DMA Tests Research Articles

Influence of Thermomechanical Treatments and Chemical Composition on the Phase Transformation of Cu-Al-Mn Shape Memory Alloy Thin Sheets

This paper investigates the interrelated effects of thermomechanical treatments and chemical composition on the phase transformation capabilities of thin sheets made from Cu-Al-Mn shape memory alloys. The transformation capacity and transition temperatures were determined using DSC and DMA testing, while composition measurements were performed using SEM/EDX analysis. The results demonstrate that applying hot-rolling treatments to alloys of reduced thickness leads to manganese oxidation and modifications in chemical composition, adversely impacting the phase transformation performance. This effect can be mitigated by the use of cold rolling. Additionally, the presence of phosphorus impurities can create inclusions that bind manganese, preventing it from remaining in the solid solution and further affecting phase transformation capabilities.

Impact of Graphene Nano particles on static and dynamic mechanical properties of basalt-glass fibre reinforced epoxy polymer hybrid composites

ABSTRACT This paper investigates the structure-property relationships in basalt – glass fabric reinforced hybrid polymer composites doped with graphene nanoplatelets. Basalt Glass fabrics were reinforced with 0.2 wt.% − 0.8 wt.% graphene using hand layup and compression moulding to fabricate laminated plates. The mechanical, morphological, and thermomechanical properties were characterised using tensile, flexural, impact, SEM, FTIR, XRD, and DMA testing. Results showed that low graphene loadings of 0.2 wt.% − 0.4 wt.% led to small, isolated graphene platelets decorating the basalt fibres. At 0.8 wt.% loading, extensive wrinkling, folding, and stacking of graphene sheets on the basalt was observed. FTIR revealed increasing sp2 C=C vibrations and XRD showed rising graphene peak intensities with higher loadings. While tensile and flexural strengths improved up to 0.6 wt.% graphene due to efficient stress transfer, impact energy increased consistently until 0.8 wt.% graphene owing to reinforcement effects. DMA exhibited enhanced storage modulus and restricted mobility with more graphene. An optimum graphene loading of 0.6 wt.% was found to maximise the mechanical performance through uniform dispersion and strong interfacial adhesion. The results demonstrate that graphene incorporation can substantially augment the strength, toughness, and thermomechanical properties of the composites at appropriate compositions prior to aggregation.

Enhanced Thermal and Flexural Properties of Alkalized Date Palm/Kenaf Fiber-Reinforced Epoxy Hybrid Composites: A Comparative Study of Untreated and Treated Fibers

ABSTRACT This study evaluates the thermal and mechanical behavior of hybrid composites made from date palm (DP) and kenaf fibers (KF) in an epoxy thermoset matrix. Both DP and KF fibers are abundant and renewable, reducing environmental impact. KF offers high tensile strength and stiffness, improving composite strength and rigidity, while DP fibers offer toughness and impact resistance, enhancing durability. The composites were developed in 30%, 50%, and 70% DP-KF compositions using layup and hot-pressing methods. Fiber treatment through alkalization was analyzed for its impact on mechanical and thermal properties to find the optimal fiber ratio. The hybrid composites were subjected to DMA, TGA, and flexural tests. The treated composites exhibited fewer impurities and increased cellulose content, resulting in enhanced flexural performance. This improvement was evident through higher storage modulus, lower loss modulus, and reduced tan δ when exposed to thermal stress. The 30% DP and 70% KF composites exhibited best performance. The treated 30DP-70KF exhibited improvement in the flexural strength and modulus by 13.8% and 2.7%, respectively. TGA demonstrated that treated 30DP-70KF composites had a higher glass transition temperature (Tg) and better thermal degradation resistance. These findings highlight the potential of natural fiber hybrids in creating sustainable, high-performance composite materials for construction and industrial applications.

