Dynamic Thermomechanical Analysis Research Articles

Comparative study of the kinetic behaviors and properties of aromatic and aliphatic bismaleimides

In this paper, three aromatic bismaleimides (BMI-70, BMI-DE and BMI-80) and two aliphatic bismaleimides (BMI-DDA and BMI-C36) were synthesized. The structures were characterized using nuclear magnetic resonance (NMR) spectra and Fourier transform infrared (FT-IR) spectra. Their polymerization behaviors were discussed by non-isothermal differential scanning calorimetry (DSC). The thermal and dielectric properties of the poly(bismaleimide) were investigated using thermogravimetric analysis (TGA), dynamic thermo-mechanical analysis (DMA), and an impedance analyzer. The results indicate that the aliphatic bismaleimides exhibit lower apparent activation energies and dielectric properties, with BMI-DDA displaying an average activation energy of 105.5 kJ mol−1 and the dielectric constant of P(BMI-C36) is 2.558 @ 10 MHz. The aromatic polybismaleimides possessed better thermal stability, among which, the 5 % thermal decomposition temperature (Td,5) of P(BMI-70) was 513.5 °C, and the residual carbon rate at 800 °C was 44.6 %. In additional, water absorption was studied and their saturated water absorption was less than 4 %.

Enhancing mechanical properties of polyvinyl chloride: Novel organic‐modified cinnamate‐intercalated calcium aluminum hydrotalcite as a high‐efficiency thermal stabilizer

AbstractTo make the hydrotalcite uniformly dispersed in polyvinyl chloride (PVC) and enhance its thermal stability, cinnamate‐intercalated calcium aluminum hydrotalcite (CaAl‐cinnamate‐LDHs) underwent organic modification with cetyltrimethylammonium bromide/sodium dodecyl sulfate/polyethylene glycol (CTAB/SDS/PEG). The structures of modified hydrotalcite were characterized using x‐ray diffractometer, scanning electron microscope, particle size analysis, and water contact angle test. The thermal stability was assessed through thermal aging oven experiment, Congo Red experiment, and thermogravimetric experiment, revealing their exceptional performance. Simultaneously, the synergistic effect of PEG‐LDHs with auxiliary thermal stabilizers was examined, with epoxy soybean oil proving to be the most effective, which made the PVC sample incompletely black within 120 min. Mechanical properties and dynamic thermomechanical analysis indicated that the overall mechanical characteristics of the PVC samples with modified hydrotalcite were significantly superior to the unmodified CaAl‐cinnamate‐LDHs. Additionally, the optical performance test demonstrated excellent transparency in the PEG‐LDHs/PVC sample. Through analyzing the thermal stability mechanism, it was indicated that hydrotalcite effectively absorbed HCl. Furthermore, the combination of PEG‐LDHs and ESO replaced unstable Cl atoms and reacted with conjugated double bonds, thereby reducing the aging and discoloration of PVC.Highlights The modified hydrotalcite preparation process was simple and easy to operate. The CTAB/SDS/PEG‐LDHs/PVC samples exhibited excellent thermal stability. Mechanical properties of the PVC samples with modified hydrotalcite were significantly superior to the unmodified CaAl‐cinnamate‐LDHs.

Investigating the Effect of ABS on the Mechanical Properties, Morphology, Printability, and 4D Printing of PETG‐ABS Blends

AbstractIn this study, Acrylonitrile butadiene styrene (ABS) with three different ratios of 30%, 50%, and 70% is used to enhance the shape memory and mechanical properties of Polyethylene terephthalate glycol (PETG). Additionally, morphology, printability, and dynamic thermomechanical analysis are also examined. The thermal test results show that PETG‐ABS compounds have two transition temperatures in the range of 80 and 110 °C, which are related to the components. By changing the weight percentage of PETG from 30 to 70%, three morphologies of matrix‐droplet, sea‐island, and combination of co‐continuous and matrix‐droplet are observed. The results of the mechanical properties show an increase in strength with the increase of ABS, which can be justified due to the higher strength of ABS compared to PETG. The highest tensile strength of 32.48 MPa and 15.16% elongation is obtained for PETG‐ABS(30‐70) and PETG‐ABS(70‐30), respectively. Due to the better shape memory performance of PETG, PETG‐ABS(50‐50) and PETG‐ABS(70‐30) have complete shape recovery, and with the increase of PETG, the shape recovery rate also increased. This diversity in morphology, mechanical properties, and shape memory effect is one of the goals of this research which is well fulfilled.

