Hot-pressed Films Research Articles

Towards a scalable production of β-Li3PS4-based all-solid-state batteries: Optimizing pressing parameters of the tape-casted solid electrolyte and composite cathode films

Pressing of all-solid-state batteries (ASSBs) components is one of the most important processes for scalable production. Henceforth, pressing parameters (pressure and temperature) for β-Li3PS4 (β-LPS) solid electrolyte (SE) separator films and LiNi0.6Co0.2Mn0.2 (NCM622)/β-LPS composite cathode films prepared by a slurry-based process were investigated and optimized. Compression of the β-LPS film at a temperature of 100 °C led to higher ionic conductivity than cold-pressed films. Raman and X-ray photoelectron spectroscopic analyses revealed no changes in the chemical nature of β-LPS material after hot pressing. Interestingly, time-of-flight secondary ion mass spectrometric (ToF-SIMS) analyses indicated a binder enrichment in the upper layers of the hot-pressed film. In a similar trend, increasing compression and temperature resulted in higher densification of NCM622/β-LPS composite cathode films. Based on galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) measurements, hot-pressed composite cathode at 200 MPa/100 °C exhibited a higher coverage percent of catholyte on cathode active material and a greater Li+ diffusion coefficient (DLi+) than cold-pressed one at 200 MPa/20 °C. Cycling tests of “Li–In│β-LPS│NCM/β-LPS” ASSBs with hot-pressed films displayed better cycling performance than that with cold-pressed ones, attributed to the higher concentration of electrochemically active NCM in close contact with β-LPS catholyte.

An investigation of novel biodegradable flexible copolyester derived from bio-based isosorbide: Synthesis and characterization of poly(butylene-co-isosorbide sebacate)

A series of fully bio-based poly(butylene-co-isosorbide sebacate) (PBISe) copolyesters are synthesized from sebacic acid (Se), 1,4-butanediol (BDO), and isosorbide (IS) via a two-step melt polycondensation method. The synthesized PBISe copolyesters are characterized using various techniques, including 1H NMR spectroscopy; GPC; FT-IR spectroscopy; HR-XRD; DSC; TGA; transparency, tensile, and tear strength testing; and rheological property analysis. The Mw and Mn values of the PBISe copolyesters are 126,000–148,000 and 50,000–63,500, respectively. The introduction of the rigid, bulky, and asymmetric IS unit disrupts the regularity and mobility of the polymer chain, resulting in a nearly linear reduction of the melting temperature, enthalpy, and crystallinity, from 66 to 42 °C, 81 to 37 J/g, and 41.4 to 19.0%, respectively, with an increase in the IS content from 0 to 30 mol% relative to the total diol concentration. The reduction of crystallinity without the formation of new crystal planes with the poly(butylene sebacate (PBSe) copolyester containing 30 mol% IS resulted in improved transparency (73.8% transmittance at 600 nm). Additionally, the PBISe copolyesters exhibit Tonset and Tmax in excess of 405 °C and 425 °C, respectively, as well as shear-thinning and viscous melt-flow behaviors, making them suitable for melt processing. The tensile strength and elongation at break of the hot-pressed films of the IS-added PBISe copolyesters with ≤16% content are 31.6–36.3 MPa and 639.2–809.9%, respectively. The developed PBISe copolyesters have great potential as bio-based, biodegradable, and flexible materials for packaging and coating applications with low processing temperatures.

Colloidal Photonic Composites with a Long-Range Order by Hot-Pressing Polymer Brush-Grafted Silica Colloids.

