Polyfluoroalkyl-silica porous coatings with high antireflection properties and low surface free energy for glass in solar energy application

Polyfluoroalkyl-silica porous coating stacks with durable antireflection (AR) properties have been obtained for photovoltaic (PV) application. An acid-catalyzed sol-gel process combined with evaporation induced self-assembly and the presence of a non-hydrolyzable polyfluoroalkyl group linked to the central atom of the silicon alkoxide was conducted. The aim was to obtain a low surface energy coating, devised to mitigate soiling adherence, without losing the AR properties of a baseline coating. In particular, the influence of polyfluoroalkyl chain length on the thickness, the water contact angle and optical transmission properties was first analyzed. The optimized polyfluoroalkyl-silica porous coating presented low surface energy < 20 mJ/m2, even with the desired low roughness values required for obtaining a negligible scattering of the incoming solar radiation. This coating was studied as an AR mono-layer and as an external coating in an AR bi-layer stack, with the presence of an inner dense-structured silica layer, that contributed to both the optical performance and durability, acting as an alkali diffusion preventing layer. The AR bi-layer stack deposited on two sides of glass provided a transmittance gain of 7.1%. Those optical properties were inalterable after accelerated aging tests, which sustains the reliability of the materials for solar energy applications.This work was supported by the Basque Government through EMAITEK 2017 program as well as the ELKARTEK projects FRONTIERS-2 (contract number KK2016-00093 ) and FRONTIERS-3 (contract number KK2017-00096 ). The authors thank ICV-CSIC, Yolanda Castro and Alicia Durán for their support with ellipsometry and EEP measurements. The authors thank Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) for their collaboration with the aging tests. The authors thank Miguel Pérez-Aradros for the help with graphical abstract illustration

Antireflective mesoporous silica coatings by optimization of water content in acid-catalyzed sol-gel method for application in glass covers of concentrated photovoltaic modules

Porous silica layers with outstanding antireflective properties have been prepared by acid-catalyzed sol-gel process in presence of organic phases as structure directing agents (SDA) and excess water, with the aim of offering a cost-competitive, easy up-scaling and high efficiency process that contributes to reduce current levelized cost of energy (LCOE) of concentrating photovoltaics (CPV). The process has been optimized by controlling the water/alkoxide ratio, which is an important structure-regulating tool, having a strong influence in the structural properties of sol-gel synthesized materials. Hydrolysis of the inorganic precursor has been accomplished in high water/alkoxide conditions and in the presence of SDAs. Evaporation induced self-assembly (EISA) during coating deposition and the scanning of four types of SDAs have permitted to select the coating that fulfilled specific thickness and refractive index values with, in parallel, excellent results on sol stability. The final optimization has produced mesoporous coatings with ∼9 nm mean pore size, leading to an enhancement in transmittance up to 7.4% over bare glass in the 300–1500 nm wavelength range. The transmittance spectra have been used as inputs for the theoretical calculation of the short-circuit current density of a commercially available multijunction solar cell for CPV applications.This work was supported by the Basque Government for EMAI-TEK 2017 program as well as theELKARTEK projects FRONTIERS-2(contract number KK2016-00093) and FRONTIERS-3 (contractnumber KK2017-00096). The authors thank ICV-CSIC, Yolanda Cas-tro and Alicia Durán for ellipsometry and EEP measurements. Theauthors thank Miguel Pérez-Aradros for the help with graphicalabstract illustration

Bio-Based Polyurethane Networks Derived from Liquefied Sawdust

The utilization of forestry waste resources in the production of polyurethane resins is a promising green alternative to the use of unsustainable resources. Liquefaction of wood-based biomass gives polyols with properties depending on the reagents used. In this article, the liquefaction of forestry wastes, including sawdust, in solvents such as glycerol and polyethylene glycol was investigated. The liquefaction process was carried out at temperatures of 120, 150, and 170 °C. The resulting bio-polyols were analyzed for process efficiency, hydroxyl number, water content, viscosity, and structural features using the Fourier transform infrared spectroscopy (FTIR). The optimum liquefaction temperature was 150 °C and the time of 6 h. Comprehensive analysis of polyol properties shows high biomass conversion and hydroxyl number in the range of 238–815 mg KOH/g. This may indicate that bio-polyols may be used as a potential substitute for petrochemical polyols. During polyurethane synthesis, materials with more than 80 wt% of bio-polyol were obtained. The materials were obtained by a one-step method by hot-pressing for 15 min at 100 °C and a pressure of 5 MPa with an NCO:OH ratio of 1:1 and 1.2:1. Dynamical-mechanical analysis (DMA) showed a high modulus of elasticity in the range of 62–839 MPa which depends on the reaction conditions.The authors would like to thank the National Science Centre of Poland (No. 2018/02/X/ST5/02784) for financial support

Highly hydrophobic cellulose acetate mats modified with poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymer and TiO2 nanoparticles by electrospinning

Cellulose acetate (CA) mats modified with poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (PEO-b-PPO-b-PEO or EPE) and sol–gel synthesised titanium oxide (TiO2) nanoparticles were successfully fabricated by using electrospinning technique. Under the same preparation conditions, higher spinnability was achieved for EPE triblock copolymers modified mats. All fabricated mats showed a micrometric multilayer structure, which enabled layer-by-layer peeling. The addition of TiO2 nanoparticles facilitated the peeling process. The diameter of the fibres was ~ 3 times lower after the incorporation of sol–gel synthesised TiO2 nanoparticles. TEM images confirmed that under electrospinning conditions the PPO block domains were able to microphase separated from the PEO block/CA phase. Additionally, the introduction of sol–gel synthesised TiO2 nanoparticles led to an inorganic network formation with nanoparticle size equal to ~ 8 nm in diameter. Moreover, the addition of TiO2 nanoparticles increased the hydrophobicity of the mats and their self-cleaning ability, being more effective for TiO2/CA than for TiO2-EPE/CA due to the partial absorption of water by EPE triblock copolymer. Young’s modulus of fabricated mats improved drastically with the addition of TiO2 nanoparticles, as well as their physical integrity in polar and nonpolar solvents. Fabricated mats with enhanced spinnability, which maintain CA mat features as well as the properties associated with sol–gel synthesised TiO2 nanoparticles, can find a wide range of applications.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This work was founded by Spanish Ministry of Science, Innovation and Universities and European Union (MICINN/FEDER and UE) in the frame of PGC2018-097699-B-I00 and PID2021-126417NB-I00 projects, and by Basque Government in frame of PIBA19-0044. J.G.-H.-de-M. thanks Basque Government for PhD Fellowship (PRE_2021_2_0044)

Predicted Studies of Branched and Cross-Linked Polyurethanes Based on Polyhydroxybutyrate with Polycaprolactone Triol in Soft Segments

The number of cross-links in the non-linear polyurethane structure is the basic factor affecting its properties. Selected properties of aliphatic polyurethanes with soft segments made of different amounts of polycaprolactonetriol, polycaprolactonediol and synthetic, telechelic poly([R,S]-3-hydroxybutyrate) were determined. On the basis of changes in polyurethane properties, the correlation between these properties and the construction of soft segments was found. The structure of polyurethanes, their morphology, hydrophilicity, thermal and mechanical properties were examined. These properties were changed linearly up to 15% content of polycaprolactonetriol in soft segments. A further increase in the amount of triol causes that these properties are mainly determined by the high number of cross-links.This research was founded by the National Science Center Miniatura 2 project no. 2018/02/X/ST5/02005 and partially by the UMG research project no. WPiT/2020/PZ/01

Degradability of Polyurethanes and Their Blends with Polylactide, Chitosan and Starch