Tunable structure and linear viscoelastic properties of poly(glycerol adipate urethane)-based elastomeric composites for tissue regeneration

Elastomeric biocomposites based on poly(glycerol adipate urethane) and hydroxyapatite were fabricated for tissue regeneration. The poly(glycerol adipate urethane) (PGAU) elastomeric composite matrices were obtained by chemical crosslinking of the poly(glycerol adipate) prepolymer (pPGA) with diisocyanate derivative of L-lysine. Two series of composites varying in the amount of L-lysine diisocyanate ethyl ester (LDI) used as a crosslinking agent were manufactured. As a ceramic filler both unmodified and L-lysine surface-modified hydroxyapatite (HAP) particles were used. The novelty of our research consists in the manufactured elastomeric materials and characterization of their linear viscoelastic (LVE) properties. The LVE properties of the composites were investigated by means of dynamic thermomechanical analysis. Frequency sweep and amplitude sweep measurements were performed in shear mode. The influence of the crosslinking agent (LDI) amount, HAP content and surface modification of HAP on the LVE properties of the composites was determined based on the analysis of the master curves of storage (G′) and loss (G″) moduli and of tanδ of the composites. Depending on the amount of LDI, HAP and surface modification, the materials differ in the values of rubber elasticity plateau modulus (G0) and G′ and G″ determined at selected shear frequencies and at the glassy state. G0 ranges from 278 kPa to 3.98 MPa, G′ in the glassy state is within the range of 219 MPa–459 MPa. The G0 values of the PGAU-based composites are within the stiffness range of soft tissue. In view of the choice of HAP as the ceramic component and the G0 values, elastomeric composites have the potential to be used as filling materials in small bone defects (due to their mechanical similarity to osteoid) as well as materials for cartilage tissue regeneration.

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.

Composite embedded track structure considering temperature dependent characteristics for rolling noise reduction of inter-city railway system

Intercity railway will generate strong noise when passing through the surrounding residents, among which rolling noise is the main noise source and is difficult to control. A composite embedded track structure containing polymer material was fabricated to analyze its damping and rolling noise reduction characteristics. The damping characteristics of polymer materials of embedded track were tested by dynamic thermo-mechanical analyzer (DMA Q800). The frequency response function (FRF) of the embedded track system is tested by force hammer percussion method. The vibration of the embedded track is simulated by the the 2.5-dimensional finite element method (2.5D FEM) considering damping characteristics obtained by material test of DMA Q800. The sound radiation model of embedded track is developed by using 2.5-dimensional sound boundary element method (2.5D BEM). The model is verified by the test. The FRF, track decay rate, and wheel-rail force at different temperatures are analyzed. With the decrease of temperature, the elastic modulus and loss factor of polymer material of embedded track increase, which will affect the above results. Sound directivity and effect on wheel-rail noise reduction of embedded track have been studied. The results show that the composite embedded track has good damping characteristics and noise reduction performance. Sound sensitivity analysis of loss factors of the three polymer materials of embedded track is carried out to improve embedded track noise reduction capability.

Study on mechanical properties of vacuum‐infused glass fiber reinforced thermoplastic methacrylic resin composites

AbstractIn recent years, the growing environmental awareness has prompted increased attention towards the substitution of nonrecyclable thermosetting epoxy resin composite materials with recyclable thermoplastic composite materials. The objective of this study is to utilize a laboratory‐made polymethyl methacrylate (PMMA)/methyl methacrylate (MMA) binary liquid resin (PMBLR) to prepare thermoplastic resin/glass fiber (GF) composite materials using the vacuum‐assisted perfusion method. These composites are then compared with GF‐reinforced thermosetting epoxy resin composites. The investigation reveals a significant influence of benzoyl peroxide (BPO) content on the mechanical properties of pure MMA and PMBLR casting resins, which also incorporate N‐methyl‐N‐((1‐methyl‐1H‐indol‐3‐yl) methyl) aniline (DMA) as redox composite initiators. The optimal mechanical properties for both types of casting resins are achieved at a DMA:BPO:MMA ratio of 0.5:1.2:100. Additionally, at a PMMA concentration of 24 wt% in PMBLR under this specific initiator ratio, the composites demonstrate the most desirable properties. Furthermore, a comparative analysis of PMBLR/GF composites and epoxy/GF composites indicates that the former exhibit superior 90° tensile strength, bending strength, and short beam shear strength. The fracture morphology analysis highlights discernible micro‐ductile fracture characteristics in PMBLR/GF composites, distinguishing them from epoxy/GF composites. Dynamic thermomechanical analysis (DMA) results further reveal a higher storage modulus and loss factor in PMBLR/GF composites when compared to epoxy/GF composites.Highlights Glass fiber‐reinforced composites were fabricated at ambient temperature. A degradable PMMA/MMA binary thermoplastic resin (PMBLR) was developed as a replacement for non‐degradable epoxy. PMBLR composites exhibit enhanced strength compared to epoxy: tensile (+18.8%), bending (+27.4%), and short beam shear (+34.3%).