Colloidal photonic composites (CPCs) are unique optical materials that combine flexible and responsive polymers with colloidal photonic crystals, and they have promising applications in colorful displays, optical anticounterfeiting, and visual sensors. However, conventional self-assembly strategies for constructing CPCs via solvent evaporation have faced limitations due to the meticulous regulation required during the evaporation process and typically long preparation durations. Here, we present an external force method to achieve a long-range ordered arrangement in CPCs by hot-pressing poly(2-[[(butylamino)carbonyl]oxy]ethyl acrylate (PBCOE)) brush-grafted silica colloidal particles (SiO2-g-PBCOE). We show that the hot-pressing conditions (i.e., temperature and pressure) and the silica volume fraction (φsilica) of the SiO2-g-PBCOE colloidal particles play crucial roles in determining their ordering and optical properties. By optimization of the hot-pressing temperature up to 100 °C and pressure of 5 MPa, a long-range ordered arrangement of SiO2-g-PBCOE colloidal particles with a φsilica of 20.3% can be achieved. For the effect of structural features, our findings reveal that SiO2-g-PBCOE colloidal particles featuring a higher φsilica are more prone to obtain a long-range ordered arrangement compared to a lower φsilica under hot-pressing conditions at relatively low temperature and pressure (50 °C and 5 MPa), which is mainly attributed to the chain entanglement and hydrogen bonding interactions induced by grafted longer polymer brushes, leading to additional energy inputs and weakening the ordering. Significantly, the critical φsilica (φc) of SiO2-g-PBCOE colloidal particles is discerned, strongly influencing the optical properties of the hot-pressed films. Specifically, a hot-pressed SiO2-g-PBCOE film with a critical φsilica of 29.3% displays enhanced optical properties characterized by intensified reflection peaks, narrowed full width at half-maximum (FWHM), and brilliant structural colors. Notably, in this work, we reveal the mechanism of hot-pressing-driven core-shell colloidal particle ordering and the key factors affecting the ordering of colloidal particles, i.e., chain entanglement and hydrogen-bonding interactions, which play a crucial role in obtaining CPCs with controllable structures. Moreover, angle-dependent structural color is observed in the hot-pressed SiO2-g-PBCOE film with a φsilica content of 29.3% due to the unique attributes of the highly ordered arrangement, while the films exhibit mechanochromic properties due to chain entanglement and hydrogen bonding interactions. This work provides valuable insights into the rapid construction of highly ordered CPCs and establishes a solid foundation for external force-assisted ordering of colloidal particles.

Effect of Hot Pressing on the Optical, Thermal, and Dielectric Properties of Solution Cast Prepared Nanocomposite Films Based on a Poly(Vinylidene Fluoride-co-Hexafluoropropylene) and Poly(Ethylene Oxide) Blend Matrix with Dispersed Zinc Oxide Nanoparticles

In our research described herein, the hot pressing treatment at 90 °C under 2 tons of pressure on solution cast polymer nanocomposite (PNC) films based on a host matrix of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and poly(ethylene oxide) (PEO) with varying polymer blend compositions (20, 50, and 80 wt% P(VDF-HFP) or PEO) and 2 wt% zinc oxide (ZnO) nanofiller, was performed; the effects of this treatment and the composition variations on the optical, thermal, and dielectric properties was explored. The ultraviolet-visible wavelength range study revealed slightly reduced absorbance and a little increased energy band gap after the hot pressing of the nanocomposite films. Differential scanning calorimetry of the solution cast-hot pressed (SC-HP) PNC films explained the reduced thermal stability of the poly(ethylene oxide) crystallites and also the degree of crystallinity. The broadband dielectric measurements of these materials, at 27 °C, confirmed significant changes in various dielectric polarization processes, demonstrating a large redistribution of constituent interfaces by the hot press treatment. Additionally, the 90 °C hot pressed PNC film of equal polymer compositional ratio was further hot pressed at 130 °C and 160 °C, step by step, and characterized to examine the variations in dielectric properties. The properties of these thermally treated composite films are discussed concerning their use for flexible device applications.

A new strategy to prepare high-performance copper azide film for micro-initiator.

Copper azide (CA) has gradually become the chosen priming agent for microexplosive devices as a lead-free green priming agent. However, charge loading is challenging due to its high electrostatic sensitivity, severely limiting its practical application. In this study, copper hydroxide particles were evenly coated on the surface of carbon fiber using electrospinning and quick hot-pressing, and CA-based composites with uniform load were created using the in-situ azide technique while keeping good film characteristics. The produced CA-HP film has an electroostatic sensitivity of 3.8 mJ, which is much higher than the raw material of 0.05 mJ. The flame sensitivity has also been increased from 45 cm to 51 cm, and the use safety has been considerably enhanced. Furthermore, hot-pressed CA-HP films can improve the film's qualities, such as easy cutting and processing into the required shape, compatibility with MEMS processes, and the ability to successfully detonate secondary explosives with only 1 mg. This novel coupling technology expands the possibilities for developing high-safety primers for micro-initiator.

Orientation and Grain Size in MAPbI3 Thin Films: Influence on Phase Transition, Disorder, and Defects

In recent years, record efficiencies of halide perovskite-based devices have been achieved by processing high-quality thin films, where small morphology differences seem to be relevant for optimized optoelectronic functionality. However, a detailed understanding on how small morphological changes in perovskite films affect their structural and optoelectronic properties is still missing. Here, we investigate the influence of small morphology differences (i.e., increased grain size and crystallographic orientation), which are induced by hot-pressing methylammonium lead iodide (MAPbI3) thin films, on the structural properties, phase transition behavior, energetic disorder, and defects. To this end, detailed temperature-dependent photoluminescence (PL) and absorption analyses from 300 K down to 5 K are performed. The morphology differences, confirmed by scanning electron microscopy and X-ray diffractometry analyses, result in an increased phase transition temperature for hot-pressed (HP) films, which we attribute to less strain. Moreover, fluence-dependent and transient PL measurements reveal a lower defect density in HP films. Here, besides grain size, also the degree of orientation appears to enhance the charge carrier lifetimes. The identified interdependence of strain and defect properties with film morphology suggests small differences in the perovskite’s energetic disorder. Our work thus emphasizes the importance that even small structural differences in halide perovskites have on their optoelectronic functionality, spurring their further optimization.

Controlled Allocation of Aromatic/Aliphatic Substituents to Polysaccharides and Lignin in Sugarcane Bagasse via Successive Homogeneous Transesterification Using Ionic Liquid.

Lignocellulosic agricultural waste is an abundant renewable feedstock that can be utilized as a sustainable source of biomass-based plastics. Ideally, it is used without discarding any components, including cellulose, hemicellulose, and lignin. However, their utilization as lignocellulose-based plastics has been limited because of the low compatibility between the polysaccharides and lignin derivatives and the resulting poor mechanical properties of the final products. Here, we demonstrate a facile but highly controllable conversion of sugarcane bagasse into valuable thermoplastics by utilizing the excellent solubility and unique organocatalytic abilities of an ionic liquid, 1-ethyl-3-methylimidazolium acetate. In a homogeneous and one-pot chemical modification reaction system, the substitution ratio of an aromatic benzoyl group to an aliphatic hexanoyl group in the bagasse derivative was adjusted by the ratio of acyl reagents used. Moreover, the allocation of these two acyl groups to polysaccharide and lignin components in bagasse was successfully controlled only by exchanging the order of the acyl reagents introduced into the reaction system. The controlled introduction of the acyl groups into bagasse achieved a homogeneous polymer phase in the resultant multicomponent hot-pressed film, resulting in enhanced mechanical properties such as sufficient tensile strength (∼20 MPa) and excellent ductility with a high strain energy density (∼5 MJ m-3).

Improved out-of-plane thermal conductivity of boron nitride nanosheet-filled polyamide 6/polyethylene terephthalate composites by a rapid solidification method

The randomly orientated m-BNNS could make the thermal conductivity of composite film as high as 3.28 W (m−1 K−1) at filler loading 55 wt%, which is 64% higher than that of directly hot-pressed film. The NEMD simulations also provide some explanations.

Microwave assisted heating of plastic waste: Effect of plastic/susceptor (SiC) contacting patterns

Plastic accumulation is a growing sustainability challenge. Most plastics are thermally inert at room temperature, requiring high temperatures for depolymerization. In the quest for developing sustainable plastic upcycling, we investigate silicon carbide (SiC) as microwave absorbing susceptors for reaching depolymerization temperatures. We utilize three SiC topologies – particles, hot-pressed plastic films containing SiC particles, and monoliths. SiC particles of >0.5 mm in diameter can provide heating rates approaching ∼200 °C/min at modest powers. Still, physically mixed plastic-susceptor beds suffer from density differences, causing non-uniform contact during plastic softening and melting. Hot-pressed plastic films containing SiC particles allow uniform plastic-susceptor contact but suffer from slow heating as only a single layer of susceptors exists between polymer layers. SiC monoliths mitigate these challenges by preferentially dissipating the microwaves and rapidly heating the plastics independently of polymeric properties.

