A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

Biodegradable composites based on lignocellulosic fibers—An overview

We report a study of self-assembled beta-pleated sheets in B. mori silk fibroin films using thermal analysis and infrared spectroscopy. B. mori silk fibroin may stand as an exemplar of fibrous proteins containing crystalline beta-sheets. Materials were prepared from concentrated solutions (2−5 wt % fibroin in water) and then dried to achieve a less ordered state without beta-sheets. Crystallization of beta-pleated sheets was effected either by heating the films above the glass transition temperature (Tg) and holding isothermally or by exposure to methanol. The fractions of secondary structural components including random coils, alpha-helices, beta-pleated sheets, turns, and side chains were evaluated using Fourier self-deconvolution (FSD) of the infrared absorbance spectra. The silk fibroin films were studied thermally using temperature-modulated differential scanning calorimetry (TMDSC) to obtain the reversing heat capacity. The increment of the reversing heat capacity ΔCp0(Tg) at the glass transition fo...

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Determining Beta Sheet Crystallinity in Fibrous Proteins by Thermal Analysis and Infrared Spectroscopy

Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

Trees, and their derivative products, have been used by societies around the world for thousands of years. Contemporary construction of tall buildings from timber, in whole or in part, suggests a growing interest in the potential for building with wood at a scale not previously attainable. As wood is the only significant building material that is grown, we have a natural inclination that building in wood is good for the environment. But under what conditions is this really the case? The environmental benefits of using timber are not straightforward; although it is a natural product, a large amount of energy is used to dry and process it. Much of this can come from the biomass of the tree itself, but that requires investment in plant, which is not always possible in an industry that is widely distributed among many small producers. And what should we build with wood? Are skyscrapers in timber a good use of this natural resource, or are there other aspects of civil and structural engineering, or large-scale infrastructure, that would be a better use of wood? Here, we consider a holistic picture ranging in scale from the science of the cell wall to the engineering and global policies that could maximise forestry and timber construction as a boon to both people and the planet.

The wood from the trees: The use of timber in construction

Cellulose nanofibre sheet materials are of great interest in various applications because of their excellent properties, but are difficult to prepare rapidly and as large sheets. This paper describes a quick preparation procedure for preparing optically transparent, flat and smooth nanofibre sheets, which is much quicker than existing methods. Low permeability, optical transparency, high strength and high density show that nanofibres were well dispersed. The preparation time for the nanofibre sheet produced here was 10 min whereas the preparation times reported in literature is above 1 h. The decrease in sheet preparation time suggests that this method can be used for commercial applications.

Rapid preparation of cellulose nanofibre sheet

Nanocellulose has great potential for end use in the pulp and paper industry, but its mechanical production process is often extremely energy intensive. Although various pre-treatment methods have been introduced to significantly lower the energy consumption of nanocellulose production, there still remains a great challenge to match the cost to mechanical strength performance of nanocellulose. This research investigates the relationship between energy consumption with numerous refining and homogenization cycles towards the production of high aspect ratio and low diameter nanocellulose, and whether this is necessary to achieve high strength sheets. Never-dried Bleached Eucalyptus Kraft pulp was mechanically treated with a PFI mill refiner and homogenizer. The actual homogenization energy measured on a lab scale was significantly higher than that predicted only from the simplified pressure drop equation which is inaccurately independent of homogenizer design and size. We measured two aspects of fiber quality believed to be related to sheet mechanical strength: the fiber diameter, which is inversely proportional to the surface area available for bonding, and the fiber aspect ratio, which is believed to control the efficiency of stress transfer within a network. Both refining and homogenization reduced the fiber diameter and increased the aspect ratio, but homogenization was more effective at both. There was surprisingly little correlation between the measures of fiber quality and mechanical sheet strength. All PFI mill refined samples had a tensile index of around 100 Nm/g, while additional treatment with homogenization increased this only by approximately 20%. This was despite the most heavily treated fibers (50,000 PFI revolutions and 3 homogenization passes at 1000 bar) having a median diameter of 12 nm and aspect ratio of 229 compared to the least treated fibers (10,000 PFI revolutions) with a median diameter of 31 nm and aspect ratio of 102. The most heavily treated fibers required 39,000 kWh/t of energy, a tenfold increase over the least heavily treated fibers. The results confirmed that there was small benefit, in terms of mechanical strength, of using very large amounts of energy to produce very low diameter, high aspect ratio nanocellulose fibers.

Effect of refining and homogenization on nanocellulose fiber development, sheet strength and energy consumption

Novel water resistant photocatalytic composites of microfibrillated cellulose (MFC)—polyamide-amine-epichlorohydrin (PAE)—TiO2 nanoparticles (NPs) were prepared by a simple two-step mixing process. The composites produced are flexible, uniform, reproducible and reusable; they can readily be removed from the pollutant once used. Small amount of TiO2 NPs are required for the loaded composites to exhibit a remarkable photocatalytic activity which is quantified here as achieving at least 95% of methyl orange degradation under 150 min of UV light irradiation for the composite with best combination. The cellulose network combined with PAE strongly retains NPs and hinders their release in the environment. PAE dosage (10 and 50 mg/g MFC) controls the NP retention in the cellulose fibrous matrix. As TiO2 content increases, the photocatalytic activity of the composites levels off to a constant; this is reached at 2wt% TiO2 NPs for 10 mg/g PAE and 20wt% for 50 mg/g PAE. SEM and SAXS analysis confirms the uniform distribution of NPs and their formation of aggregates in the cellulose fibre network. These economical and water resistant photocatalytic paper composites made by a simple, robust and easily scalable process are ideal for applications such as waste water treatment where efficiency, reusability and recyclability are important.

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Water Resistant Cellulose - Titanium Dioxide Composites for Photocatalysis.

A cellulose nanofibre aerogel filter with tuneable pore structure exhibiting super-hydrophilic and underwater-super-oleophobic behaviours is synthesized by a facile method of cross-linking between cellulose nanofibres and polyamideamine-epichlorohydrin (PAE). The prepared aerogel filter showed excellent oil/water separation efficiency for both oil/water mixtures (100%, even after 10 cycles), and oil/water surfactant-free emulsion (98.6%), which is driven solely by gravity. In addition, the specific structure can de-emulsify oil/water emulsion. The results showed that the cellulose aerogel filter can be used for oil/water separation and recovery.

Cellulose nanofibre aerogel filter with tuneable pore structure for oil/water separation and recovery

Spraying of nanocellulose (NC) on a solid surface to prepare films is an alternative technique to vacuum filtration, which requires a long drainage time and produces films which can sometimes be difficult to separate from the filter. This letter reports a rapid preparation technique for nano-cellulose films using a bench scale system spray coating nanocellulose suspension onto stainless steel plates. After spraying NC suspension onto a smooth steel plate travelling on a constant velocity conveyor, the films can be dried directly on the plates using standard laboratory procedures, saving processing time and effort. By adjusting the suspension consistency, we were able to reproducibly make films with a basis weight ranging from 52.8 ± 7.4 to 193.1 ± 3.4 g/m2 when spraying on to a plate moving at a velocity of 0.32 cm/s. The operator preparation time for the nanocellulose film was 1 min, independent of the sample basis weight, which compares to production times reported in the literature of 10 min using filtration techniques. The films made by spray coating showed higher thickness, but comparable uniformity, to those made by vacuum filtration. Optical profilometry measurements showed that over a 1 cm × 1 cm inspection area that the surface roughness (RMS) of the NC film is only 389 nm on the spray coated side in contact with the steel plates, compared to 2087 nm on the outside surface. Thus, the reduction in preparation time for producing the nanocellulose film recommends this spray coating technique as a rapid and flexible method to produce NC films at the laboratory scale.

Warren Batchelor

Papers

Rapid preparation of cellulose nanofibre sheet

Effect of refining and homogenization on nanocellulose fiber development, sheet strength and energy consumption

Water Resistant Cellulose - Titanium Dioxide Composites for Photocatalysis.

Cellulose nanofibre aerogel filter with tuneable pore structure for oil/water separation and recovery

Rapid preparation of smooth nanocellulose films using spray coating