Preparation and Properties of Polyvinyl Alcohol (PVA) Composite Films by Incorporation of Octadecylamine Polyoxyethylene Ether Modified Carbon Black Particles as Filler

In our research described here, a strong acid oxidizing agent was selected to modify the surface of carbon black (CB) to obtain oxidized carbon black (OCB) particles. These OCB particles were then subjected to an ionic bonding reaction with alkaline amine groups present on the surface of octadecylamine polyoxyethylene ether (AC1830) in the form of a paste, resulting in the production of polyether amine-modified oxidized carbon black particles (A-CB). FTIR confirmed the successful production of the A-CB particles. The PVA composite films were prepared using the casting method with varying amounts of A-CB as filler and PVA as the matrix. The films were then analyzed using tensile, scanning electron microscopy, dynamic thermo-mechanical analysis, DSC, and water absorption testing. The results showed that the tensile strength was highest at 3% A-CB, reaching 154.85 MPa. A-CB was well dispersed in PVA at low contents (1% and 3%). The loss modulus, energy storage modulus, crystallinity, and crystallization rate of the A-CB/PVA films improved compared to PVA films. Additionally, the issue of excessive water absorption in A-CB/PVA has been improved.

Preparation and properties of recycled polypropylene‐based wood–plastic composites reinforced with a bio‐based compatibilizer

AbstractWood‐plastic composites are green composites made of plastic as the matrix and wood as the filler; however, the incompatibility between these two leads to the degradation of the composites. This paper reports the synthesis of a novel bio‐based compatibilizer, annotated as OA‐g‐H20, by grafting oleic acid (OA) on a hyperbranched polyester (Boltorn H20). The effect of modifying recycled polypropylene‐based wood–plastic composites with this compatibilizer was then assessed. The Fourier transform infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography techniques were employed to characterize the fabricated OA‐g‐H20, while its modification effect was assessed by differential scanning calorimetry, dynamic thermomechanical analysis, scanning electron microscopy, and mechanical property tests. The experimental results revealed that the optimal addition amount of OA‐g‐H20 was 2.0 wt.%.Highlights A new bio‐based compatibilizer, OA‐g‐H20, for wood–plastic composites is reported. OA‐g‐H20 was obtained by grafting oleic acid on a hyperbranched polyester (H20). OA‐g‐H20 provided good mechanical reinforcement for the wood–plastic composites. OA‐g‐H20 improved the crystallinity of the composites. The reinforcement mechanism of OA‐g‐H20 in wood–plastic composites is elucidated.

Dynamic characteristics of bladder type attenuator for hydraulic systems

Flow ripples caused by the pump will lead to system failure or equipment damage. The bladder type attenuator is utilised to suppress flow ripples in piping systems, though its mathematic model has not been given out precisely. In this paper, the governing equations of the hollow cylindrical shell describing the bladder’s behaviour are studied. Considering the bladder’s viscoelastic materials, the constitutive function is obtained through DMA (Dynamic thermo-mechanical analysis) test and the WLF (Williams–Landel–Ferry) equation. Thus, the dynamic model of the attenuator can be written as an impedance expression, which consists of integral, fractional, constant, and differential components. Three experiments are carried out to validate the theoretical models. The static and dynamic models of the bladder are validated by experiments, indicating good agreement. The impedance model of the attenuator is validated by a hydraulic experiment assessed with the IL (insertion loss) index, showing high accuracy. All models proposed in this work are proven to be effective and accurate, and can be used to evaluate and optimise the bladder type attenuator theoretically.

Influence of Photoinitiator Type and Curing Conditions on the Photocuring of Soft Polymer Network

The presented work deals with the photocuring of telechelic macromonomers derived from plant-based fatty acids to obtain a soft polymer network. Compositions were made by mixing macromonomers with three different concentrations (0.5, 1, and 2%) of two type I photoinitiators (Omnirad 2022 and Omnirad 819). All formulations were then subjected to photopolymerization studies by applying UV-assisted differential scanning calorimetry (UV-DSC) measurements at isothermal conditions at 37 °C with a narrow light source wavelength of 365 nm and irradiation (light intensity) of 20 and 50 mW/cm2. The percentage conversions, reaction orders, and constants were estimated based on autocatalytic Sestak–Berggen and Avrami models. In this work, for the first time, the influence of the curing conditions on the photopolymerization process, such as the photoinitiator concentration, light intensity, and oxygen presence/absence, were investigated for these novel systems. The results indicated significant differences between the two commercially available photoinitiators and their effects on photopolymerization kinetics. The maximum reaction rate was found to be considerably higher for Omnirad 2022 (which is a blend of three different compounds), especially at a lower light intensity, i.e., 20 mW/cm2, compared to Omnirad 819. However, it led to lower maximum conversion in an air atmosphere. The dynamic thermomechanical analysis (DMTA) revealed that light intensity, photoinitiator concentration, and oxygen presence had a strong effect on the storage modulus and loss modulus values. It was concluded that the chemical structure of the photoinitiator and curing conditions had a strong effect on the photopolymerization kinetics and properties of the prepared soft polymer networks.

Dynamic properties of butadiene styrene rubbers with layered silicates

In our study, modification of SBR-1705 butadiene styrene latex using a variety of bentonite clay variants was carried out Among them were domestic sodium bentonite, domestic bentonite pretreated with surfactants (surfactants), as well as organoclays based on foreign layered silicates and also treated with surfactants at the coagulation stage with subsequent rubber release. Further, within the framework of our study, we carried out a detailed comparative study of physical and mechanical properties of rubbers produced using modified butadiene-styrene rubbers. We considered rubbers containing different variants of bentonite, including both domestic origin and imported bentonite. The dynamic properties of these rubbers, including elastic modulus and mechanical loss angle tangent, were analyzed using dynamic thermomechanical analysis (DTMA). The study found that the rubber samples containing PT clay and Cloisite 30B showed a 20% reduction in mechanical loss tangent within the operating temperature range. This indicates an improvement in the mechanical properties of the rubber under a variety of operating conditions. In addition, rubber samples containing imported layered silicates and treated with surfactants exhibited increased strength both before and after thermo-oxidative aging at 150°C. These results emphasize the importance of silicate and surfactant composition selection in developing rubbers with improved mechanical properties and durability. The findings of this study have important implications for industry and academia, emphasizing the role of proper bentonite selection and processing in creating rubbers with optimal performance for a variety of applications

Dynamic thermomechanical analysis on stiffened composite plates with damage

The dynamic thermomechanical analysis on stiffened composite plates with damages are investigated in this article based on the extended layerwise method (XLWM) and three-dimensional finite elements method; a thermomechanical extended-layerwise/Solid-element method (TELW/SE) is established. In TELW/SE, the thermomechanical extended-layerwise method (TELW) and thermomechanical three-dimensional solid elements are used to simulate plate and stiffeners, respectively. The final governing equations are assembled by using the interface conditions to ensure the compatibility of displacements and temperature, together with the internal force equilibrium. Several typical damages in stiffened composite plates can be described accurately in the proposed method, such as delamination, transverse crack and stiffener/plate interface debonding.

