Experimental and Modelling Studies of Water Sorption Properties of Cellulosic Derivative Fibers.

The objective of this study was to understand the chemical modification impact on interactions between water and cellulosic fiber. In that respect, cotton (C), flax (F), viscose (V) and cellulose acetate (CA) were analyzed by using a dynamic vapor sorption analysis. The sorption and desorption isotherms and kinetic curves were modelled using the Park model and the “Parallel Exponential Kinetics” (PEK) model-which allowed an accurate fitting on the whole range of water activity. The obtained sorption properties were correlated to the accessibility and the amount of sorption sites and also to the crystallinity level of the fibers. It was found that V exhibited the highest water sorption capacity due to a higher hydroxyl groups accessibility and a high amorphous fraction, followed up by F, C and CA. In contrast, higher kinetic sorption rate was obtained for CA due to a decrease of the hydroxyl groups within the fibers. Regardless the fiber, the determination of characteristic times showed that the kinetic rate was higher for sorption than desorption.

Improvement of Barrier Properties of Biodegradable Polybutylene Succinate/Graphene Nanoplatelets Nanocomposites Prepared by Melt Process

Polybutylene Succinate (PBS)/Graphene nanoplatelets (GnP) nanocomposites over a range of GnP from 0 to 1.35 wt.%. were prepared by a melt process. A mixture of individual graphene nanosheets and aggregates was obtained by the addition of GnP in the PBS matrix. The presence of these fillers did not significantly modify the morphology, crystalline microstructure of the matrix or its thermal stability. However, a slight reinforcement effect of PBS was reported in the presence of GnP. The water sorption isotherm modelling with Guggenheim, Andersen and De Boer (GAB) equation and Zimm-Lundberg theory allowed a phenomenological analysis at the molecular scale. The presence of GnP did not modify the water sorption capacity of the PBS matrix. From a kinetic point of view, a decrease of the diffusion coefficient with the increasing GnP content was obtained and was attributed to a tortuosity effect. The influence of water activity was discussed over a range of 0.5 to 1 and 0 to 0.9 for water and dioxygen permeability. Improvement of the barrier properties by 38% and 35% for water and dioxygen permeability respectively were obtained.

Metal- and Halide-Free, Solid-State Polymeric Water Vapor Sorbents for Efficient Water-Sorption-Driven Cooling and Atmospheric Water Harvesting

Metal- and halide-free, solid-state water vapor sorbents are highly desirable for water-sorption-based applications, because most of the solid sorbents are suffering from low water sorption capacity or toxic metals, while...

THERMAL, MECHANICAL AND WATER SORPTION PROPERTIES OF XANTHAN-BASED COMPOSITE CRYOGELS

The thermal, mechanical, rheological, and surface characteristics of some xanthan/poly(vinyl alcohol)/red grape pomace composite cryogels prepared by the freeze/thawing approach were investigated. The results were discussed in comparison with those obtained for individual xanthan or poly(vinyl alcohol) cryogel networks synthesized under the same conditions. The mechanical strength of the cryogels was enhanced by increasing the number of freeze/thawing cycles, and by the addition of a natural polyphenol (i.e. red grape pomace). The thermal stability of the poly(vinyl alcohol) in the blend significantly decreased upon the addition of 50% xanthan, while the presence of a single neat melting profile indicated good component miscibility for the chosen ratios. The water sorption capacity depended on the amount of polyphenol incorporated, thus the hydrophilicity of the cryogel films decreased with the increase of polyphenol content.

The influence of the ammonia concentration and the water content on the water sorption behavior of ambient pressure dried silica xerogels

Porous silica xerogels were synthesized within 10 h by a two-step sol–gel process under atmospheric conditions. In the first step, tetraethylorthosiloxane (TEOS) was hydrolyzed with water using sulfuric acid as a catalyst. In the second step, water and ammonia were added to the prehydrolyzed silica sol prior to the drying of the samples at 150 °C. The influence of the ammonia concentration and the water content on the physicochemical properties and the water sorption behavior of silica xerogels produced in the aforementioned way was investigated. The resulting silica xerogels were characterized by helium pycnometry, scanning electron microscopy, fourier-transform infrared spectroscopy, nitrogen sorption, and water sorption. It was shown that a higher ammonia concentration leads to an increased pore size of the silica xerogel which starts to adsorb water at a higher relative pressure. With an increased water content during gelation, the silica xerogel has a higher specific surface area and a higher water sorption capacity. Furthermore, silica xerogels can be tailored by a controlled addition of ammonia and water to have a higher water sorption capacity than the reference silica gel over the whole range of relative pressure.

Study on the Moisture Absorption and Thermal Properties of Hygroscopic Exothermic Fibers and Related Interactions with Water Molecules

The aim of this paper is to study the hygroscopic behavior of hygroscopic exothermic fiber-based materials and to obtain a better understanding of the thermal performance of these fibers during the moisture absorption process. The temperature distribution of different kinds of hygroscopic exothermic fibers in the process of moisture absorption, observed by infrared camera, demonstrated two types of heating performance of these fibers, which might be related to its hygroscopic behavior. Based on the sorption isotherms, a Guggenheim-Anderson-de Boer (GAB) multi-layer adsorption model was selected as the optimal moisture absorption fitting model to describe the moisture absorption process of these fibers, which illustrated that water sorption capacity and the water–fiber/water–water interaction had a significant influence on its heating performance. The net isosteric heats of sorption decreased with an increase of moisture content, which further explained the main factor affecting the heat dissipation of fibers under different moisture contents. The state of adsorbed water and water vapor interaction on the fiber surface were studied by simultaneous thermal analysis (TGA-DSC) measurement. The percentage of bound and unbound water formation at low and high humidity had a profound effect on the thermal performance of fibers. It can therefore be concluded that the content of tightly bound water a strong water–fiber interaction was the main factor affecting the heating performance of fibers at low moisture content, and the content of loosely bound water reflected that water sorption capacity was the main factor affecting the heating performance of fibers at high moisture content. This was further proven by the heat of desorption.

