| 1. |
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| 2. |
- Engqvist, Cecilia, et al.
(författare)
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Interactions between single latex particles and silica surfaces studied with AFM
- 2007
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 302:03-jan, s. 197-203
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Tidskriftsartikel (refereegranskat)abstract
- The spreading of single styrene-acrylic latex particles on silicon oxide C surfaces was studied using atomic force microscopy (AFM). Three latexes with different glass transition temperature (Tg) were used and the effects of temperature, time and preparation method were investigated. Particle sizes and shape were measured with AFM and the contact angles were calculated. The observed rate for the spreading of latex particles was low and it took several days before the particles reached steady state, even at temperatures well above their T-g. The experimental particle spreading results deviated with two orders of magnitude from predictions Using the WLF equation for polymer diffusion. The deviation could be attributed to polymer-surface interactions that slowed down the particle spreading. The work of adhesion was calculated using two models. The results from using the regular Young-Dupre equation and a modified version of this equation that also included the mechanical properties (E-modulus and Poisson's ratio) of the latexes, were compared. For soft latex particles the results from the two models agreed well and were of the order of 75 J/m(2), but for glassy latexes the Young-Dupre equation underestimated the work of adhesion.
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| 3. |
- Halvarsson, Sören, et al.
(författare)
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Manufacture of High-Performance Rice-Straw Fiberboards
- 2010
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 49:3, s. 1428-1435
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Tidskriftsartikel (refereegranskat)abstract
- Rice straw, a waste agriculture material grown and harvested in Willows, CA, was used,is a raw material in the production of thin medium- and high-density fiberboards (MDFs and HDFs). The rice straw was cleaned, size-reduced, and soaked in water before being refined. Defibration was performed in it pressurized pilot-plant single-disk refiner, OHP 20". The fiber production capacity reached a level of 63 kg/h. and the proper fiber quality for MDF/HDF production was established. Analysis of the produced fiber showed an average fiber length of approximately 0.9 mm, in average fiber width of 31 mu m, a shive weight of below 24%, and a dust content of less than 30%. Production of fiberboards was performed by addition of 3%, 4%, and 5% methylene diphenyl diisocyanate (MDI). The flexural properties, internal bond strength, and thickness swelling of the produced fiberboards were evaluated according to ASTM methods. The finished fiberboards based on rice straw and MDI resin showed excellent properties. The internal bond (IB) reached levels of 2.6 MPa, and the modulus of rupture (MOR) and modulus of elasticity (MOE) showed levels comparable to those of wood-based fiberboards and were acceptable according to the requirements or medium-density fiberboard (MDF) for interior applications (American National Standards Institute, ANSI A208.2-2002). The water-repelling properties of the 3-min rice-straw fiberboards were encouraging; the thickness swelling, (TS) was in the range of 15-30%. Two different methods to avoid adhesion between the press plates and the resinated fiber material during hot pressing were investigated: protective paper sheets were placed between the fiber mat and press plates, or a press-release agent was sprayed oil steel plates that were then placed ill the press before pressing Satisfactory results were obtained with both methods, and no adhesion was observed between the fiberboard and the steel plates. The method of using press-release agent during pressing had no notable negative effects oil the fiberboard properties.
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| 4. |
- Halvarsson, Sören, et al.
(författare)
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Manufacture of non-resin wheat straw fibreboards
- 2009
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Ingår i: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 29:2-3, s. 437-445
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Tidskriftsartikel (refereegranskat)abstract
- Wheat straw was used as raw material in the production of fibreboards. The size-reduced straw was pretreated with steam, hot water and sulphuric acid before the defibration process to loosen its physical structure and reduce the pH. No synthetic binder was added. Adhesive bonding between fibres was initiated by activation of the fibre surfaces by an oxidative treatment during the defibration process. Fenton's reagent (ferrous chloride and hydrogen peroxide) was added. Two different levels of hydrogen peroxide (H2O2), 2.5% or 4.0% were used. The resulting fibres were characterized in terms of fibre length distribution, shive content, pH and pH-buffering capacity. The properties of finished fibreboards were compared with medium-density fibreboard (MDF) with density above 800 kg/m(3) produced from straw and melamine modified UF resin. The modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond (IB) were lower than those of conventional manufactured wheat straw fibreboards but close to the requirements of the MDF standard (EN 622-5: 2006). The water absorption properties for the H2O2 activated straw fibreboards were relatively high, but were reduced by 25% with the addition of CaCl2 into the defibrator system as a water-repelling agent. Increased levels of hydrogen peroxide improved the mechanical and physical properties of the straw fibreboard. Crown
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| 5. |
- Halvarsson, Sören, et al.