Comparing tensile, bending and interlaminar shear performance of GFRP composites fabricated using recovered and virgin glass fibers: Optimization of the microwave assisted chemical recycling technique

AbstractGlobal glass fiber reinforced plastic (GFRP) recycling provides an effective solution to the end‐of‐life wastes and industrial scrap, by which we can construct a closed‐loop system that reduces environmental impact while increasing sustainability. This study reports the tensile, flexural and shear properties of GFRP composites fabricated from reclaimed fibers from the waste GFRP. A hybrid recycling technique that is, microwave assisted chemical recycling has been used for recovering the glass fiber fabrics. The quantity of solvents (a mixture of 30% H2O2 and CH3COOH in 1:1 ratio) required (in mL/g) for degrading the polymer is optimized with respect to the amount of microwave irradiation time. The microwave irradiation duration was varied at constant power of 900 W for optimizing the quantity of solvent used. SEM analysis of both virgin and reclaimed fiber surfaces indicate an almost complete degradation of polymer from the waste composites. RGFE laminates, fabricated from reclaimed glass fiber fabrics, exhibited marginally higher tensile strength (7%–8%) and significant lower tensile modulus (~29%). On the other hand, RGFE composites demonstrated a greater strain to failure of ~44% compared to VGFE composites during tensile testing, consequently leading to a subsequent increase in tensile toughness by ~28%. The ILSS values obtained from SBS tests and storage modulus and loss factor curves from DMA tests showed almost similar values. SEM studies revealed the probable causes of failures of the samples for tensile and flexural tests.Highlights Hybrid recycling technique using microwave irradiation is optimized. Amount of solvent used is optimized by varying the irradiation times. Tensile and flexural strengths exhibit a marginal increase of 7%–8%. Significant rise in strain at failure by 44% and tensile toughness by 28%. Fractography studies have been performed for analyzing failures.

A 3D finite strain constitutive model for shape memory polymers combined viscoelasticity and storage strain

A 3D finite strain constitutive model combined viscoelasticity and storage strain for shape memory polymers (SMPs) is proposed. SMPs are phenomenally regarded as a homogeneous material of the viscoelastic glassy phase and hyperelastic rubbery phase in this model. Based on energy decomposition, the constitutive equation is derived using Clausius inequality and unified Helmholtz free energy. Then, an analytical expression for storage strain is presented, significantly simplifying the prediction of shape memory recovery process. The model is implemented in MATLAB and the commercial finite element software package ABAQUS using the UMAT subroutine. Our additional DMA tests and experimental data from the literature for various SMPs with different shape structures are used to verify the proposed model. All simulation results demonstrate the effectiveness of the proposed model in predicting the shape memory effect and complex thermomechanical behaviors of various SMPs.

Morphological, Thermal, and Mechanical Properties of Nanocomposites Based on Bio-Polyamide and Feather Keratin-Halloysite Nanohybrid.

One solution to comply with the strict regulations of the European Commission and reduce the environmental footprint of composites is the use of composite materials based on bio-polymers and fillers from natural resources. The aim of our work was to obtain and analyze the properties of bio-polymer nanocomposites based on bio-PA (PA) and feather keratin-halloysite nanohybrid. Keratin (KC) was mixed with halloysite (H) as such or with the treated surface under dynamic conditions, resulting in two nanohybrids: KCHM and KCHE. The homogenization of PA with the two nanohybrids was conducted using the extrusion processing process. Two types of nanocomposites, PA-KCHM and PA-KCHE, with 5 wt.% KC and 1 wt.% H were obtained. The properties were analyzed using SEM, XRD, FTIR, RAMAN, TGA, DSC, tensile/impact tests, DMA, and nanomechanical tests. The best results were obtained for PA-KCHE due to the stronger interaction between the components and the uniform dispersion of the nanohybrid in the PA matrix. Improvements in the modulus of elasticity and of the surface hardness by approx. 75% and 30%, respectively, and the resistance to scratch were obtained. These results are promising and constitute a possible alternative to synthetic polymer composites for the automotive industry.

Thermodynamic prediction of filler surface modification by APTES on corrosion resistance of nano-TiO2/waterborne epoxy coatings