One of the methods of making traditional polymers more environmentally friendly is to modify them with natural materials or their biodegradable, synthetic equivalents. It was assumed that blends with polylactide (PLA), polysaccharides: chitosan (Ch) and starch (St) of branched polyurethane (PUR) based on synthetic poly([R,S]-3-hydroxybutyrate) (R,S-PHB) would degrade faster in the processes of hydrolysis and oxidation than pure PUR. For the sake of simplicity in the publication, all three modifiers: commercial PLA, Ch created by chemical modification of chitin and St are called bioadditives. The samples were incubated in a hydrolytic and oxidizing environment for 36 weeks and 11 weeks, respectively. The degradation process was assessed by observation of the chemical structure as well as the change in the mass of the samples, their molecular weight, surface morphology and thermal properties. It was found that the PUR samples with the highest amount of R,S-PHB and the lowest amount of polycaprolactone triol (PCLtriol) were degraded the most. Moreover, blending with St had the greatest impact on the susceptibility to degradation of PUR. However, the rate of weight loss of the samples was low, and after 36 weeks of incubation in the hydrolytic solution, it did not exceed 7% by weight. The weight loss of Ch and PLA blends was even smaller. However, a significant reduction in molecular weight, changes in morphology and changes in thermal properties indicated that the degradation of the samples should occur quickly after this time. Therefore, when using these polyurethanes and their blends, it should be taken into account that they should decompose slowly in their initial life. In summary, this process can be modified by changing the amount of R,S-PHB, the degree of cross-linking, and the type and amount of second blend component added (bioadditives).This research was founded by the National Science Center Poland Miniatura 2 project no. 2018/02/X/ST5/02005 and partially by the UMG research project no. WZNJ/2021/PZ/02

Compatibility of Sustainable Mater-Bi/poly(ε-caprolactone)/cellulose Biocomposites as a Function of Filler Modification

Despite their popularity and multiplicity of applications, wood–polymer composites (WPCs) still have to overcome particular issues related to their processing and properties. The main aspect is the compatibility with plant-based materials which affects the overall performance of the material. It can be enhanced by strengthening the interfacial adhesion resulting from physical and/or chemical interactions between the matrix and filler, which requires introducing a compatibilizer or a proper modification of one or both phases. Herein, the impact of cellulose filler modifications with varying contents (1–10 wt%) of hexamethylene diisocyanate (HDI) on the compatibility of Mater-Bi/poly(ε-caprolactone) (PCL)-based biocomposites was evaluated. An analysis of surface wettability revealed that the filler modification reduced the hydrophilicity gap between phases, suggesting compatibility enhancement. It was later confirmed via microscopic observation (scanning electron microscopy (SEM) and atomic force microscopy (AFM)), which pointed to the finer dispersion of modified particles and enhanced quality of the interface. The rheological analysis confirmed increased system homogeneity by the reduction in complex viscosity. In contrast, thermogravimetric analysis (TGA) indicated the efficient modification of filler and the presence of the chemical interactions at the interface by the shift of thermal decomposition onset and the changes in the degradation course.This work was supported by the National Science Centre (NCN, Poland) in the frame of SONATINA 2 project 2018/28/C/ST8/00187—Structure and properties of lignocellulosic fillers modified in situ during reactive extrusion. The study was partially co-funded under project with grants for education allocated by the Ministry of Science and Higher Education in Poland executed under the subject of No 0613/SBAD/4820

Isothermal Crystallization Kinetics and Morphology of Double Crystalline PCL/PBS Blends Mixed with a Polycarbonate/MWCNTs Masterbatch

In this work, the 70/30 and 30/70 w/w polycaprolactone (PCL)/polybutylene succinate (PBS) blends and their corresponding PCL/PBS/(polycarbonate (PC)/multiwalled carbon nanotubes (MWCNTs) masterbatch) nanocomposites were prepared in a twin-screw extruder. The nanocomposites contained 1.0 and 4.0 wt% MWCNTs. The blends showed a sea-island morphology typical of immiscible blends. For the nanocomposites, three phases were formed: (i) The matrix (either PCL- or PBS-rich phase depending on the composition), (ii) dispersed polymer droplets of small size (either PCL- or PBS-rich phase depending on the composition), and (iii) dispersed aggregates of tens of micron sizes identified as PC/MWCNTs masterbatch. Atomic force microscopy (AFM) results showed that although most MWCNTs were located in the PC dispersed phase, some of them migrated to the polymer matrix. This is due to the partial miscibility and intimate contact at the interfaces between blend components. Non-isothermal differential scanning calorimetry (DSC) scans for the PCL/PBS blends showed an increase in the crystallization temperature (Tc) of the PCL-rich phase indicating a nucleation effect caused by the PBS-rich phase. For the nanocomposites, there was a decrease in Tc values. This was attributed to a competition between two effects: (1) The partial miscibility of the PC-rich and the PCL-rich and PBS-rich phases, and (2) the nucleation effect of the MWCNTs. The decrease in Tc values indicated that miscibility was the dominating effect. Isothermal crystallization results showed that the nanocomposites crystallized slower than the neat blends and the homopolymers. The introduction of the masterbatch generally increased the thermal conductivity of the blend nanocomposites and affected the mechanical properties.Thandi P. Gumede was financially supported by the National Research Foundation and the Sasol Inzalo Foundation in South Africa, while the POLYMAT/UPV/EHU team was funded by the following projects: “UPV/EHU Infrastructure: INF 14/38”; “Mineco/FEDER: SINF 130I001726XV1/Ref: UNPV13–4E–1726” and MINECO MAT2017-83014-C2-1-P. The publication of this article was funded by the Qatar National Library

Degradability of cross-linked polyurethanes/chitosan composites

Polyurethanes with synthetic poly([R,S]-3-hydroxybutyrate) in the soft segment and with polycaprolactone triol as cross-linker were blended with chitosan and degraded in hydrolytic and oxidative solutions. Progress of the degradation of the samples was evaluated by changes in their weight, surface topography and thermal properties. Increasing the poly([R,S]-3-hydroxybutyrate) content in soft segment as well as blending with chitosan resulted in an increase in degradability of cross-linked polyurethanes in both solutions.Centre of Polymer and Carbon Materials, Polish Academy of Sciences, University of Wolverhampton, University of the Basque Country (UPV/EHU), Gdynia Maritime Universit

Morphology, Thermo-Mechanical Properties and Biodegradibility of PCL/PLA Blends Reactively Compatibilized by Different Organic Peroxides

Reactive blending is a promising approach for the sustainable development of bio-based polymer blends and composites, which currently is gaining more and more attention. In this paper, biodegradable blends based on poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) were prepared via reactive blending performed in an internal mixer. The PCL and PLA content varied in a ratio of 70/30 and 55/45. Reactive modification of PCL/PLA via liquid organic peroxides (OP) including 0.5 wt.% of tert-butyl cumyl peroxide (BU), 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane (HX), and tert-butyl peroxybenzoate (PB) is reported. The materials were characterized by rotational rheometer, atomic force microscopy (AFM), thermogravimetry (TGA), differential scanning calorimetry (DSC), tensile tests and biodegradability tests. It was found that the application of peroxides improves the miscibility between PCL and PLA resulted in enhanced mechanical properties and more uniform morphology. Moreover, it was observed that the biodegradation rate of PCL/PLA blends reactively compatibilized was lower comparing to unmodified samples and strongly dependent on the blend ratio and peroxide structure. The presented results confirmed that reactive blending supported by organic peroxide is a promising approach for tailoring novel biodegradable polymeric systems with controllable biodegradation rates.This research work was funded by the National Science Centre (NCN Poland) grant number PRELUDIUM 15 project 2018/29/N/ST8/02042