Dynamic Differential Scanning Calorimetry Research Articles

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.

Waterborne polyurethane via encapsulated blocked isocyanate crosslinker for 1 K clearcoats

Herein, a waterborne polyurethane clearcoat with excellent chemical and physical performance through an encapsulation system has been developed. The encapsulation system in this study incorporated blocked polyisocyanate (b-PIC) as a crosslinker with an acrylic polyol to ensure homogeneous dispersion under water-based conditions. An acrylic polyol was designed to readily disperse into the water phase, fulfill the requirements of a clearcoat, and effectively encapsulate b-PIC. The structure of the core-shell encapsulation system enabled both homogeneous dispersion and close proximity between the acrylic polyol and b-PIC, resulting in a uniform crosslinking clearcoat. Three different clearcoats were prepared: two water-based b-PIC systems with both polyisocyanate encapsulated dispersion (PED) and conventional b-PIC dispersion (CPD) without encapsulation, and a solvent-based (SB) b-PIC dispersion with ethyl cellosolve. Their crosslinking and mechanical properties were characterized. Using dynamic light scattering (DLS), it was confirmed that PED contained synthesized encapsulated particles smaller than 80 nm with a narrow particle size distribution. The cured PED-containing clearcoat exhibited a higher gloss of 73.6 at 20° compared to that of CPD. In addition, the surface mechanical properties of cured PED waterborne clearcoat using pencil hardness, nano-indentation (NI), and micro-scratch testing (MST) were measured. In particular, the PED clearcoat exhibited superb resistance to water penetration, maintaining more than 95 % transmittance using a UV–Vis spectrometer. Finally, the glass transition temperature of PED, CPD, and SB clearcoats was confirmed by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). These indicated that the PED clearcoat system could be utilized in waterborne coatings technology as a useful and inexpensive technology that addresses the need to reduce volatile organic compound (VOC) production for improved environmental protection.

Dynamic Cyclic Fatigue and Differential Scanning Calorimetry Analysis of R-Motion

The aim of this study was to assess the dynamic cyclic fatigue resistance of an R-Motion file at simulated body temperature and document corresponding phase transformations compared to OneCurve and HyFlex EDM (HFEDM). R-Motion (25/.06), OneCurve (25/.06), and HFEDM (25/.06) files were selected and divided into 3 groups (n=9) according to the file type. Dynamic cyclic fatigue testing was done with a custom-made artificial stainless-steel canal that had a 90° angle of curvature and a 5-mm radius of curvature. Files were operated continuously at body temperature until fracture in the artificial canal. The time to fracture was calculated. Statistical analysis was performed, and significance was set at 5%. Phase transformation temperatures for 2 instruments of each group were analysed by differential scanning calorimetry (DSC) analysis. The highest mean time to fracture value was measured in the HFEDM group (277.84 ± 2.51), followed by the R-Motion group (115.09 ± 0.01), whilst the lowest value was found in the OneCurve group (44.28 ± 3.63). Post hoc pairwise comparisons were all statistically significant (P < .001). DSC heating curves show austinite start temperatures to be 33.94 °C and 43.32 °C and austinite finish temperatures to be 35.09 °C and 50 °C for R-Motion and HFEDM, respectively. DSC cooling curves show martensite start temperatures to be 27.54 °C and 44.52 °C and martensite finish temperatures to be 29.13 °C and 37.68 °C for R-Motion and HFEDM, respectively. DSC curves of OneCurve failed to demonstrate transformation temperatures within the tested heat range. Crystalline arrangement of Ni and Ti atoms within the NiTi alloys greatly affects the dynamic cyclic fatigue resistance of the file.