Flexible fabrication of a novel SiO2/AF/ZIF-L composite embedded with MOF structure and its thermal insulation properties

ZIF-L, a metal-organic framework (MOF) material, has a two-dimensional (2D) foliation, a large specific surface area, excellent thermal stability and CO2 adsorption performance, respectively. In this work, in order to further improve the thermal insulation performance of SiO2 aerogel composite fabrics, ZIF-L powder was first prepared as a reinforcing particle, and then added to silica aerogel. Finally, SiO2/AF/ZIF-L composites were obtained by solution impregnation method. The influence of different ZIF-L concentrations on the insulation performance of composites and their influencing factors were studied. Furthermore, these composites were fully characterized using BET measurement, Instron 5967, precision transient thermal performance tester, infrared thermal imager, insulation performance test, thermogravimetric analyzer, and dynamic thermomechanical analyzer. The results showed that 0.12% SiO2/AF/ZIF-L composites had excellent thermal insulation performance, with a thermal conductivity as low as 0.029 W/(m·K). In addition, SiO2/AF/ZIF-L composites fabricated by atmospheric drying method had the best thermal insulation performance under the conditions of gel time of 24 h, hydrolysis time of 5 h, and polycondensation pH value of 5–6.

Near-Infrared Light Triggered the Shape Memory Behavior of Polydopamine-Nanoparticle-Filled Epoxy Acrylate.

Through the effective combination of photothermal conversion agent polydopamine (PDA) nanoparticles and epoxy acrylate polymer (EA), a new kind of near-infrared (NIR) light-triggered shape memory polymer (PDA/EA) is developed. Due to the outstanding photothermal effect of PDA, even with a very low concentration of PDA (0.1 wt.%), when exposed to an 808 nm NIR light with a power of 1 W/cm2, the temporary shapes can be fully light-responsive, recovered in 60 s. Based on dynamic thermomechanical analysis and thermal gravimetric analysis, it can be seen that the introduction of PDA is beneficial for improving dynamic mechanical properties and thermal resistance compared to EA. As an environmentally friendly and highly efficient photoactive SMP, PDA/EA has a great application prospect.

The effect of Al/oxidizers interfacial structure on the mechanical properties of composite propellants

In this paper, the mechanical properties of a typical four-component composite solid propellants with various designed Al/oxidizer interfaces have been studied. The Al/oxidizer interfacial control is mainly realized by using the core-shell composites AP@Al and Al@RDX with different particle sizes, where Al powder was coated with a thin layer of polydopamine (PDA) as the binding sites, so that the oxidizers could crystalize on it during a rapid spray granulation process. The stress-strain curves of the above propellants at different temperatures and different tensile rates have been obtained. The dependence of the loss factor on temperature was studied by using a dynamic thermomechanical analysis (DMA). It has been shown that the fracture elongation of the interfacial modified propellants can reach 51.81% at room temperature, which is 127.3% higher than that of the blank formulation under the same formulation. Moreover, the temperature and strain rate sensitivity of interfacial controlled HTPB propellants is much less than that of traditional ones. The microstructure of these propellants at the crack sites was investigated by scanning electron microscopy (SEM) supported with micro-area in-situ tensile CT scanning technology, to clarify their damage and failure mechanisms.

Characterization of the alkali-induced protein cross-linking in buckwheat sourdough steamed bread

This study elucidated the alkali-induced protein cross-linking behaviors of buckwheat sourdough steamed bread (BSSB). When the alkali concentration increased to 1.5% (on a total flour weight basis), the protein extractability in sodium dodecyl sulfate (SDS) decreased by 2.29% while the disulfide (SS) bond content increased by 5.97 μmol/g protein, indicating that the alkali promoted the SS cross-linking of the proteins. The formation of dehydroalanine (DHA) and lanthionine (LAN) at alkali concentrations of 2.0% and 2.5% demonstrated the occurrence of DHA-derived cross-linking. To explore the role of SS cross-linking in the quality of BSSB, the thiol-blocking agent N-ethylmaleimide (NEM) was also employed. It was determined that the BSSB with NEM had almost no gas cells and that the specific volume was 48.41% lower than the control. The alkali increased the specific volume by up to 26.75% at 2.0% concentration and ameliorated the crumb structure of the BSSB. Dynamic thermo-mechanical analysis revealed that the alkali also delayed the starch gelatinization and gas cell opening, which may have contributed to the gas holding capacity of the BSSB. The amino acid residues involved in the DHA-derived cross-linking and the potential cross-linking sites were identified via liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. It was found that both the Cys197 from wheat peroxidase and the Cys105 from the wheat alpha-amylase/trypsin inhibitor CM16 were crucial to the formation of the DHA-derived cross-links and that the LAN between two cysteines was inter-chain.