Common techniques for creating novel coatings include chemically modifying inorganic fillers and exploring how modifications affect coating service performance. However, it frequently takes a lot of time and tedious attempts to get the ideal alteration degree for fillers. Although the surface energy of the fillers is thought to be a significant thermodynamic parameter, it is still unknown how chemical modification affects surface energy and how the properties of fillers in a coating relate to the quantization difference of thermodynamic parameters. In this study, the impact of chemical modification on the quantization difference of nano-TiO2 surface energy has been uncovered. Creating a “wetting-reagglomeration-adsorption” isogram by utilizing three surface interfacial parameters has also been achieved: the contact angle between the liquid resin and the filler, the driving energy of the filler reagglomeration, and the polymer molecules' diffusion energy at the filler/coating interface. The relationship between the quantitative difference of thermodynamic parameters and the dispersion, compatibility and interfacial strength of the fillers in the waterborne epoxy was predicted by the isocontour map. From the isocontour map, the modified nano-TiO2 fillers with 4.04 APTES molecules/nm2 shows the minimum ∆Wa of 16.17 mJ/m2 and the maximum Ws of 23.15 mJ/m2 in the composite coating, which is predicted to exhibit the best dispersibility and the strongest interfacial strength. The prediction results were successfully verified by the techniques of microscopic morphology observation (TEM and SEM), mechanical properties tests (DMA and tensile tests), and corrosion resistance tests (EIS and salt spray tests). This work has a significant guiding role in the development of the filler modifications for the creation of novel coatings.

Thermomechanical properties of poly(vinyl alcohol) prepared at room temperature as a function of degree of hydrolysis and aluminium addition

Poly(vinyl alcohol) (PVOH) is widely used in various industrial applications. However, its water solubility reduces film performance, which is important in PVAc-based wood adhesives. In this sector, AlCl3 is often used as a complexing agent for PVOH. In this work, the effect of heating and aluminium addition on the structure and viscoelastic properties of PVOH with different degrees of hydrolysis (DH), 88%, 92% and 99%, was studied. Products treated with either HCl or acetic acid were also considered. The polymer properties were evaluated by infrared spectroscopy and dynamic mechanical analysis, and the mass loss of the polymers on heating was also evaluated to explain the observed differences. The measurements showed that the peaks of the tanδ curves occurred at slightly lower temperatures as the DH increased, although higher crystallinity was observed at the end of the DMA tests for higher DHs. This is due to the increasing affinity of highly hydrolysed PVOH for water molecules. However, as the temperature increased, the storage modulus was higher for higher DHs due to the better mutual interaction of OH groups that develops during the tests in highly hydrolysed polymers. The addition of aluminium caused a slight increase in Tg, the magnitude of which was inversely proportional to the DH. However, as the temperature increased, the storage modulus decreased more at lower DHs than at higher DHs. This effect was related to a combination of factors: the lower presence of crystallites in products with lower DH and the formation of conjugated polyenes, which was also more pronounced in products with lower DH. Both mechanisms were due to the action of aluminium. Thus, both heat and the addition of aluminium had a determining effect on the properties of PVOH films, although the degree of importance depended on the degree of hydrolysis of the polymer.

Polyetherimide nanocomposite with enhanced mechanical, thermal and dielectric properties by incorporating synergistically exfoliated‐chemical functionalization induced hexagonal boron nitride nanosheets

AbstractThe present study aims to improve the mechanical, thermal and dielectric properties of polyetherimide (PEI) nanocomposite via simplified method, involving the creation of a nanocomposite using PEI incorporated with exfoliated‐chemical functionalization induced hexagonal boron nitride nanosheets (BNNS). XRD, FTIR and Raman elucidated the chemical structure of functionalized BNNS and indicated the success preparation of functionalized BNNS. Functionalization effectively improved the compatibility of nanocomposites and contributed to the property improvements. Morphological analysis unveiled a compact and dense microstructure within the nanocomposites in correlation with functionalized BNNS. Broad band dielectric spectroscopy revealed excellent dielectric properties of produced PEI nanocomposite. DMA testing verified a noteworthy enhancement in both Tg and storage modulus upon incorporating of BNNS. In summary, this comprehensive investigation highlights the impact of functionalized BNNS on mechanical, thermal and dielectric properties of developed PEI dielectric nanocomposite and is expected to expand the application of PEI in the field of high‐temperature energy storage.Highlights Polyetherimide (PEI) was used as polymer matrix and boron nitride derivatives as dielectric fillers to prepare PEI dielectric nanocomposite. Due to the influences of dielectric properties by interface polarization effect and the local distribution of electric field of the fillers in PEI matrix, the dielectric constant, breakdown strength and energy storage density of PEI nanocomposites were obviously improved compared with pure PEI. The effects of interfacial interactions between PBNNS and PEI contributes to the uniform dispersion and comprehensive property improvements of PEI dielectric nanocomposites. This work presents a systematic investigation into the fabrication of PEI/BNNS nanocomposite using a one‐step solution blending method, inspiring the research and development of PEI in the energy storage applications areas in the future.