(författare)
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Properties of Medium Density Fibreboard (MDF) based on Wheat straw and Melamine Modified Urea Formaldehyde (UMF) Resin
- 2008
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Ingår i: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 28:1, s. 37-46
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Tidskriftsartikel (refereegranskat)abstract
- Wheat straw was investigated as a raw material for manufacturing of medium density fibreboard (MDF) in a fully equipped pilot-plant. Commercial urea melamine formaldehyde (UMF) and a mixture of UMF-resin and urea melamine phenol formaldehyde (UMPF) adhesives were used as binders in manufacturing of high performance MDF. The study evaluated the quality of MDF produced of straw (i.e., SMDF). Different qualities of wheat straw and different resin contents (14–17%) were used. Moreover, the SMDF was produced at different thicknesses of 9 and 16 mm and densities of 750–1000 kg/m3. The properties of the resulting SMDF were evaluated by analysing mechanical and water absorption (anti-swelling) properties as a function of density. Internal bond (IB), modulus of rupture (MOR), modulus of elasticity (MOE), thickness swelling (TS), and water absorption (WABS) were the properties analysed. SMDF-panels produced with densities above 780 kg/m3 and resin contents above 14% met the requirements for wood-based MDF standard EN 622-5:1997.
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| 6. |
- Högberg, Hans-Erik, et al.
(författare)
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Biocatalysis as a useful tool in pheromone synthesis. Enantiomerically pure building blocks from baker's yeast reductions and enzyme catalysed resoluti
- 1994
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 22:3, s. 591-606
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Tidskriftsartikel (refereegranskat)abstract
- Biocatalytical methods are presented which provide useful building blocks for pheromone synthesis. Examples of the utility of this approach are the preparation of building blocks for the synthesis of stereochemically pure isomers of pine sawfly pheromones and some other pheromones. Enantiom- erically pure ( 98% ee) 2-methyl-1-alkanols 2 were obtained via baker's yeast reduction of suitable α,β-unsaturated aldehydes, and by using lipases from Pseudomonas to effect resolution by transesterification of suitable racemic precursors to 2-methyl-1-alkanols 2 which gave high enantiomeric ratios E > 100. The resolution by esterification mediated by lipase from Candida rugosa of racemic 2-methylalkanoic acids also gave high enantiomeric ratios E> 100 after having improved the reaction conditions by regulating water activity, by choice of the appropriate complimentary substrate alcohol and by adjusting the initial equivalents of the latter present at the start. Also discussed is the separation of diastereomers of diprionol 1, which is naturally occurring in the pine sawfly Neodiprion sertifer, where it is the direct precursor of its pheromone.
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| 7. |
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| 8. |
- Lidenmark, Cecilia, 1976-, et al.
(författare)
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The adhesive behavior of extracted latex polymers towards silicon oxide and cellulose
- 2013
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Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier. - 0143-7496 .- 1879-0127. ; 44, s. 250-258
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Tidskriftsartikel (refereegranskat)abstract
- The objective with this work is to compare the adhesive behavior for latex polymers of different glass transition temperatures (T-g) at different length scales and with different contact times. This is accomplished by two techniques: AFM colloidal probe force measurements and JKR-measurements. The aim is to compare the results from these two techniques and relate them to the interaction of the latex polymers towards oxidized silicon wafers and silica/cellulose probes. Theory suggests that altering the short timeframes used in the colloidal probe technique does not affect the ranking of the adhesion for the different polymers, but for the macroscopic JKR-technique it influences the measured work of adhesion. It is therefore important to let the system reach a steady state before assuming complete spreading and adhesion. AFM and JKR measurements showed the same trends where the polymer with lowest content of styrene has the lowest T-g and the highest adhesion, due to the larger polymer chain mobility.
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| 9. |
- Nejström, Malin, et al.
(författare)
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On Structural and Molecular Order in Cellulose Acetate Butyrate Films
- 2023
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 15:9
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Norgren, Magnus, et al.
(författare)
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Aggregation of Kraft Lignin Derivatives under Conditions Relevant to the Process. Part I. Phase Behaviour
- 2001
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 194:1-3, s. 85-96
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Tidskriftsartikel (refereegranskat)abstract
- Aggregation of a commercial, polydisperse softwood kraft lignin (Indulin AT) in diluted aqueous alkaline solutions was investigated experimentally, by means of turbidity measurements. The influence of temperature, salt concentration and pOH and the role of a divalent counterion on the aggregation behaviour were studied. When the temperature was increased, an increased tendency of aggregation in samples containing high concentrations of sodium chloride was found. Phase separation could be detected even at pOH=2 at 175°C and the effect was pronounced when the concentration of hydroxide ions decreased. The phase transition from soluble to precipitated lignin was found to be irreversible concerning temperature change. Small amounts of calcium ions were seen to induce dramatic effects on the system stability, even at relatively high hydroxide concentrations (pOH 1-2). At a given temperature and pOH, the coagulation was found to appear at a certain critical coagulation concentration (CCC) of the added electrolyte. Furthermore, calculations were carried out to compare with the outcome of the experimental observations. A theoretical model, based on the DLVO theory, was found to predict the kraft lignin solution behaviour well.
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