Characterization and its curing behaviors of rigid phenolic foams based on cardanol

Cardanol/phenol-based foaming resol resins were prepared successfully by reacting formaldehyde with cardanol/phenol. Phenolic foams were fabricated with the above foaming resol resin and certain foaming agents. Two kinds of resol resins were characterized with Fourier transform infrared spectroscopy, rheological analysis and Scanning electron microscope. Meanwhile, the nonisothermal curing reactions of these resol resins were studied in detail using a dynamic Differential scanning calorimetry technique at a series of heating rates. The global activation energies of the reactions were determined with the Ozawa methods. The results indicated that the peak temperatures of the exothermic reactions and global activation energies of cardanol-based foaming resol resin were higher than those of phenol-based foaming resol resin, which indicated that the more complex molecular structure of cardanol-based foaming resol resin has a negative effect on the curing speed of resin.

Influence of UV Ageing on Properties of Printed PLA Containing Graphene Nanopowder.

The present paper analyses the properties of printed polylactic acid (PLA) samples with admixtures of graphene nanopowder (GNP) at wt. 1%, 2% and 4%. The pure polylactide and admixed polylactide printed samples were examined to determine their chemical-physical properties, stiffness, and strength parameters. The tests of tensile, dynamic mechanical analysis (DMA), difference thermogravimetric (TG), and differential scanning calorimetry (DSC) were executed before and after UV (ultraviolet) treatment. The first part of the paper shows the process of manufacturing granulates and filaments mixed with graphene. The second part of the paper concerns the results of the tests made on printed samples. The analysed samples were printed using a Prusa i3 MK3 printer. It transpired that the content of graphene at 1% improved the mechanical parameters of the printed composite by organising its structure. Increasing the amount of graphene caused the values of the measured parameters to drop. This research indicates how important it is to determine the optimal values of nanoadditives in biopolymers.

Physical and Oxidative Water-in-Oil Emulsion Stability by the Addition of Liposomes from Shrimp Waste Oil with Antioxidant and Anti-Inflammatory Properties.

Liposomes made of partially purified phospholipids (PL) from Argentine red shrimp waste oil were loaded with two antioxidant lipid co-extracts (hexane-soluble, Hx and acetone-soluble, Ac) to provide a higher content of omega-3 fatty acids. The physical properties of the liposomes were characterized by Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) and Differential Scanning Calorimetry (DSC). The antioxidant and anti-inflammatory activity of the lipid extracts and liposomal suspensions were evaluated in terms of Superoxide and ABTS radical scavenging capacities and TNF-α inhibition. Uni-lamellar spherical liposomes (z-average ≈ 145 nm) with strong negative ζ potential (≈ -67 mV) were obtained in all cases. The high content of neutral lipids in the Hx extract caused structural changes in the bilayer membrane and decreased entrapment efficiency regarding astaxanthin and EPA + DHA contents. The liposomes loaded with the Hx/Ac extracts showed higher antioxidant and anti-inflammatory activity compared with empty liposomes. The liposomal dispersions improved the physical and oxidative stability of water-in-oil emulsions as compared with the PL extract, inducing pronounced close packing of water droplets. The liposomes decreased hydroperoxide formation in freshly made emulsions and prevented thio-barbituric acid-reactive substances (TBARS) accumulation during chilled storage. Liposomes from shrimp waste could be valuable nanocarriers and stabilizers in functional food emulsions.

Aspects of halloysite nanotubes integration in epoxy nanocomposites: Curing kinetics and deformation mechanism