Binary-Network structured PI@SiO2 nanofibrous composite aerogels with temperature invariant superelasticity for thermal insulation

The extreme temperatures encountered in aerospace pose formidable challenges to the performance of elastic materials in spacecraft and related apparatus. Traditional organic insulation materials face hindrance due to inadequate fire resistance, while inorganic insulation materials are often brittle. Herein, we designed binary-network composite aerogels with dual-crosslinked PI nanofibers as the scaffold and uniformly distributed silica nanoparticles within the anisotropic aerogel matrix. Owing to the dual-crosslinked PI nanofiber network, the resulting PI@SiO2 aerogel can withstand 1000 cycles of radial fatigue testing under 50 % compressive or buckling strains, maintaining structural stability across a wide angular frequency range of 0.1–100 rad/s. DMA testing shows that PI@SiO2 aerogel can endure 100,000 fatigue cycles from 25 to 300 °C, with storage modulus and loss modulus, and damping ratio, indicating robust long-term performance over a wide temperature spectrum. Even with liquid nitrogen (−196 °C) and butane torch flames (1100 °C), PI@SiO2 aerogel preserves its superelasticity through repeated compressions. Moreover, the composite aerogel exhibits excellent thermal insulation, with low thermal conductivity (27.2 mW m−1 K−1), and reachs the top flame-retardant level (UL94-V0). This work not only establishes a novel pathway for constructing polymer-based materials with temperature-invariant superelasticity but also holds great promise for extensive applications in ongoing and near-future aerospace exploration.

Valorisation of Agricultural Residue Bio-Mass Date Palm Fibre in Dry-Blended Polycaprolactone (PCL) Bio-Composites for Sustainable Packaging Applications

Abstract Purpose This study experimentally developed and characterised dry-blended Polycaprolactone (PCL)/date palm fibre biodegradable composites for sustainable packaging applications. Date palm fibres are collected from date palm trees as by-products or waste materials. They will be valorised in bio-composite application to promote fibre-based sustainable packaging items over their non-biodegradable synthetic polymer based conventional packaging products. In the dry-blending process, fibre and polymer are mixed with a shear mixer, while, in a melt-blending process, an extruder is used to extrude fibre/polymer blends after applying heating and high shear pressure to melt and mix polymer with fibres. Dry-blending process offers many comparative advantages, such as less equipment, steps, cost, process degradation, energy consumption and hence, lower harmful environmental emissions; while, a proper fibre/polymer mixing is a challenge and it needs to be achieved properly in this process. Therefore, it is important to understand the effects of dry-blending process on manufacturing of PCL/date palm fibre bio-composites for packaging applications, before promoting the dry-blending as a suitable alternative to the melt-blending process. Methods Short chopped fibres were grinded as powders and dry-blended at a ratio of (0 − 10%) (w/w) with PCL polymer using hand and a shear mixer for 30 min, following a compression moulding process to produce bio-composite samples. Tensile, water contact angle, SEM, TGA, DSC and DMA tests and analysis were conducted. The dry-blended PCL/date palm fibre composites’ properties were compared with reported melt-blended samples’ results found in literature. Results Dry-blended samples showed an increase in tensile modulus values (up-to 20%) with fibre inclusion and these values were found close to the melt-blended samples in the literature. Tensile strength and strain values were reduced which could be related to the poor fibre/polymer interface. Fibre addition affected the thermal, thermo-mechanical and crystallisation processes in PCL polymer matrix. Conclusion Dry-blending is capable of producing bio-composites with a very comparable properties to melt-blended counterparts, although a more details study is needed to conduct in future. The results of this study, could be used carefully to design dry-blended PCL/date palm fibre bio-composites for possible packaging applications. The irregular fibre distribution in dry-blended samples could be improved in different ways which should be investigated in future. Graphical Abstract

Fully Bio-Based Polymer Composites: Preparation, Characterization, and LCD 3D Printing.

