This work describes an emulsification-solvent-evaporation method for the preparation of liquid-filled capsules made from cellulose acetate. Two different emulsification techniques were applied: bulk emulsification by high-shear mixing, and droplet generation using microfluidics. The bulk emulsification method resulted in the formation of oil-in-water emulsions composed of an organic mixture of isooctane and cellulose acetate in methyl acetate, and an aqueous phase of high-molecular-weight polyvinyl alcohol (PVA). Upon the solvent evaporation, the emulsion droplets evolved into isooctane-filled cellulose acetate capsules. In contrast, microfluidics led to the formation of monodisperse droplets composed of the aqueous PVA solution dispersed in the organic phase. Upon the solvent evaporation, the emulsion droplets evolved into water-filled cellulose acetate capsules. Owing to the thermoplastic properties of the cellulose acetate, the capsules formed with the bulk mixing demonstrated a significant expansion when exposed to an increased temperature. Such expanded capsules hold great promise as building blocks in lightweight materials.

Cellulose acetate butyrate (CAB) is a possible candidate, being a raw material derived from renewable resources, to replace fossil-based materials. This is due to its thermoplastic properties and the relative ease with which it could be implemented within the existing industry. With a significant amount of variation in CAB on the market today, a knowledge gap has been identified regarding the understanding of the polymer structural arrangement in films. This relates to the underlying mechanisms that regulate CAB film material properties, insights that are important in product development. In this study, commercially available CAB was investigated with XRD, SEM, AFM, and TOPEM DSC in order to obtain physicochemical information related to its micro-structural features in solvent-cast films. The film-forming ability relates mostly to the number of hydroxyl groups, and the semi-crystallinity of the films depends on the type and position of the side groups along the cellulose backbone. The appearance of signs of possible cholesteric ordering in the films could be connected to higher amounts of hydroxyl groups along the backbone that disturb the helix arrangement, while the overall order was primarily related to the butyrate substitution and secondarily related to the molecular weight of the particular CAB studied. Cold crystallization was also observed in one CAB sample.

In this study, the effect of different alcohols and esters as a coagulation medium in the regeneration of cellulose dissolved in an aqueous LiOH-urea-based solvent was thoroughly investigated using various methods such as solid state NMR, X-ray diffraction, water contact angle, oxygen gas permeability, mechanical testing, and scanning electron microscopy. It was observed that several material properties of the regenerated cellulose films follow trends that correlate to the degree of cellulose II crystallinity, which is determined to be set by the miscibility of the coagulant medium (nonsolvent) and the aqueous alkali cellulose solvent rather than the nonsolvents' polarity. This article provides an insight, thus creating a possibility to carefully tune and control the cellulose material properties when tailor-made for different applications.

Influence of regeneration liquid polarity on different material properties of dried cellulose II films

The properties of the materials combined in corrugated board are set to give the board its strength, flexibility and protection towards impact and pressure. The raw material is of course the single fibre but additives that enhance e.g. the wet and dry paper strength are also added. As the strength enhancing additives used today are most efficient between pH 4 and pH 7 there is a need for new types of additives that can be used under alkaline conditions. In the present report polyallylamine hydrochloride (PAH) and polyelectrolyte complexes (PEC) of PAH and polyacrylic acid (PAA) were investigated as strength enhancing additives. The components can be used under alkaline conditions and results showed that PAH alone or incorporated into a PEC gave different effects regarding strength properties of sheets from kraft pulps of different yields. The results showed that by treating the fibres with PEC's of PAH and PAA it was possible to considerably increase the tensile properties, the Z-strength and the compression strength of papers made from the treated fibres. The results showed an increase of as much as 54 % to 180 % in dry Z-strength and 14 % to 53 % in compression strength, when using the PEC as an additive, indicating an increase in inter-fibre joint strength. It was also found that a heat treatment of the non-treated papers and of the papers from the PAH treated fibres gave a large improvement in tensile properties as well as Z-strength properties for the different pulps. For the PLC treated fibres it was not necessary to heat-treat the paper to achieve a higher dry strength. The molecular mechanism behind the large improvements is not identified in the present work but the problem is currently being investigated in the lab of the authors.

The influence of pore structure and the water retaining ability of fibres on different strength properties of papers from unbleached kraft fibres was investigated and the effects of pulp yield, counter-ion types, pH and homification were determined. NMR relaxation measurements of water were used to determine the pore structure of the fibres and WRV and FSP measurements were used to determine their water retaining ability. The average pore radius, as determined by NMR, was almost unaffected by changes in pulp yield whereas changes in counter-ion and pH had a significant effect on the average pore radius. The detected changes in NMR were suggested to be due to changes in the swelling forces both within the fibre wall and at the fibre surface. The WRV value decreased with decreasing yield and it was significantly affected by pH and counter-ion. Changes in WRV were explained to be largely associated with changes in the amount of water associated with the fibre surface. The FSP values decreased with decreasing yield just as the WRV's. Homification upon drying and reslushing significantly lowered the average pore radius, whereas the FSP only showed a minor decrease, suggesting that the surface area available to water was changed without drastically changing the overall fibre wall volume. The differences between FSP NMR and WRV can hence be traced back to what the methods are actually measuring. It was concluded that the different measuring methods contain unique information and that a combination of the methods is necessary to give as complete a picture as possible over the changes that occur in the fibre wall upon varying the condition for the fibres. The influence of pore size on sheet tensile properties was also investigated. It was found that fibres with larger pores produced an increased tensile index and tensile stiffness of the paper made from these fibres. It was suggested that fibres with larger pores allow for a larger molecular contact area between fibres, stronger fibre/fibre joints and consequently a higher strength of the formed sheets.

It has been shown, in the present investigation, that the two methods used to investigate the pore size distribution of unbleached chemical pulps, i.e. inverse size exclusion chromatography (ISEC) and nuclear magnetic resonance (NMR), give different average pore radius for the pores inside the fibre wall. This is due to the way in which these experiments are performed and the sensitivity of the methods to different types of pores in the cell wall. It was also shown that the two methods gave different results when changing the pH and the ionic strength of the pulp suspension. The pore radius, as detected with ISEC, decreased with both increasing ionic strength and decreasing pH, indicating a loose structure of the exterior of the fibrillar network. However, the pore radius as detected with NMR, was virtually unaffected when increasing the ionic strength, indicating a very rigid structure of the interior of the fibre wall. Decreasing pH though, lead to a decrease in pore radius indicating that upon protonation of the carboxylic groups in the fibre wall, the electrostatic repulsion is diminished and the average pore radius decreases. The NMR technique was also used to study wet strength aid penetration into the fibre wall. It was shown that wet strength aids with a small molecular weight, penetrated the fibre wall, as detected by a decrease in pore radius. It was also shown that addition of different wet strength aids increased the tensile index of the sheet and decreased the fibre strength, measured as zero span-strength of the sheets.

The porous structure of the interior of papermaking fibres is a well-known important property of the fibres. Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall. Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking. In this paper, pore sizes and the pore size distribution of unbleached softwood fibres have been studied. A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used. Pore size and pore size distribution were measured by studies of the relaxation behaviour of 2 H in fibres saturated with 2 H 2 O. Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres. For both pulps, there is a maximum in pore radius at a yield around 46%. Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51%. It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/lignin matrix within the fibre wall at this yield level. The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres. Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall. This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall.