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CRUE-CSIC (Acuerdos Transformativos 2022), Current knowledge on the properties of different types of cellulose nanofibers (CNFs) is fragmented. Properties variation is very extensive, depending on raw materials, effectiveness of the treatments to extract the cellulose fraction from the lignocellulosic biomass, pretreatments to facilitate cellulose fibrillation and final mechanical process to separate the microfibrils. Literature offers multiple parameters to characterize the CNFs prepared by different routes. However, there is a lack of an extensive guide to compare the CNFs. In this study, we perform a critical comparison of rheological, compositional, and morphological features of CNFs, produced from the most representative types of woody plants, hardwood and softwood, using different types and intensities of pretreatments, including enzymatic, chemical and mechanical ones, and varying the severity of mechanical treatment focusing on the relationship between macroscopic and microscopic parameters. This structured information will be exceedingly useful to select the most appropriate CNF for a certain application based on the most relevant parameters in each case., Ministerio de Economía y Competitividad (España), Ministerio de Ciencia e Innovación (España), Comunidad de Madrid, Universidad Complutense de Madrid, Banco Santander, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

The dispersion degree of cellulose micro and nanofibrils (CMFs/CNFs) in water suspensions is key to understand and optimize their effectiveness in several applications. In this study, we proposed a method, based on gel point (Øg), to calculate both aspect ratio and dispersion degree. This methodology was validated through the morphological characterization of CMFs/CNFs by Transmission Electronic Microscopy. The influence of dispersion degree on the reinforcement of recycled cardboard has also been evaluated by stirring CMF/CNF suspensions at different speeds. Results show that as stirring speed increases, Øg decreased to a minimum value, in which the aspect ratio is maximum. Then, Øg increased again. Suspensions with lower Øg, in the intermediate region of agitation present very good dispersion behavior with an open and spongy network structure, in which nanofibril clusters are totally dispersed. Higher stirring speeds shorten the nanofibrils and the networks collapse. Results show that the dispersion of the nanocellulose at the minimum Øg before their addition to the pulp, produces higher mechanical properties, even higher than when CNFs and pulp are agitated together. This method allows for the determination of the CMF/CNF dispersion, to maximize their behavior as strength agents. This knowledge would be crucial to understand why some industrial trials did not give satisfactory results., Ministerio de Ciencia e Innovación (MICINN), Universidad Complutense de Madrid/Banco de Santander, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

The dispersion degree of cellulose micro and nanofibrils (CMFs/CNFs) in water suspensions is key to understand and optimize their effectiveness in several applications. In this study, we proposed a method, based on gel point (Øg), to calculate both aspect ratio and dispersion degree. This methodology was validated through the morphological characterization of CMFs/CNFs by Transmission Electronic Microscopy. The influence of dispersion degree on the reinforcement of recycled cardboard has also been evaluated by stirring CMF/CNF suspensions at different speeds. Results show that as stirring speed increases, Øg decreased to a minimum value, in which the aspect ratio is maximum. Then, Øg increased again. Suspensions with lower Øg, in the intermediate region of agitation present very good dispersion behavior with an open and spongy network structure, in which nanofibril clusters are totally dispersed. Higher stirring speeds shorten the nanofibrils and the networks collapse. Results show that the dispersion of the nanocellulose at the minimum Øg before their addition to the pulp, produces higher mechanical properties, even higher than when CNFs and pulp are agitated together. This method allows for the determination of the CMF/CNF dispersion, to maximize their behavior as strength agents. This knowledge would be crucial to understand why some industrial trials did not give satisfactory results., Ministerio de Ciencia e Innovación (MICINN), Universidad Complutense de Madrid/Banco de Santander, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

CRUE-CSIC (Acuerdos Transformativos 2022), Current knowledge on the properties of different types of cellulose nanofibers (CNFs) is fragmented. Properties variation is very extensive, depending on raw materials, effectiveness of the treatments to extract the cellulose fraction from the lignocellulosic biomass, pretreatments to facilitate cellulose fibrillation and final mechanical process to separate the microfibrils. Literature offers multiple parameters to characterize the CNFs prepared by different routes. However, there is a lack of an extensive guide to compare the CNFs. In this study, we perform a critical comparison of rheological, compositional, and morphological features of CNFs, produced from the most representative types of woody plants, hardwood and softwood, using different types and intensities of pretreatments, including enzymatic, chemical and mechanical ones, and varying the severity of mechanical treatment focusing on the relationship between macroscopic and microscopic parameters. This structured information will be exceedingly useful to select the most appropriate CNF for a certain application based on the most relevant parameters in each case., Ministerio de Economía y Competitividad (España), Ministerio de Ciencia e Innovación (España), Comunidad de Madrid, Universidad Complutense de Madrid, Banco Santander, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

Current knowledge on the properties of different types of cellulose nanofibers (CNFs) is fragmented. Properties variation is very extensive, depending on raw materials, effectiveness of the treatments to extract the cellulose fraction from the lignocellulosic biomass, pretreatments to facilitate cellulose fibrillation and final mechanical process to separate the microfibrils. Literature offers multiple parameters to characterize the CNFs prepared by different routes. However, there is a lack of an extensive guide to compare the CNFs. In this study, we perform a critical comparison of rheological, compositional, and morphological features of CNFs, produced from the most representative types of woody plants, hardwood and softwood, using different types and intensities of pretreatments, including enzymatic, chemical and mechanical ones, and varying the severity of mechanical treatment focusing on the relationship between macroscopic and microscopic parameters. This structured information will be exceedingly useful to select the most appropriate CNF for a certain application based on the most relevant parameters in each case.

The present paper proposes a novel approach for the morphological characterization of cellulose nano and microfibers suspensions (CMF/CNFs) based on the analysis of eroded CMF/CNF microscopy images. This approach offers a detailed morphological characterization and quantification of the micro and nanofibers networks present in the product, which allows the mode of fibrillation associated to the different CMF/CNF extraction conditions to be discerned. This information is needed to control CMF/CNF quality during industrial production. Five cellulose raw materials, from wood and non-wood sources, were subjected to mechanical, enzymatic, and (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO)-mediated oxidative pre-treatments followed by different homogenization sequences to obtain products of different morphologies. Skeleton analysis of microscopy images provided in-depth morphological information of CMF/CNFs that, complemented with aspect ratio information, estimated from gel point data, allowed the quantification of: (i) fibers peeling after mechanical pretreatment; (ii) fibers shortening induced by enzymes, and (iii) CMF/CNF entanglement from TEMPO-mediated oxidation. Being mostly based on optical microscopy and image analysis, the present method is easy to implement at industrial scale as a tool to monitor and control CMF/CNF quality and homogeneity., Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Universidad Complutense de Madrid/Banco de Santander, Ministerio de Ciencia e Innovación, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

Nanocellulose is an emerging material that needs to be well characterized to control its performance during industrial applications. Gel point (Øg) is a convenient parameter commonly used to estimate the aspect ratio (AR) of cellulose nano/microfibers (CNFs/CMFs), providing critical information on the nanofiber network. However, its estimation requires many sedimentation experiments, tedious and time consuming. In this study, a simpler and faster technique is presented to estimate Øg, based on one or two sedimentation experiments, reducing the experiments by a factor of at least 2.5. Here, this new methodology is successfully validated by using the Øg of different CNF/CMF hydrogels calculated with the traditional methodology, showing an error lower than 7%. The error in the estimation of the AR is lower than 3% in all cases. Furthermore, the two mathematical models currently used to estimate Øg, the smoothing spline and the quadratic fit, are compared and the mathematical assumptions improved., Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Universidad Complutense de Madrid/Banco de Santander, Australian Research Council, Australian Paper, Carter Holt Harvey, Circa, Norske Skog and Visy, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

Nanocellulose is an emerging material that needs to be well characterized to control its performance during industrial applications. Gel point (Øg) is a convenient parameter commonly used to estimate the aspect ratio (AR) of cellulose nano/microfibers (CNFs/CMFs), providing critical information on the nanofiber network. However, its estimation requires many sedimentation experiments, tedious and time consuming. In this study, a simpler and faster technique is presented to estimate Øg, based on one or two sedimentation experiments, reducing the experiments by a factor of at least 2.5. Here, this new methodology is successfully validated by using the Øg of different CNF/CMF hydrogels calculated with the traditional methodology, showing an error lower than 7%. The error in the estimation of the AR is lower than 3% in all cases. Furthermore, the two mathematical models currently used to estimate Øg, the smoothing spline and the quadratic fit, are compared and the mathematical assumptions improved., Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Universidad Complutense de Madrid/Banco de Santander, Australian Research Council, Australian Paper, Carter Holt Harvey, Circa, Norske Skog and Visy, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

The present paper proposes a novel approach for the morphological characterization of cellulose nano and microfibers suspensions (CMF/CNFs) based on the analysis of eroded CMF/CNF microscopy images. This approach offers a detailed morphological characterization and quantification of the micro and nanofibers networks present in the product, which allows the mode of fibrillation associated to the different CMF/CNF extraction conditions to be discerned. This information is needed to control CMF/CNF quality during industrial production. Five cellulose raw materials, from wood and non-wood sources, were subjected to mechanical, enzymatic, and (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO)-mediated oxidative pre-treatments followed by different homogenization sequences to obtain products of different morphologies. Skeleton analysis of microscopy images provided in-depth morphological information of CMF/CNFs that, complemented with aspect ratio information, estimated from gel point data, allowed the quantification of: (i) fibers peeling after mechanical pretreatment; (ii) fibers shortening induced by enzymes, and (iii) CMF/CNF entanglement from TEMPO-mediated oxidation. Being mostly based on optical microscopy and image analysis, the present method is easy to implement at industrial scale as a tool to monitor and control CMF/CNF quality and homogeneity., Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Universidad Complutense de Madrid/Banco de Santander, Ministerio de Ciencia e Innovación, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

This study examines and quantifies the effect of adding polyelectrolytes to cellulose nanofibre suspensions on the gel point of cellulose nanofibre suspensions, which is the lowest solids concentration at which the suspension forms a continuous network. The lower the gel point, the faster the drainage time to produce a sheet and the higher the porosity of the final sheet formed. Two new techniques were designed to measure the dynamic compressibility and the drainability of nanocellulose–polyelectrolyte suspensions. We developed a master curve which showed that the independent variable controlling the behaviour of nanocellulose suspensions and its composite is the structure of the flocculated suspension which is best quantified as the gel point. This was independent of the type of polyelectrolyte used. At an addition level of 2 mg/g of nanofibre, a reduction in gel point over 50 % was achieved using either a high molecular weight (13 MDa) linear cationic polyacrylamide (CPAM, 40 % charge), a dendrimer polyethylenimine of high molecular weight of 750,000 Da (HPEI) or even a low molecular weight of 2000 Da (LPEI). There was no significant difference in the minimum gel point achieved, despite the difference in polyelectrolyte morphology and molecular weight. In this paper, we show that the gel point controls the flow through the fibre suspension, even when comparing fibre suspensions with solids content above the gel point. A lower gel point makes it easier for water to drain through the fibre network,reducing the pressure required to achieve a given dewatering rate and reducing the filtering time required to form a wet laid sheet. We further show that the lower gel point partially controls the structure of the wet laid sheet after it is dried. Halving the gel point increased the air permeability of the dry sheet by 37, 46 and 25 %, when using CPAM, HPEI and LPEI, respectively. The resistance to liquid flow was reduced by 74 and 90 %, when using CPAM and LPEI. Analysing

The phase transitions, structure, and rheological properties of the carboxymethyl cellulose-water system were studied via the turbidity-point method, viscometry, polarization microscopy, and the turbidityspectrum method as well as with a polarization photoelectric unit. The regions of existence of the isotropic and anisotropic phases, the gel point, and the concentration dependence of the supramolecular-particle size were determined. Magnetic-field application results in a gain in the viscosities of carboxymethyl cellulose solutions. © 2013 Pleiades Publishing, Ltd.

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In this work the crosslinking behaviour of two silane-grafted polyethylenes was investigated with respect to time and temperature by using dynamic rheological measurements. It has been found that inhomogeneous character of the crosslinking reaction takes place in both tested samples. By utilization of G′-G" crossover method, it has been found that the sample with initially distinct crosslinking state and short critical crosslinking reaction time has high tendency to create small gels during production of hot water pipes. It has also been revealed that the temperature dependence of the critical time, at which the crosslinking speed is the highest, shows an Arrhenius-type behaviour. © 2013 AIP Publishing LLC.