The present work aimed to prepare novel bio-based composites by adding fillers coming from agro-wastes to an acrylate epoxidized soybean oil (AESO) resin, using liquid crystal display (LCD) 3D printing. Different photocurable formulations were prepared by varying the reactive diluents, iso-bornyl methacrylate (IBOMA) and tetrahydrofurfuryl acrylate (THFA). Then, two fillers derived from different industrial wastes, corn (GTF) and wine (WPL-CF) by-products, were added to the AESO-based formulations to develop polymer composites with improved properties. The printability by LCD of the photocurable formulations was widely studied. Bio-based objects with different geometries were realized, showing printing accuracy, layer adhesion, and accurate details. The thermo-mechanical and mechanical properties of the 3D-printed composites were tested by TGA, DMA, and tensile tests. The results revealed that the agro-wastes' addition led to a remarkable increase in the elastic modulus, tensile strength, and glass transition temperature in the glassy state for the systems containing IBOMA and for flexible structures in the rubbery region for systems containing THFA. AESO-based polymers demonstrated tunable properties, varying from rigid to flexible, in the presence of different diluents and biofillers. This finding paves the way for the use of this kind of composite in applications, such as biomedical for the realization of prostheses.

Novel Organic-Inorganic Nanocomposite Hybrids Based on Bioactive Glass Nanoparticles and Their Enhanced Osteoinductive Properties.

Inorganic-organic hybrid biomaterials have been proposed for bone tissue repair, with improved mechanical flexibility compared with scaffolds fabricated from bioceramics. However, obtaining hybrids with osteoinductive properties equivalent to those of bioceramics is still a challenge. In this work, we present for the first time the synthesis of a class II hybrid modified with bioactive glass nanoparticles (nBGs) with osteoinductive properties. The nanocomposite hybrids were produced by incorporating nBGs in situ into a polytetrahydrofuran (PTHF) and silica (SiO2) hybrid synthesis mixture using a combined sol-gel and cationic polymerization method. nBGs ~80 nm in size were synthesized using the sol-gel technique. The structure, composition, morphology, and mechanical properties of the resulting materials were characterized using ATR-FTIR, 29Si MAS NMR, SEM-EDX, AFM, TGA, DSC, mechanical, and DMA testing. The in vitro bioactivity and degradability of the hybrids were assessed in simulated body fluid (SBF) and PBS, respectively. Cytocompatibility with mesenchymal stem cells was assessed using MTS and cell adhesion assays. Osteogenic differentiation was determined using the alkaline phosphatase activity (ALP), as well as the gene expression of Runx2 and Osterix markers. Hybrids loaded with 5, 10, and 15% of nBGs retained the mechanical flexibility of the PTHF-SiO2 matrix and improved its ability to promote the formation of bone-like apatite in SBF. The nBGs did not impair cell viability, increased the ALP activity, and upregulated the expression of Runx2 and Osterix. These results demonstrate that nBGs are an effective osteoinductive nanoadditive for the production of class II hybrid materials with enhanced properties for bone tissue regeneration.

The enhancement effects of multiple hydrogen bonds between bi-terminal groups and penta-alanine assemblies on creep resistance and mechanical strength of polyisoprene rubbers

Along with the continuously advanced requirements for high performance rubbers such as in aircraft tires, natural rubbers show limitations in achieving high temperature creep resistance and high mechanical strength simultaneously. Meanwhile, the bi-terminal interactions of natural rubber (NR) exhibit unique reinforcement effects, which are difficult to realize in synthetic rubbers. In this article, four different types of bi-terminal polyisoprenes with distinct groups were synthesized, and they were assembled with penta-alanine molecule (5 A) to obtain high-performance rubbers by terminal hydrogen bonding reinforcement. Infrared tests indicate that the strong hydrogen bonds can be formed between two terminals and turn stronger after adding 5 A. Thus, the network of rubbers remains stable under different strains and temperatures and the activation energy of networks is elevated. As a result, this biomimetic design endows polyisoprene with high tensile strength compared with Malaysian NR and greater creep resistance. Further Mooney fitting and DMA test suggests that these confined hydrogen bonds not only increased the number of crosslinking points and entanglements of network, but also are beneficial for the segmental chain motion. In contrast to our common sense on hydrogen bonds which present large relaxation and hysteresis, this study proposes a facile method for preparing high-temperature creep-resistant rubbers by introducing confined hydrogen bonds, which represents a great advance in the structural biomimicry of NR.

