential scanning calorimetry (DSC) followed by kinetic analysis using isoconversional methods. The dynamic DSC curing curves showed a bimodal exothermic peak, where two independent reactions, namely, redox and thermal decomposition of the initiator occurred. In this study, novel insights into the curing reaction of the studied UPR and UPR/OMMT systems have been revealed through the application of the Trache-Abdelaziz-Siwani (TAS) and Sbirrazzuoli (VYA/CE) isoconversional methods. These methods have enabled the elucidation of the intricate mechanisms and phenomena that impact the curing reaction, including the dilution effect in the redox reaction and the diffusion phenomenon at the end of the thermal decomposition reaction. The incorporation of nanoclay into unsaturated polyester resin (UPR) resulted in a reduction in the activation energy for both the redox and thermal reactions. Specifically, the energetic barrier decreased from 93.85 and 101.58 kJ mol-1 for pristine UPR to 60.71 and 72.93 kJ mol-1 for UPR/OMMT-5 in the redox and thermal reactions, respectively. The addition of OMMT caused a significant decrease in the pre-exponential factor. The values of UPR/OMMT-5 were 2.75 × 105 and 5.50 × 106 for the redox and thermal decomposition reactions, respectively, compared to 1.41 × 1012 and 5.13 × 1013 for UPR. The thermogravimetric analysis demonstrated that UPR/OMMT systems were more stable than UPR.

One-pot preparing EVA elastomer auxetic foam through stress relaxation of molecular chains by heat annealing

It is a challenge to prepare closed-cell auxetic foam by a simple method without destroying the properties of the foam. In this paper, auxetic foams were prepared directly from ethylene-vinyl acetate copolymer (EVA) resin in one step by annealing immediately after sc-CO2 foaming. The effects of annealing time and foaming temperature on the cell structure and Poisson's ratio were investigated using scanning electron microscopy (SEM) and Poisson's ratio testing. The reasons for the formation of EVA foams with negative Poisson's ratio were analyzed by dynamic mechanical thermal analysis (DMA) and differential scanning calorimetry (DSC). It was found that annealing treatment maintained the high movement ability of molecular chains and provided sufficient time for the molecular chains to relax, so that the stress generated by the foaming process can relax quickly and reach a new stable state, thus weakening the elastic shrinking of EVA foam. Under the action of the pressure difference between the inside and outside of the cell formed by the different diffusion rates of air and CO2, the cell concaves inward to produce a reentrant structure, and then the foam shape is fixed with the continuous improvement of crystallization. The obtained EVA auxetic foam has excellent resilience. Finally, it is proved that the method has good universality for the preparation of auxetic foams with most elastomers, so this study has important implications for the preparation of closed-cell elastomer polymer auxetic foams.

A numerical and experimental identification of crystallinity gradients in carbon fiber reinforced thermoplastic composites obtained by laser assisted filament winding

The presence of temperature and crystallinity gradients in carbon fiber–reinforced PolyEtherEtherKetone (PEEK) composite laminates, produced via laser-assisted tape placement, is investigated in this paper. The manufacturing process takes place with high deposition speed and using localized laser source for heating, therefore enhancing the formation of temperature and crystallinity gradients through the laminate thickness. A previously validated thermal model coupled with a non-isothermal crystallinity model and a fusion model are used to simulate the temperature and crystallinity distributions through the laminate thickness. The results from the model are correlated with Dynamic Mechanical Analysis (DMA) tests and Differential Scanning Calorimetry (DSC) tests since a crystallinity gradient is difficult to monitor experimentally. The simulated gradients suggested the presence of an amorphous layer between two consecutive plies and an increase in the crystallinity through the material’s thickness. This observation is correlated with the behavior reported for the semi-crystalline laminates during the DMA test, where the modulus drops abruptly during the glass transition, a typical behavior for an amorphous material.

3-D modeling of automatic pressure gelation process for manufacturing gas insulated switchgear spacer using bio-based epoxy composite

In existing power devices, various insulating parts are manufactured with petroleum-based epoxy resin. However, as petroleum-based resources are gradually depleted and environmental problems have emerged, research on replacing petroleum-based products with eco-friendly materials as insulators has been actively conducted. Therefore, in this study, a molding simulation study of the Auto Pressure Gelation (APG) process, one of the leading technologies, was conducted to manufacture a gas insulated switchgear (GIS) spacer using an environmentally friendly bio-based epoxy composite. Using the heat dissipation and degree of cure obtained through the dynamic differential scanning calorimetry (DSC) test, it was applied to the Kamal-Sourour model which is a representative curing dynamics empirical formula. In addition, the viscosity change during the curing process was measured using a rheometer and applied to the cross Castro-Macoskco model. The results obtained were in good agreement with the experimental values. The parameters calculated above and other physical property values were input into Moldflow software, and simulation was performed targeting the three-phase spacer. While changing the temperature setting of the mold, the change and distribution of flow, temperature, and curing degree inside the product were observed during the reactive molding process. As a result, it was found that there was a possibility of clogging of the mold entrance at some set temperatures, and it was possible to suggest improvement directions to solve this problem. Through this series of research process, it is considered that it will be of great help in improving the quality problems of molded products and the process accordingly.