AbstractThe curing kinetics of diglycidyl ether of bisphenol A epoxy resin using amine‐based hardener in the presence of halloysite nanotubes (HNTs) are investigated by performing isothermal and dynamic differential scanning calorimetry measurements, followed by a detailed analysis of the experimental data via the kinetic free method and three common model‐based analysis. Kamal and Sourour model gave the best fit for the experimental data and thus, was further modified by Williams–Landel–Ferry diffusion control equations to calculate the diffusion constants near the glass transition temperature (Tg). The optimized model is used to find the curing kinetics parameters of epoxy/HNTs nanocomposites, and those finding are further validated and explained by performing rheometric measurements. Noncatalytic and autocatalytic curing reactions and diffusion constants are all functions of the amount of HNTs. HNTs shift the curing reaction slightly toward higher temperatures and promote etherification reactions, leading to an increase in the curing enthalpy, as extra bonds will be formed between HNTs and epoxy resin during the polymerization. The combination of acceleration and inhibition mechanisms dictates the complex kinetics of the reactions at high concentrations of HNTs, while the produced local topology of the polymeric network depends highly on HNTs weight ratio. Furthermore, to investigate the mechanical performance of the prepared nanocomposites under flexural loads, three points bending tests are performed in both modes, dynamic and static, followed by a fractography analysis of the fractured surfaces. The mechanical properties have improved by the addition of pristine HNTs without compromising the Tg of the polymer. This study provides a set of observational relationships between various chemical interactions during polymerization and the final topology and performance of the polymer, which in turn aims to bridge the gap in the literature between the curing kinetics of epoxy/HNTs nanocomposites and the performance of these nanocomposites under various thermal and mechanical stresses.

Influence of a Hydride-Forming Multi-Component Alloy on the Carbonization Behavior of Vulcanized Elastomer Composites

In this work, composites based on a hydride-forming fiber of a multi-principal-component (MPC) Ti20Zr20Nb20V20Hf20 alloy, carbosil, dicumylperoxide and nitrile butadiene rubber (NBR) matrix were obtained. The composites were prepared in a three-stage process including the mixing of elastomeric compounds via a rubber mixing mill and low-temperature vulcanization by heat pressing. Using dynamical mechanical analysis (DMA) and differential scanning calorimetry (DSC) the effect of the metallic filler on the process of carbonization of the composite elastomeric matrix was studied. The microstructure and gas separation properties of the resulting composites were also studied. The results showed that the filler content increase in the elastomeric matrix leads to a noticeable and gradual decrease in the activation energy of the carbonization process, reduces the temperature of this process, and accelerates the growth of the elastic modulus during carbonization. It was shown that the finely dispersed fiber of the MPC acts as an activation center for the process of thermal-oxidative degradation in the elastomeric matrix accompanying the onset of carbonization. The gas permeability values were found to be relatively low and no visible correlation with the MPC alloy content in the composite membrane was observed.

Polylactic Acid Chemical Foaming Assisted by Solid-State Processing: Solid-State Shear Pulverization and Cryogenic Milling.

A chemical foaming process of polylactic acid (PLA) was developed via the solid-state processing methods of solid-state shear pulverization (SSSP) and cryogenic milling. Based on the ability of solid-state processing to enhance the crystallization kinetics of PLA, chemical foaming agents (CFA) are first compounded before foaming via compression molding. Specifically, the effects of the pre-foaming solid-state processing method and CFA concentration were investigated. Density reduction, mechanical properties, thermal behavior, and cell density of PLA foams are characterized. Solid-state processing of PLA before foaming greatly increases the extent of PLA foaming by achieving void fractions approximately twice that of the control foams. PLA's improved ability to crystallize is displayed through both dynamic mechanical analysis and differential scanning calorimetry. The solid-state-processed foams display superior mechanical robustness and undergo low stress relaxation. The cell density of the PLA foams also increases with solid-state processing, especially through SSSP. Additionally, crosslinking of PLA during the pre-foaming processing step is found to result in the greatest enhancement of crystallization but decreased void fraction and foam effectiveness. Overall, SSSP and cryogenic milling show significant promise in improving chemical foaming in alternative biopolymers.