A “one‐pot” method for synthesizing zinc tryptophan and its derivatives as highly efficient PVC thermal stabilizer with excellent mechanical properties

AbstractZinc Tryptophan (Trp‐Zn) and zinc N‐(salicylic) tryptophan (SalTrp‐Zn) were synthesized from tryptophan, zinc acetate, and salicylic aldehyde by one‐pot method, respectively. The structure was analyzed by FT‐IR, 1H NMR, and elemental analysis. PVC samples were prepared by stirring method and solvent film process, and then the thermal properties of PVC samples were studied by thermal aging chamber test, Congo red test, electrical conductivity test, and thermogravimetric analysis (TGA). The thermal stability of Trp‐Zn and SalTrp‐Zn stabilized PVC samples was better than calcium and zinc soaps used in industry. The thermal stability time was up to 80 min, and it was a long‐acting thermal stabilizer. After the addition of CaSt2 and Trp‐Zn stabilizer in different proportions, the thermal stability of PVC was obviously improved, and the initial whiteness of the film was improved after the combination of Trp‐Zn/SalTrp‐Zn. In addition, the tensile test verified that the PVC samples stabilized by Trp‐Zn and SalTrp‐Zn had the highest elongation at break. The addition of Trp‐Zn can reduce the elastic modulus of PVC, effectively improve the mechanical properties of PVC, and make the PVC film have better toughness and elasticity. Through DMA and EDS tests, it can be seen that Trp, SalTrp‐Zn had good compatibility with PVC and DOP. The quantum chemical calculation of Trp‐Zn, SalTrp‐Zn and vinyl chloride models was carried out, and the thermal stability mechanism of thermal stabilizer on PVC was analyzed accurately, mainly the absorption mechanism of HCl and the substitution mechanism of unstable chlorine atoms.

Static-dynamic damage mechanism and self-heating effect of a clean elastic polyurethane grouting material for trenchless rehabilitation under high stresses

Compared with traditional excavation rehabilitation, trenchless grouting rehabilitation technology has the advantages of fast, precise, and low-carbon, which has a broad application prospect in wind turbine foundation rehabilitation. In this work, a non-toxic, environment-friendly, fast-setting, high-strength, and high-toughness elastic polyurethane (PU) grouting material was proposed, and the static-dynamic damage mechanism and self-heating effect under high stress were studied by DMA, SEM, static-dynamic compression, and self-heating monitoring tests. The results show that the static compressive properties increased in a power function relationship with increasing strain rate. The dynamic compression fatigue process can be divided into adjustment stage (Stage I), viscoelastic development stage (Stage II) and failure stage (Stage III) or cyclic hardening stage (Stage III*). At 41.57 MPa and 36.95 MPa, fatigue damage parameters increased slowly in Stage I and Stage II, and sharply in Stage III. The stiffness damage, loss factor, cumulative strain, and strain rate increased by more than 100% in Stage III. Fatigue failure dominated by vertical/slanting through-cracks, shed debris, drum deformation, etc. was closely related to temperature and loading. The failure temperature about 59.1 °C, which was higher than the glass transition temperature. At 32.33 MPa, fatigue damage parameters changed slightly and then stabilized, showing exponential relationships with cycles. The max temperatures were less than 15 °C. The slight temperature rise facilitated the adjustment of structure and cyclic hardening under cyclic loading. This work can guide the further engineering application and fatigue durability evaluation of PU grouting materials.

Preparation of a water-based carboxylated Poly(phthalazione ether nitrile) sizing agent for interfacial reinforcement of CF/PPESK composites

This study focuses on synthesizing a range of hydrolysis-modified poly(phthalazione ether nitrile) polymers with different quantities of carboxyl groups (HPPEN-COOH). These polymers are intended to enhance the bonding strength between carbon fibers (CFs) and poly(phthalazine ether sulfone ketone) (PPESK). The chemical structure of HPPEN-COOH was elucidated using FTIR spectroscopy, and the presence of HPPEN-COOH as a coating on the CFs surface was confirmed by XPS analysis. Compared with the UCF/PPESK composite, the interlaminar shear strength of the CF-5/PPESK composite increased by 39 %. In the DMA test, the service temperature and storage modulus of the CF-5/PPESK composite were increased to 268 °C and 112 GPa, respectively. Furthermore, the composite showed satisfactory performance in hydrothermal aging studies. This method is simple and easy to implement, has the potential for large-scale industrial production, and is an environmentally friendly method to improve the interface properties of the CF/PPESK composite.