Cellulose-based photo-enhanced persistent room-temperature phosphorescent materials by space stacking effects

Cellulose is environmentally friendly bio-based polymer with a large number of hydroxyl groups in its structure, which can easily form hydrogen bond networks. It has the potential to become excellent persistent room-temperature phosphorescence (pRTP) material through rational design. In this work, we reported a simple and universal strategy to obtain polymer film by connecting aromatic derivatives onto cellulose chains and drying them by hot press process. The emission color of pRTP from blue-green to red can be tuned by benzene or different polycyclic aromatic hydrocarbons as grafted groups, as well as the performance of photo-enhanced pRTP property. Notably, the lifetime of the best-performing film could be enhanced from 282.1 ms to 571.1 ms after irradiation for 1 min at room temperature. All the hot-pressed films were able to withstand Young's modulus up to nearly 18.0 GPa and tensile strength of around 80 MPa. The excellent luminescent and mechanical properties were derived from space stacking effects of the grafted groups and abundant intermolecular hydrogen bonding. These results will provide the effective design strategy for the modulation of smart-response pRTP materials, and expand the application range of cellulose-based materials.

Xylose-Based Polyethers and Polyesters Via ADMET Polymerization toward Polyethylene-Like Materials

One of the challenges of developing bioderived polymers is to obtain materials with competitive properties. This study investigates the structure-properties relationships of polyesters and polyethers that can be derived from d-xylose through metathesis polymerization, in order to produce bioderived plastic materials that are sourced from sustainable feedstocks and whose properties can compete with those of polyolefins such as polyethylene. Bicyclic diol 1,2-O-isopropylidene-α-d-xylofuranose was coupled with ω-unsaturated fatty acids and alcohols of different chain lengths (C11, C5, C3), and the resulting α,ω-unsaturated esters and ethers polymerized via an acyclic diene metathesis (ADMET) polymerization using a commercial Grubbs second-generation catalyst, obtaining polymers with Mn up to 63.0 kg mol–1. Glass transition temperatures (Tg) decreased linearly with increasing chain length and were lower for polyethers (−32 to 14 °C) compared to polyesters (−14 to 45 °C). ADMET polymers could be modified postpolymerization by reacting their internal carbon–carbon double bonds. Thiol–ene reaction with methyl thioglycolate lowered the Tg while allowing insertion of additional functional groups. Alkene hydrogenation turned the polyester and polyether with C20 hydrocarbon linkers into semicrystalline polymers with Tm ≈ 50 °C. The latter, when cast into films, displayed remarkable polyethylene-like properties. Hot-pressed films proved ductile materials (Young modulus Ey 60–110 MPa, elongation at break εb 670–1000%, ultimate tensile strength σb 8–10 MPa), while uniaxially oriented films proved very strong yet flexible materials (Ey 190–200 MPa, εb 160–350%, σb 43–66 MPa). Gas barrier properties were comparable to those of commercial polyolefins. Polyethers were resistant to hydrolysis, while polyesters depolymerized under alkaline conditions.

Microfibrillated cellulose film with enhanced mechanical and water-resistant properties by glycerol and hot-pressing treatment

In this study, the effects of glycerol and hot-pressing treatment were investigated to improve the water-resistance and mechanical properties of microfibrillated cellulose (MFC) films. Glycerol is commonly used to remedy the brittleness of MFC films; however, it substantially reduces the mechanical strength and water resistance of these films. A hot-pressing treatment is a simple and effective way to enhance these degraded properties. A combination of a glycerol additive and hot-pressing treatment was considered an economical and efficient approach to improve the performance of MFC films. The wet strength of a glycerol-plasticized, hot-pressed MFC film prepared using a glycerol solution with a concentration of 2.5% (v/v) (H-MFC/2.5%G) was almost thirteen times higher than that of an unmodified MFC film. In addition, the elongation and tensile strength of H-MFC/2.5%G were found to be 85% and 37% higher than those of the unmodified MFC film, respectively.

Eco-Friendly High-Strength Composites Based on Hot-Pressed Lignocellulose Microfibrils or Fibers

Unbleached lignocellulosic wood fiber materials of low porosity are of great interest as eco-friendly load-bearing materials because their yield is much higher than that for “pure” wood cellulosics. The difference between comparable materials based on lignocellulose fibers or nanocellulose is investigated. The structure, surface area, mechanical properties, moisture sorption, and optical properties of films based on fibers or microfibrillated lignocellulose (MFLC) were characterized as a function of lignin content, and the environmental impact was compared. The modulus and tensile strength of comparable fiber and MFLC films (≈25% porosity) increased up to an optimum lignin content (11–17%) and then decreased at a very high lignin content. Hot-pressed MFLC films with little porosity showed excellent properties, 230–260 MPa strength, 17–20 GPa modulus, and 81 MPa wet strength. The mechanical property values of hot-pressed wood fibers with 25% porosity were also as high as 154 MPa strength and 13.2 GPa modulus, which are higher than those of comparable materials reported in the literature. Because hot-pressed lignocellulose fibers can be readily recycled and show low cumulative energy demand, they are candidates for semistructural engineering materials. MFLC is of great interest for coatings, films, adhesives, and as additives or in high-technology applications.

Conversion of low-quality cotton to bioplastics

The use of eco-friendly bioplastics has become a viable solution to reduce the accumulation of petrochemical products in the biosphere and to decrease microplastic contamination. In this study, we used low-quality cotton fibers that lack textile applications to prepare bioplastics. We dissolved cotton fibers in N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) solvent system and converted cellulose solutions to strong, transparent, and flexible films through casting, gelation, regeneration, plasticization, and hot-pressing. Films were characterized using different analytical techniques to evaluate their physicochemical and mechanical properties. Compared to raw cotton cellulose, regenerated and hot-pressed cellulose films showed amorphous structures and excellent tensile characteristics. The physical and mechanical properties of cellulose films, such as deformation recovery, flexibility, homogeneity, elongation, and surface roughness, were significantly improved by means of plasticization and hot-pressing. Because glycerol plasticization increased the surface hydrophilicity of the films, plasma-induced surface grafting of oleic acid imparted hydrophobicity to cellulose films. This study presents a new avenue for using low-quality cotton fibers that are usually sold at a discounted price to produce value-added bioproducts for different applications.Graphic abstract

Enhanced contact properties of spray-coated AgNWs source and drain electrodes in oxide thin-film transistors

Facile patterning of electrodes is required for various electronic applications, particularly in solution-processed oxide thin-film transistors (TFTs). In this study, source and drain electrodes were prepared from silver nanowires (AgNWs) using spray-coating and hot press techniques. Although spray coating allowed production of AgNW patterns, which could function as electrodes in oxide TFT, the as-sprayed films did not provide a sufficient physical contact with oxide semiconductors and formed interspaces that impeded electron injection. At the same time, hot press technique produced denser AgNW networks that had a tight contact with the oxide semiconductors. As a result, hot-pressed films were considered as satisfactory source and drain electrodes for high-performance oxide TFTs, as they provided an easy electron injection. Finally, the prepared oxide TFTs with hot-pressed AgNW electrodes exhibited average field-effect mobility of 4.75 ± 1.5 cm2/V, significantly higher than that of the TFTs with as-sprayed AgNW electrodes (0.08 ± 0.05 cm2/V).

Comparison of crystallization behavior of Trans-1,4-polyisoprene under different crystallization temperature, pressure and tension

The crystallization of trans-1,4-polyisoprene (TPI) was influenced by many factors, such as the processing temperature, pressure and stress. The crystallization of TPI prepared under different conditions (temperature, pressure and tension) was characterized by Fourier transform infrared spectroscopy (FTIR), polarizing light microscopy(POM)and X-ray diffraction(XRD). The experimental results showed that the absorption frequency and the intensity of the FTIR spectra were not influenced by Mooney viscosity of TPI, however, it deeply affected by the sample preparation methods. The spectrum of hot pressed films showed a combination of α-form and β-form crystals, while that of solution cast films showed the characteristic absorption bands of α-form crystals and less β-form crystals. Spherulites of TPI could be obtained at several different crystallization temperatures (45 °C, 18 °C and 9 °C), but the size of the spherulites decreased from ~180 μm to ~70 μm with the decrease of temperature from 45 °C and 9 °C. When the temperature of the specimen decreased at a uniform rate (1.5 °C/min), large size spherulites were obtained. With the increase of pressure, the spherulites were not perfect. XRD patterns of TPI revealed that both α-form and β-form crystals existed in stretched specimens. Part of the α-form crystals transformed into β-form crystals during the extension.

Investigation on crystalline structure and dielectric relaxation behaviors of hot pressed poly(vinylidene fluoride) film

The dielectric relaxation behaviors of hot pressed poly(vinylidene fluoride) (PVDF) film have been studied using dielectric spectroscopy in the frequency domain from 20 Hz to 5 MHz at temperatures between 20 °C and 200 °C. Crystalline/amorphous interphase is suggested with methods of FTIR, XRD, and DSC. Frequency and temperature dependence of dielectric spectroscopy reveals the relaxation behavior and structural dynamics of the samples, and three types of relaxation processes are suggested, αAc relaxation process contributed by the hopping transport process near the periphery of conduction band or valence zones at Fermi energy, αc relaxation process related to the structure change of crystal lattice trapped dipoles in crystalline regions, and αa relaxation process arising from segmental dipole rearrangement of interphases in amorphous regions. Cole-Cole and Havriliak-Negami experimental equations were utilized to analyze these relaxation processes, and differences of Arrhenius parameters for αAc and αc relaxation processes obtained from Cole-Cole and Havriliak-Negami equations were discussed in detail. Activity energy of different relaxation processes obtained from Arrhenius equation and VFT equation indicates non-single thermal activation mechanism for hot pressed PVDF film.

Synthesis and thermal properties of paramylon mixed esters and optical, mechanical, and crystal properties of their hot-pressed films

Acylation of paramylon, a storage polysaccharide of Euglena gracilis, using multiple acid anhydrides yielded thermoplastic paramylon mixed esters without significant depolymerization. DSC examination showed that the shorter the acyl chain, the higher both the melting and glass transition temperature of the ester. TG analyses revealed their higher thermostability with the 5% weight loss temperature of ⿼330°C. Melt volume flow rate examination revealed that the longer the acyl chain, the higher the thermoplasticity of the ester and that the esters exhibited higher thermoplasticity than structurally analogous esters made from cellulose and curdlan. A notable feature of the thermoplastic paramylon mixed esters is the availability of hot-pressing as a means of molding them into a film. Light transmittance and XRD measurements revealed that these films were transparent and in the amorphous state. Tensile tests indicated that the films had adequate mechanical strength comparable to those of the cellulose and curdlan analogues.

Solvent vapor annealing induced polymorphic transformation of polybutene-1

Solvent annealing is a facile method for changing the aggregated microstructure and physical properties of polymer materials. In this paper, we addressed the effects of solvent vapor annealing, including chloroform and water vapor, on the polymorphic transformation in both hot-pressed film and electrospun nonwoven of isotactic polybutene-1 (PB-1) by means of in situ Fourier transform infrared spectroscopy (FTIR). The pretty rapid transition rate caused by the increased motion of molecular chains under chloroform vapor is associated with a lowest crystallinity. Also, a decreased crystallinity with the crystal transition occurred in electrospun nonwovens resulting from the relaxation of the stretched molecular chains into amorphous state rather than realignment into crystal form I predominating the crystal transition process.

Thermal extrusion of starch film with alcohol

A one-step thermal extrusion process has been investigated for the modification of starch with alcohol in order to improve the film properties. Unmodified starch/glycerol mixtures containing Methanol (MetOH), ethanol (EtOH) and their combinations (5, 10 and 15 wt%) were thermally extruded to produce thermoplastic. The final hot-pressed film showed increased stiffness and crystallinity, while having decreased moisture uptake due to oxidation and alcohol complexing molecular interactions. The Young's Modulus, tensile strength and elongation at break increased by 60%, 15% and 32% respectively, for 5 wt% MetOH derived film, compared to the control. The film moisture content was reduced by up to 15 wt% for 5 wt% EtOH-derived film. Generally the crystallinity increased in the alcohol-derived films due to an increased complexing of alcohol with starch forming the VH polymorph. Fourier transform infra-red (FTIR) and proton nuclear magnetic resonance (1HNMR) spectroscopic analysis were used to discuss the molecular interactions between the starch and alcohol molecules.