Cyclotriphosphazene-based epoxy resins with excellent mechanical and flame retardant properties

The design, synthesis, and characterization of a novel epoxy monomer, CP-EP, which consists of nontoxic eugenol and nonflammable cyclotriphosphazene has been carried out in this work. Chemical structure of CP-EP was confirmed by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). Using 4,4′-diaminodiphenylmethane + diethyltoluenediamine (DDM + DETDA), succinic anhydride (SA), or methylhexahydrophthalic anhydride (MeHHPA) as curing agent, three cyclotriphosphazene-based thermosets (CPTs) were produced, and non-isothermal curing behaviors were investigated by using dynamic differential scanning calorimetry. In comparison to the bisphenol-A epoxy resin, CPTs exhibit higher glass transition temperature, enhanced tensile/flexural strengths, and significantly improved nonflammability. UL-94 rating and limiting oxygen index (LOI) for CPTs were V-0 and 28% respectively. These observations suggest an effective approach for the preparation of a halogen-free epoxy thermosetting system. This approach may be used for the generation of high-performance fire-safe epoxy thermosets. Both environment and human health can benefit from the use of such materials.

Effect of stoichiometry on chemical structure, dielectric and mechanical properties of epoxy resin under gamma irradiation

The chemical and physical properties of diglycidyl ethers of bisphenol-A (DGEBA)/2,2'-(ethylenedioxy) bis(ethylamine) (EDBA) epoxy resins with different stoichiometric ratios under gamma irradiation have been investigated. Fourier transform infrared (FTIR) spectroscopy results indicated that a mass of amines and oxidized carbonyl-containing products were generated during the irradiation process. Most products for amine-rich DGEBA/EDBA systems were amides. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) results demonstrated that chain scission predominated during irradiation for the amine-rich system, while chain cross-linking predominated for the epoxy-rich system. The dielectric relaxation behaviours indicated that the α relaxation behaviours broadened considerably with an increasing irradiation dose, demonstrating an increasing spatial heterogeneity of the crosslinked networks. The compressive yield strengths showed a monotonous linear increase with irradiation dose. However, due to the different cross-linking networks, the yield strains showed converse trends for amine-rich and epoxy-rich systems under gamma irradiation.

Cationic Copolymers of Norbornylized Seed Oils for Fiber-Reinforced Composite Applications.

Norbornylized seed oils, i.e., norbornylized linseed oil (NLO), norbornylized soybean oil (NSO), and norbornylized high oleic soybean oil (NHOSO), were synthesized via the Diels–Alder reaction of seed oil and dicyclopentadiene (DCPD) at high temperature (∼235 °C) and high pressure (∼80 psi), followed by cationic copolymerization using DCPD with boron trifluoride diethyl etherate catalyst. Norbornylized seed oils were characterized using H1 nuclear magnetic resonance (NMR), attenuated total reflectance-Fourier transform infrared, and gel permeation chromatography (GPC). Copolymers were formulated with four different DCPD contents, and curing was investigated using dynamic differential scanning calorimetry (DSC) measurements. It was found that the curing followed NLO > NSO > NHOSO with NLO having the highest exotherm, lowest activation energy, and lowest onset temperature. Furthermore, the gelation times were the least for NLO-DCPD copolymers. As anticipated, the degree of unsaturation and norbornene moieties strongly influenced the curing of copolymer thermosets. The copolymer products were compression-molded into thermosets and characterized by DSC, Soxhlet extraction, thermogravimetric analysis (TGA), H1 NMR, solid-state C13 NMR, and GPC. NLO-DCPD thermosets demonstrated high cure, higher thermal stability, glass transition temperature, and cross-linking capability compared to the other seed oil-DCPD counterparts. NMR and GPC results further suggested that bis-allylic and norbornene units concomitantly participated very actively during the cationic curing reaction. Moreover, scanning electron microscopy images of glass fiber-reinforced NLO-DCPD copolymer composites demonstrated good interfacial adhesion between the polymer matrix and fiber phases, imparting enhanced thermo-mechanical properties. This research opens a new venue for higher biobased greener polymer constituent for composite applications.

The Combined Effect of Ambient Conditions and Diluting Salt on the Degradation of Picric Acid: An In Situ DRIFT Study.