Adhesives Based on Poly(glycidyl methacrylate‐co‐butyl acrylate) with Controlled Structure: Curing Behavior and Adhesion Properties on Metal Substrates

AbstractThe adhesion properties of poly(glycidyl methacrylate (GMA)‐co‐butyl acrylate (BA)) statistical copolymers, synthesized by atom transfer radical polymerization (ATRP), are investigated employing three different curing agents or hardeners, such as diethanolamine (DEA), dicyandiamide (DICY), and 2‐cyanoacetamide (2‐CA) on copper, iron, brass, aluminum, and titanium metal surfaces. This work describes the treatment of the different surfaces, establishes the optimal curing conditions from differential scanning calorimetry (DSC) analysis of these novel adhesive systems, and evaluates the results of the single‐lap shear test for metal joints. Thus, by dynamic DSC measurements of the mixtures, a low curing temperature of 90 °C is defined when DEA is used as a curative; while systems based on DICY and 2‐CA require temperatures of 150 °C and 160 °C, respectively. In addition, the curing process of this controlled acrylic copolymer with DICY exhibits a singular behavior, possibly due to the curing reaction mechanism, where multiple epoxy‐amine ring‐opening polyaddition reactions take place between DICY's active hydrogens and epoxy groups of poly(GMA‐co‐BA). This latter curing system shows the highest adhesion features with lap‐shear strength at room temperature of 15.5 MPa, using copper as metallic substrate; however, the best results are obtained using 2‐CA as curing agent with aluminum and iron.

Microwave-Assisted Silanization of Magnetite Nanoparticles Pre-Synthesized by a 3D Microfluidic Platform.

Magnetite nanoparticles (Fe3O4 NPs) are among the most investigated nanomaterials, being recognized for their biocompatibility, versatility, and strong magnetic properties. Given that their applicability depends on their dimensions, crystal morphology, and surface chemistry, Fe3O4 NPs must be synthesized in a controlled, simple, and reproducible manner. Since conventional methods often lack tight control over reaction parameters and produce materials with unreliable characteristics, increased scientific interest has been directed to microfluidic techniques. In this context, the present paper describes the development of an innovative 3D microfluidic platform suitable for synthesizing uniform Fe3O4 NPs with fine-tuned properties. On-chip co-precipitation was performed, followed by microwave-assisted silanization. The obtained nanoparticles were characterized from the compositional and microstructural perspectives by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Moreover, supplementary physicochemical investigations, such as Fourier Transform Infrared Spectroscopy (FT-IR), Kaiser Test, Ultraviolet-Visible (UV-Vis) Spectrophotometry, Dynamic Light Scattering (DLS), and Thermogravimetry and Differential Scanning Calorimetry (TG-DSC) analyses, demonstrated the successful surface modification. Considering the positive results, the presented synthesis and functionalization method represents a fast, reliable, and effective alternative for producing tailored magnetic nanoparticles.

Fabrication and characterization of transparent nanocomposite films based on poly (lactic acid)/polyethylene glycol reinforced with nano glass flake

Developing new biodegradable packaging with superior properties and advanced functionalities is one of the most emerging research areas of interest in food packaging. In this study, PLA/PEG-based nanocomposite films incorporated with different amounts of nano glass flake (NGF) (0, 0.5, 1, and 2 phr) were fabricated via casting solution for applications in food packaging. The ATR-FTIR displayed no chemical interaction between the PLA/PEG-based matrix and NGF particles. The scanning electron microscopy (SEM) observations exhibited a relatively smooth and homogeneous surface without defects. Incorporation of the NGF into the PLA/PEG-based matrix did not affect the color and opacity of the fabricated films. The prepared nanocomposite films were highly transparent and exhibited superior properties such as increased hydrophobicity, appreciable oxygen barrier properties, and enhanced thermal stability. Dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) analysis confirmed the existence of a single glass-transition temperature (Tg) as evidence of miscibility. According to the research results, the PLA/PEG/NGF1 nanocomposite film significantly offered the best overall performance. This work has developed new insight into the potential application of nano glass flakes in food packaging.