Assessment of Performance of Posidona oceanica (L.) as Biosorbent for Crude Oil-Spill Cleanup in Seawater

The marine environment is constantly at risk of pollution by hydrocarbon spills that requires its cleanup to protect the environment and human health. Posidonia oceanica (L.) (PO) beach balls, which are characteristic of the Mediterranean Sea and abundant on the beaches, are used as biosorbent to remove hydrocarbons from the sea. The impact of several factors such as oil concentration, time sorption, and weight sorbent was investigated to determine the oil and water sorption capacity for raw and milled P. oceanica fibers. The study of kinetic models for initial crude oil concentration of 2.5, 5, 8.8, 10, 15, 20, 30, and 40 g/L revealed that crude uptake followed the pseudo-first-order model while, for isotherm models, the crude uptake onto the P. oceanica tended to fit the Langmuir model. Experiments were performed according to two systems: a pure oil and pure water system and a mixed oil/water system. For the dry system (pure oil and pure water), the maximum oil and water sorption capacity of raw and milled fibers was found to be 5.5 g/g and 14 g/g for oil and 14.95 g/g and 15.84 g/g for water, respectively, whereas, in the mixed oil/water system, the maximum oil and water sorption capacity was estimated as 4.74 g/g, 12.80 g/g and 7.41 g/g, 8.31 g/g, respectively. The results showed that, in spite of their absorbency of a lot of water, the milled fibers with grain size ranging between 0.5 mm and 1 mm might be the relevant sorbent for the elimination of crude oil from seawater thanks to its efficient sorption capacity and low cost.

3D Printing High-Consistency Enzymatic Nanocellulose Obtained from a Soda-Ethanol-O2 Pine Sawdust Pulp

Soda-ethanol pulps, prepared from a forestry residue pine sawdust, were treated according to high-consistency enzymatic fibrillation technology to manufacture nanocellulose. The obtained nanocellulose was characterized and used as ink for three-dimensional (3D) printing of various structures. It was also tested for its moisture sorption capacity and cytotoxicity, as preliminary tests for evaluating its suitability for wound dressing and similar applications. During the high-consistency enzymatic treatment it was found that only the treatment of the O2-delignified pine pulp resulted in fibrillation into nano-scale. For 3D printing trials, the material needed to be fluidized further. By 3D printing, it was possible to fabricate various structures from the high-consistency enzymatic nanocellulose. However, the water sorption capacity of the structures was lower than previously seen with porous nanocellulose structures, indicating that further optimization of the material is needed. The material was found not to be cytotoxic, thus showing potential as material, e.g., for wound dressings and for printing tissue models.

New Composite Water Sorbents CaCl2-PHTS for Low-Temperature Sorption Heat Storage: Determination of Structural Properties

Sorption heat storage, as one of low-energy consuming technologies, is an approach to reduce CO2 emissions. The efficiency of such technology is governed by the performance of the applied sorbents. Thus, sorbents with high water sorption capacity and regeneration temperature from 80 to 150 °C are required. Incorporation of hygroscopic salt such as calcium chloride into porous materials is a logical strategy for increasing the water sorption capacity. This work reports the study on the development of composites with PHTS (plugged hexagonal templated silicate) matrix with an average pore size of 5.7 nm and different amounts of calcium chloride (4, 10, 20 wt.%) for solar thermal energy storage. These composites were prepared by wetness incipient impregnation method. Structural properties were determined by X-ray diffraction (XRD), nitrogen physisorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). CaCl2 was confined in micro- and mesopores of the matrix. The resulting CaCl2-PHTS materials were used for water sorption at 40 °C, showing an increase of maximal water uptake with higher amount of calcium chloride from 0.78 g/g to 2.44 g/g of the dry composite. A small reduction in water uptake was observed after 20 cycles of sorption/desorption between temperatures of 140 °C and 40 °C, indicating good cycling stability of these composites under the working conditions.

RESEARCH OF THE SWELLING KINETICS OF PINE WOOD, MODIFIED WITH AMINO-BORATES

Wood swells at the contact with capillary and liquid water. This process leads to premature destruction of wood material due to the decrease in its strength characteristics. It is possible to reduce wood swelling in various ways: deep impregnation by hydrophobic reagents, covering the surface with paints and varnishes etc. However, in this case the texture of wood is masked and its unique properties are lost. When modifying wood with amino-borates the supramolecular structure of cellulose is ordered, the specific surface of wood decreases, and its water sorption capacity is reduced. In this regard, we have researched the influence of boron-nitrogenous modifiers of various concentrations on pine wood swelling. The swelling ability of the modified wood was estimated by weight method. As a control sample the samples of unmodified wood were used. On the basis of the obtained experimental data the differential curves of swelling were built and the velocity constants of swelling were determined by a graphic method. As a result of the research it has been established that modifying wood with amino-borates leads to the decrease of equilibrium extent of swelling, and the velocity constant of swelling depends on the nature and concentration of the modifier and its influence on the microstructure of a wood composite.