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In this work the crosslinking behaviour of two silane-grafted polyethylenes was investigated with respect to time and temperature by using dynamic rheological measurements. It has been found that inhomogeneous character of the crosslinking reaction takes place in both tested samples. By utilization of G′-G" crossover method, it has been found that the sample with initially distinct crosslinking state and short critical crosslinking reaction time has high tendency to create small gels during production of hot water pipes. It has also been revealed that the temperature dependence of the critical time, at which the crosslinking speed is the highest, shows an Arrhenius-type behaviour. © 2013 AIP Publishing LLC.

[EN] In the last years, some high renewable content epoxy resins, derived from vegetable oils, have been developed at industrial level and are now commercially available; these can compete with petroleum-based resins as thermoset matrices for composite materials. Nevertheless, due to the relatively high cost in comparison to petroleum-based resins, their use is still restricted to applications with relatively low volume consumption such as model making, tuning components, nautical parts, special effects, outdoor sculptures, etc. in which, the use of composite laminates with carbon, aramid and, mainly, glass fibers is generalized by using hand layup and vacuum assisted resin transfer molding (VARTM) techniques due to low manufacturing costs and easy implementation. In this work, we study the behavior of two high renewable content epoxy resins derived from vegetable oils as potential substitutes of petroleum-based epoxies in composite laminates with flax reinforcements by using the VARTM technique. The curing behavior of the different epoxy resins is compared in terms of the gel point and exothermicity profile by differential scanning calorimetry (DSC). In addition, overall performance of flax-epoxy composites is compared with standardized mechanical (tensile, flexural and impact) and thermal (Vicat softening temperature, heat deflection temperature, thermo-mechanical analysis) tests. The curing DSC profiles of the two eco-friendly epoxy resins are similar to a conventional epoxy resin. They can be easily handled and processed by conventional VARTM process thus leading to composite laminates with flax with balanced mechanical and thermal properties, similar or even higher to a multipurpose epoxy resin. © 2012 Society of Plastics Engineers.

[EN] In the last years, some high renewable content epoxy resins, derived from vegetable oils, have been developed at industrial level and are now commercially available; these can compete with petroleum-based resins as thermoset matrices for composite materials. Nevertheless, due to the relatively high cost in comparison to petroleum-based resins, their use is still restricted to applications with relatively low volume consumption such as model making, tuning components, nautical parts, special effects, outdoor sculptures, etc. in which, the use of composite laminates with carbon, aramid and, mainly, glass fibers is generalized by using hand layup and vacuum assisted resin transfer molding (VARTM) techniques due to low manufacturing costs and easy implementation. In this work, we study the behavior of two high renewable content epoxy resins derived from vegetable oils as potential substitutes of petroleum-based epoxies in composite laminates with flax reinforcements by using the VARTM technique. The curing behavior of the different epoxy resins is compared in terms of the gel point and exothermicity profile by differential scanning calorimetry (DSC). In addition, overall performance of flax-epoxy composites is compared with standardized mechanical (tensile, flexural and impact) and thermal (Vicat softening temperature, heat deflection temperature, thermo-mechanical analysis) tests. The curing DSC profiles of the two eco-friendly epoxy resins are similar to a conventional epoxy resin. They can be easily handled and processed by conventional VARTM process thus leading to composite laminates with flax with balanced mechanical and thermal properties, similar or even higher to a multipurpose epoxy resin. © 2012 Society of Plastics Engineers.