The synergistic impacts of hybrid nanofillers of graphene nanoplatelets/carbon nanotubes on curing behavior of an epoxy‐vinyl ester interpenetrating polymer network nanocomposite coating

AbstractThis study investigated the synergistic effects of hybrid graphene nanoplatelet (GnP)/multi walled carbon nanotube (MWCNT) nanofillers at various loadings on the kinetics of curing of the epoxy (EP)/vinyl ester (VE) interpenetrating polymer network (IPN) system, with a mass ratio of 1:1. Fourier transform infrared spectroscopy (FTIR), dynamic mechanical thermal analyzer (DMTA) and differential scanning calorimetry (DSC) were used to monitor the interpenetration process of EP and VE and likely interactions between the components of the different resin systems in IPN. The curing behavior of all prepared samples under non‐isothermal conditions was studied using DSC at four heating rates. Two different isoconversional approaches were applied to evaluate the reaction kinetics, that is, the Friedman and the advanced Vyazovkin methods. The obtained activation energy curves for all samples revealed a complex curing behavior involving three stages; early IPN stage, IPN growth stage, and late IPN stage. Then, the activation energy values for each reaction step were determined based on the Friedman method. The presence of GnP/MWCNT nanoparticles showed no catalytic effect on the reaction of VE with methyl ethyl ketone peroxide (MEKP). In contrast, incorporating GnP/MWCNT nanoparticles significantly decreases the activation energy values of the reaction of ring opening of epoxides with methyl tetrahydrophthalic anhydride (MTHPA) 1‐methyl imidazole (‐Mi) and the reaction of esterification of the hydroxyl groups of VE with MTHPA.Highlights Model‐free methods used to curing study of epoxy‐vinyl ester IPN nanocomposites FTIR, DSC and DMTA used for evaluation IPN formation of EP/VE It showed that the improvement of dispersion and compatibility by using of GnP/MWCNT hybrid Frideman and Vyazovkin methods used to calculate Ea of nanocomposites DSC thermograms were deconvoluted into three individual peaks.

Research on low temperature properties and physical hardening effect of asphalt components

It is generally recognized in current research that asphalt binder is composed of four components, i.e., saturates, aromatics, resins and asphaltenes, and the physicochemical properties of asphalt binder are closely related to the properties of the components. In this paper, solvent precipitation and chromatographic column method were used to extract and separate a sufficient amount of four components, and different components were recombinant according to the original ratio to form components recombinant materials. Using Fourier Transform Infrared, dynamic shear rheometer and differential scanning calorimetry to characterize the chemical composition and low temperature rheological properties of single component and components recombinant materials, including amplitude sweeping, temperature sweeping, time sweeping temperature-frequency sweeping and relaxation test. The response of the material to the physical hardening effect at low-temperature isothermal storage was also explored. The test results show that, within the test temperature range, the aromatics does not produce physical hardening effect, while the saturates and resins produced a certain degree of physical hardening effect. The free volume, phase angle, and complex shear modulus have different response times to the physical hardening effect, so the free volume theory alone is not sufficient to explain the physical hardening effect. This paper proposes to use the method of area integral to evaluate the degree of response of materials to physical hardening, and to rank the materials.

Poly(glycidyl methacrylate) modified cellulose nanocrystals and their PBAT-based nanocomposites

Melt processing of cellulose nanocrystals (CNCs) reinforced nanocomposites is still a serious challenge due to the hydrophilic nature of CNCs and their severe agglomeration tendency within the polymer melt. In this study, chemical modification of CNC through grafting poly(glycidyl methacrylate) (PGMA) with various degrees was implemented. Wettability of the modified CNCs (mCNCs) were controlled and their structure was characterized through Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), optical microscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The nanocomposites of polybutylene adipate terephthalate (PBAT) with 3 wt% CNC and mCNC were prepared using an internal melt mixer. To differentiate the effects of CNC and PGMA molecules on the final properties of nanocomposites, PBAT/PGMA compounds were separately prepared. To confirm the chain characterization and molecular weight of the synthesized PGMAs, 1H NMR and gel permeation chromatography (GPC) analysis were conducted. Melt rheological analysis, dynamic mechanical analysis (DMA), DSC, and atomic force microscopy (AFM) were used to monitor the mCNC dispersion quality and the effect of PGMA modification in PBAT compounds. The results revealed that grafting CNC with longer PGMA considerably improved the CNCs' dispersion quality within PBAT. Such dispersion enhancement of long-chain mCNCs and interfacial interaction of PGMA and PBAT resulted in a noticeable increase in storage modulus and complex viscosity of the final nanocomposites.