An unexpected promoting effect of KBr, used as a diluting salt, on the degradation of picric acid (PA) was observed during in situ diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy experiments performed here under accelerated ageing conditions—at 80 °C and under an inert or oxidative atmosphere. While the formation of potassium picrate was excluded, this promoting effect—which is undesired as it masks the possible effects of test conditions on the ageing process of the material—was assumed to favor a first step of the decomposition mechanism of PA, which involves the inter- or intramolecular transfer of hydrogen to the nitro group, and possibly proceeds up to the formation of an amino group. An alternative diluting salt, ZnSe, which is much less commonly used in infrared spectroscopy than KBr, was then proposed in order to avoid misleading interpretation of the results. ZnSe was found to act as a truly inert diluting salt, preventing the promoting effect of KBr. The much more chemically inert nature (towards PA) of ZnSe compared to KBr was also confirmed, at much higher temperatures than DRIFT experiments, by dynamic differential scanning calorimetry (DSC) runs carried out on pure PA (i.e., PA without salt) and PA/salt (ZnSe or KBr) solid mixtures.

Mechanical and chemical analysis of structural silicone adhesives with the influence of artificial aging

Structural sealant glazing systems, or bonded glazing, refers to façades in which the glass is structurally bonded to a façade frame and which is typically used in large façades for office buildings. The structural silicone bond lines are an essential element of such façades and a variety of environmental influences and aggressive media interact with the adhesive and may affect its performance. The ETAG 002 is commonly used for the verification of the technical applicability taking these effects into account. In this study, samples of an approved standard silicone adhesive and a high-modulus silicone adhesive are artificially aged according to ETAG 002 and exposed to a climate change test. The aim of this study is to determine the essential mechanical properties and to explain the changes due to aging by means of chemical analysis. Polymer degradations are determined by evaluating the molecular structure with Fourier-transform Infrared Spectroscopy and Thermo-Gravimetric analysis. In addition, water absorption is investigated with Karl Fischer titration. Changes in the chemical structure are particularly identified after aging in SO2 atmosphere as well as after UV exposure. Increased water contents are detected for all specimens conducted to high moisture. The mechanical properties as well as their characteristic temperature ranges are determinate by the Dynamic Mechanical Analysis and Differential Scanning Calorimetry. The results of the study show significant loss of the adhesive stiffness up to 30% after artificial aging, mainly after storage in cleaning agent and after climate change test. However, there are no significant chemical effects of both aging methods on the adhesives. On the other hand UV-radiation as well as the acid attack, interact with the polysiloxane and the filler of the adhesive. This shifts the crystallization temperature a bit but it does not influence the adhesive stiffness at room temperature. Finally, tensile tests and shear tests are performed on both reference and aged bonded glass–aluminum specimens. These test confirm the good durability of silicone adhesives and the results meet the requirements of the ETAG 002.

Evolution of PEKK crystallization measured in laser sintering

The rising popularity of laser sintering (LS) technology has increased by the broadening of available materials for this process. Kepstan 6002 poly (ether ketone ketone) (PEKK) was recently launched as a high-performance polymer grade with a lower processing temperature and unique crystallization kinetics. This study aims to understand the progress of crystallization on samples manufactured throughout the laser sintering process. These results were compared with isothermal and dynamic differential scanning calorimetry (DSC) experiments with different cooling rates. Kepstan 6002 PEKK processed by high-temperature laser sintering (HT-LS) presents a kinetics of crystallization in the order of ∼10 times slower than its crystallized samples in the DSC. This result highlights the need for a part-based crystallization investigation rather than isothermal models to describe the crystallization in LS. The transmission electron microscopy (TEM) analysis reveals smaller spherulites in the samples subjected to prolonged cooling times and an almost amorphous structure for the PEKK samples exposed to almost no cooling. This experiment identified the surroundings of laser sintered particles as preferential sites for crystallization initiation, which grows as the particles penetrate the molten layers and spherulites are formed. The slower kinetics of crystallization of Kepstan 6002 PEKK grade improve the adhesion between layers in laser sintering and enable tailoring its properties according to the application. Understanding the relationship between intrinsic material characteristics and the resulting final properties is vital to optimizing the process and controlling the final performance of PEKK for different applications.