The Effect of Feeding Sequence on the Structure and Properties of the Ethylene/1-Octene Copolymer in the Semi-Continuous Polymerization Reaction System.

The performance of ethylene/1-octene copolymer primarily depends on the microstructure of the polymer chain. This study employed a new method to control the inter-distribution of hexyl chain branches directly on the backbone of the ethylene/1-octene copolymer. Three ethylene/1-octene copolymers with different inter-distributions of hexyl chain branches were synthesized using [Me2Si(C5Me4) (NtBu)] TiCl2 (Ti-CGC) by different feeding sequences in the semi-continuous polymerization reaction system. The three copolymers were named according to the feeding sequence of the materials: ethylene/1-octene/Ti-CGC (EOC), 1-octene/Ti-CGC/ethylene (OCE), and ethylene/Ti-CGC/1-octene (ECO), respectively. The structure and properties of the copolymers were characterized using HT-GPC, 13C-NMR, DSC, WAXD, DMA, MI, and Uniaxial Tension Test. The results showed that the feeding sequence greatly affected the comonomer distribution of the molecular chains, molecular weight, molecular weight distribution, and chemical composition of the copolymers, consequently influencing their thermal performance and mechanical properties. Thus, it is probable that one could obtain an ethylene/1-octene copolymer with designed properties by controlling the feeding sequence during the ethylene/1-octene semi-continuous copolymerization process.

Adhesion of Historic Tile Fragments in Outdoor Architectural Settings

Azulejos are part of Portugal’s most important cultural heritage. However, a large part of this heritage is at risk due to lack of or improper conservation treatments. There are, however, not many studies dedicated to the procedures and materials used in their conservation to guide the choices of conservators/restorers. Through this work, the performances of the adhesives commonly used in azulejo conservation are studied considering the extreme conditions they may experience when in an outdoor environment. Three types of adhesives were studied: acrylics, epoxies, and cellulose nitrates. The adhesives were evaluated for their workability and characterized by FTIR, DMA, and bending tests to obtain information on their adhesion effectiveness and compatibility with the azulejo ceramic substrate before and after artificial and natural ageing. When subjected to mechanical loads, the high strength and stiffness of the epoxy resins could lead to the development of new fractures in the previously undamaged ceramic matrix, making them less suitable for the adhesion of historic tile fragments. Cellulose nitrates revealed a high chemical alteration and the highest degradation rate in the mechanical properties with ageing, showing it to be the least stable in the studied conditions. The acrylic resins proved to be the most chemically stable, with less yellowing and with physical properties that revealed to be the most compatible for the adhesion of the studied azulejo fragments in outdoor environments.

Redox cationic frontal polymerization: a rapid curing approach for carbon fiber-reinforced composites with high fiber content

Conventional frontal polymerization processes for epoxy-based composites rely on cations and radicals generated by a short (and local) light or heat stimulus in the presence of an iodonium salt and a radical thermal initiator. However, due to heat losses, the propagation of the exothermic curing front is often limited by sample geometry and filler concentration. Redox cationic frontal polymerization (RCFP) is a promising approach to radically expand the composition and design options of frontally cured epoxy-based composites. By adding stannous octoate as reducing agent, a higher number of radicals and cations are generated at lower temperature, which yields highly cured composite even at elevated filler content. In the current study, RCFP was used to cure standard unidirectional carbon fiber-reinforced composites based on a commercially available epoxy resin and the properties were compared with its anhydride hardener-cured counterpart. Cure degree and thermal properties of the resins were determined by ATR FT-IR spectroscopy and DMA analysis. Subsequently, unidirectional composites with a fiber volume content of ~ 60% were produced via vacuum infusion and subjected to DMA, tensile, compression, and inter-laminar shear tests. The results showed a remarkable similarity between mechanical properties of RCFP and anhydride hardener-cured composites. The RCFP-cured composites exhibited even a higher damping resistance and compression strength than anhydride hardener-cured composites. The results show that RCFP allows for a significant reduction in the curing time (from several hours to 60 min), while it yields composites with properties comparable to classic anhydride-cured systems.Graphical abstract