Experimental investigation of the recycling of carbon fiber polyetherketoneketone thermoplastic composite

The increasing usage of composite materials due to their lightness and high strength came along with a problem which is the accumulating waste of this material. Recycling is one of the sustainable waste management methods for composites. However, recycling of composite materials is a complicated process due to the complex nature of these materials where reinforcement and matrix are different components with different characteristics. In the evaluation of recycling methods for thermoplastic composites, many factors such as environmental effects and economic efficiency are taken into consideration. In this study, mechanical recycling of carbon fiber polyetherketoneketone (CF/PEKK) thermoplastic composite is carried out to show the feasibility of recycling by comparing the recycled and unprocessed material in terms of mechanical and thermal properties. Waste CF/PEKK materials are shredded and consolidated in a press and samples taken from the final product to carry out mechanical and thermal tests such as tensile, three-point bending test, dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Results indicate unprocessed thermoplastic composite shows 61% higher tensile strength and 79% fracture strength where recycled material shows a loss of 33% in flexural modulus.

Cure Kinetics of a Carbon Fiber/Epoxy Prepreg by Dynamic Differential Scanning Calorimetry

Investigating the curing kinetics of a fiber prepreg system is beneficial to the controlling of prepreg laminate curing process. In the present work, a dicyandiamide (DICY)-cured carbon fiber/epoxy prepreg system was investigated by non-isothermal differential scanning calorimetry (DSC) at 2, 5, 10, and 20°C/min to attain the glass transition temperature for uncured prepreg and fully cured sample, which were estimated to be 7.6°C and 106.2°C, respectively. The activation energy (Ea) of the prepreg system was evaluated by Kissinger and Ozawa methods, and Friedman method was also employed to reveal the evolution of Ea as a function of curing degree. The kinetic parameters were determined by fitting the average Ea value obtained by Friedman method into Málek methodology, and the two parameters Šesták–Berggren model was found to best describe the curing kinetic of the prepreg system. The preexponential factor was calculated to be 6.0 × 10 8 min−1, with the overall reaction order at nearly 2.5. The prediction curves, based on Friedman method and autocatalytic model, were in good agreement with the experimental data.

The effects of surface modified date‐palm fiber fillers upon the thermo‐physical performances of high density polyethylene‐polyvinyl chloride blend with maleic anhydride as a grafting agent

AbstractTo demonstrate the upcycling of thermoplastic waste with good thermo‐physical properties, high density polyethylene (HDPE; 80 phr) and polyvinyl chloride (PVC; 20 phr) are mixed as the matrix using maleic anhydride (MAH) reinforced with unmodified and modified date palm fibers (DPFs; 30 phr). The effects of in situ grafting of MAH onto the DPFs‐HDPE‐PVC composites upon the resultant thermo‐physical characteristics are investigated and analyzed via Fourier transform infrared spectroscopy and scanning electron microscopy. Thus, the effective compatibilizing of both the HDPE‐PVC component and the grafted HDPE‐PVC blend with the modified DPFs are confirmed. In addition, the results of dynamical mechanical analysis and differential scanning calorimetry indicate that the glass transition temperature (Tg) of the composite is enhanced by the incorporation of modified DPFs. The thermal, mechanical, and water uptake properties of the composites are also improved. Rheological analysis at low frequency reveals that the introduction of hydrolyzed DPFs results in a higher complex viscosity (1.94 × 106 Pa s) and storage modulus (119,844 MPa) for the obtained composite (designated G‐Hydro). Overall, the G‐Hydro composite exhibits the best performance, making it ideal for a variety of construction and building purposes.

Mechanical vs calorimetric glass transition temperature in the oxidation of linoleic acid from condensed κ-carrageenan/glucose syrup systems

Lipid oxidation remains a concern leading to deterioration of the organoleptic quality in processed goods, but it should be minimized by considering changes in the structural properties of foods. The present work investigates the effect of glass transition temperature on the oxidation of linoleic acid at different concentrations of κ-carrageenan/glucose syrup. A combination of 0.5, 1, 2 and 3% (w/w) κ-carrageenan and 82.5, 82, 81, 80% (w/w) glucose syrup were mixed with 1.5% (w/w) linoleic acid and 0.5% (w/w) lecithin to prepare samples with a total solid content of 85% (w/w). Physicochemical properties of these mixtures were recorded using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). This was followed by estimation of the mechanical (Tgm) and calorimetric (Tgc) glass transition temperatures using small deformation dynamic oscillation in-shear and modulated differential scanning calorimetry (MDSC). The linoleic acid oxidation in the condensed polysaccharide/co-solute system was evaluated by monitoring the accumulation of hydroperoxide (ROOH) with UV–vis spectroscopy over a wide temperature range (−25 to 0 °C). The oxidation phase was modelled following a sigmoidal kinetic model indicating initiation and propagation stages of lipid oxidation. ROOH production increased as a function of time and temperature. The structural relaxation of the polymeric matrix influenced the oxidation rate at the initiation stage. At the propagation phase, Tgm appears to control the rate of ROOH formation (kf) and decomposition (kd) in all preparations, as compared to Tgc, an outcome that makes the former an important concept of quality control.