Thermal Properties of Kenaf Fiber Reinforced Polyamide 6 Composites by Melt Processing

In recent years, there has been much effort to find cost-effective ways to replace petroleum-based commodity plastics with biodegradable polymers with comparable thermal characteristics. The 5 wt.%, 10 wt.%, and 15 wt.% kenaf fiber were melted, and blended with polyamide-6 via a Brabender mixer, followed by compression molding. To evaluate the thermal properties of composites, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic thermomechanical analysis (DMA) were conducted. According to the TGA results, increased kenaf fiber contents decreased the composite’s thermal stability. Neat PA6 matrix decomposed rapidly at 425°C, which was comparatively higher than PA6 composites. From the DSC analysis, the addition of natural fibers resulted in quantified changes in the glass transition temperature (T<sub>g</sub>), melting temperature (T<sub>m</sub>), and crystallization temperature (T<sub>c</sub>) of the PA6 composites. According to the DMA, the storage modulus of neat PA6 was 1177 MPa and decreased to 1076 MPa for 5 wt% of kenaf fiber in PA6 composite. The Kenaf fiber/polyamide 6 composites appeared to have lower thermal stability than neat PA6. This study demonstrated that the kenaf fiber/polyamide 6 composites were successfully prepared, and a detailed thermal analysis was conducted. Improving the KF/PA6 composites can be further studied to increase thermal stability.

The Mechanical Properties of Silicone Rubber Composites with Shear Thickening Fluid Microcapsules.

In this study, Sylgard 184 silicone rubber (SylSR) matrix composites with shear thickening fluid (STF) microcapsules (SylSR/STF) were fabricated. Their mechanical behaviors were characterized by dynamic thermo-mechanical analysis (DMA) and quasi-static compression. Their damping properties increased with the addition ofSTF into the SR in DMA tests and the SylSR/STF composites presented decreased stiffness and an obvious positive strain rate effect in the quasi-static compression test. Moreover, the impact resistance behavior of the SylSR/STF composites was tested by the drop hammer impact test. The addition of STF enhanced the impact protective performance of silicone rubber, and the impact resistance increased with the increase of STF content, which should be ascribed to the shear thickening and energy absorption of STF microcapsules in the composites. Meanwhile, in another matrix, hot vulcanized silicone rubber (HTVSR) with a mechanical strength higher than Sylgard 184, the impact resistance capacity of its composite with STF (HTVSR/STF) was also examined by the drop hammer impact test. It is interesting to note that the strength of the SR matrix obviously influenced the enhancement effect of STF on the impact resistance of SR. The stronger the strength of SR, the better the effect of STF on improving the impact protective performance of SR. This study not only provides a new method for packaging STF and improving the impact resistance behavior of SR, but is also beneficial for the design of STF-related protective functional materials and structures.

Construction of novel Cu-α-diimide interactions for enhancing thermal resistance and dimensional stability of polyimide films

The new-generation polyimide films with simultaneously outstanding thermal stability and low coefficient of linear thermal expansion (CTE) are urgently needed. Herein, coordination bonds were employed to improve polyimide films' heat resistance and dimensional stability. Polyimide-Cu complex films were fabricated by incorporating α-diimide units (bidentate ligands) into the BPDA-ODA (the structure of commercially available Upilex-R® polyimide films) backbones. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Energy dispersive X-ray mapping results showed that the coordination interactions occur between α-diimide and copper ions. Wide-angle X-ray diffraction (WAXD) and two-dimensional small-angle X-ray scattering (SAXS) spectra demonstrated that Cu-α-diimide coordination structures introduced in intermolecular chains leading polyimide films transformed from a semi-crystalline state to amorphous state, and inhibited the long-period formation structures. The plateau modulus and longer characteristic relaxation time (τ∗ = 1996.5 s) revealed by dynamic thermomechanical analysis indicated that crosslink networks were successfully formed by constructing coordination bonds. As a result, polyimide films' thermal resistance and dimensional stability were simultaneously enhanced. The typical PI-Cu50 films exhibited elevated glass transition temperatures of 353 °C (pristine PI-Cu0 ∼ 302 °C) and a lower CTE of 47.4 ppm/K (pristine PI-Cu0 films ∼ 64.4 ppm/K) in ranges of 300–400 °C, showing a promising application in the field of high-temperature environments.