Tato diplomová práce se zabývá studiem závislosti doby zgelovatění na teplotě po přídavku vybraných draselných solí a následnou instrumentální analýzou vzniklých produktů. Těmito draselnými solemi jsou KCl, KBr, KI, K2SO4 a KNO3. Použité instrumentální metody byly XRD, FTIR a SEM. Na základě měření bylo zjištěno, že přídavek draselných solí nemá statisticky významný vliv na dobu zgelovatění. Ze směrnic zlinearizovaných grafů závislosti doby zgelovatění na teplotě se jeví, že přídavek solí má mírný vliv na aktivační energii studované reakce. Z XRD, FTIR a SEM analýzy vyplynulo, že krystalická struktura, která vznikla polykondenzační reakcí, je phillipsit. Tato struktura nebyla prokázána u gelu s přídavkem K2SO4., This thesis studied the gel point time depending on the temperature after addition of selected potassium salts and subsequent instrumental analysis of the resulting products. These potassium salts were KCl, KBr, KI, KNO3 and K2SO4. Used instrumental methods were XRD, FTIR and SEM. Based on these measurements it was found, that the addition of potassium salt had no effect on gel point time. The guidelines of linearized graphs forms showed that the addition of salt had an affects to the activation energy. The XRD, FTIR and SEM analysis showed that the crystalline structure, which was prepared in polycon-densation reaction, was phillipsit. This structure was not been demonstrated in a gel with the addition of K2SO4., Ústav inženýrství ochrany životního prostředí, obhájeno

We study the kinetics of transient network formation by monodisperse telechelic polypeptides with collagen-like end blocks and a random coil middle block. Upon cooling, the end blocks associate reversibly into triple helices, leading to gels with well-defined, trimeric crosslinks. Formation of triple helices occurs in two steps: nucleation and propagation. At low protein concentrations, when a simultaneous encounter of three end blocks is rather infrequent, the limiting step is nucleation. With increasing concentration, propagation of triple helix becomes rate-limiting. The rate of helix formation controls the gelation process and the development of mechanical (rheological) properties. Not all helices contribute junctions to the developing network: a certain fraction forms mechanically irrelevant loops, particularly at low concentrations. We show, however, that it is possible to predict the time dependent gel properties with the help of an analytical model which accounts for loops and dangling ends. A connection between helix content and storage modulus can be established. Using this model we can accurately account for the experimental data.

Using a rheometer coupled with an UV-light generator, the viscoelastic behaviour during the fast cure of star-branched polyester is investigated. The 32 arm star polymers consist of a hyperbranched polyester core, Boltorn(TM) and linear grafts of poly(E-caprolactone) (degree of polymerisation: 20-52) with methacrylate end groups. The resins are crystalline and the melting points range from 34 to 50degreesC; films can be formed and cured below 80degreesC. The crossover of G' and G was used as the gel point. The time to reach the gel point, a few seconds, increases linearly with molecular weight., QC 20100525 NR 20140804

The use of powder coatings has increased steadily over thelast few decades. Their popularity is due to a number of majoradvantages they offer when compared to solvent-borne systems.Near zero VOC-content, reduced energy consumption and near 100%utilisation of the material are some of the advantages. Themain components in most thermoset powder coatings are a primaryresin and a binder. The coating is applied in powder form, thenbaked and cured i.e. cross-linked. Traditionally, thecross-link reaction has been controlled by temperature. Normalcuring temperatures range between 160 and 200 °C, and thusare not suitable for applications involving heat sensitivesubstrates such as wood and plastic. One way to lower thecuring temperature is by the introduction of semi-crystallinematerial with a suitable melting temperature. The advantage ofusing a crystalline resin is its rapid melting, a first ordertransition, versus the slow softening of an amorphous resin.Low curing temperature also requires an initiating system thatis activated at low temperatures while stable at roomtemperature. This is difficult to achieve with conventionalthermal initiators. In recent yearsUV-curing of powdercoatings has obtained increased attention in industrialresearch. This technique allows fast curing at lowertemperatures than conventional powder coatings. The researchinto UV-curing was triggered by the interest in using heatsensitive substrates. Other advantages are improved storagestability, elimination of premature reaction duringmanufacturing and better levelling since viscosity does notincrease until UV-irradiated. This thesis describes thesynthesis and characterisation of a series of branchedpolyesters and investigates their possible use as powdercoatings resins. The polyesters consist of poly(e-caprolactone)(PCL) (degree of polymerisation: 5-200) initiated fromhydroxyfunctional cores with methylmethacrylate end-capping .The cores utilised are: (1) 3rd-generation Boltorn, acommercially availabl, NR 20140805