Perspectives on the Lindman Hypothesis and cellulose interactions

In the history of cellulose chemistry, hydrogen bonding has been the predominant explanation when discussing intermolecular interactions between cellulose polymers. This is the general consensus in scholarly textbooks and in many research articles, and it applies to several other biomacromolecules’ interactions as well. This rather unbalanced description of cellulose has likely impacted the development of materials based on the processing of cellulose—for example, via dissolution in various solvent systems and regeneration into solid materials, such as films and fibers, and even traditional wood fiber handling and papermaking. In this review, we take as a starting point the questioning of the general description of the nature of cellulose and cellulose interactions initiated by Professor Björn Lindman, based on generic physicochemical reasoning about surfactants and polymers. This dispute, which became known as “the Lindman hypothesis”, highlights the importance of hydrophobic interactions in cellulose systems and that cellulose is an amphiphilic polymer. This paper elaborates on Björn Lindman’s contribution to the subject, which has caused the scientific community to revisit cellulose and reconsider certain phenomena from other perspectives.info:eu-repo/semantics/publishedVersio

Fundamental Characterization and Technical Aspects of a Chelating Surfactant

The purpose of this study was to investigate the fundamental characteristics of a chelating surfactant in terms of solution behaviour, chelation of divalent metal ions, and interaction in mixtures with different foaming agents and divalent metal ion, as well as examining its prospects in some practical applications. Chelating surfactants are functional molecules, with both surface active and chelating properties, which are water soluble and therefore suitable for chelation in many aqueous environments. The dual functionality offers the possibility to recover the chelating surfactant as well as the metals. The DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 4-C12-DTPA (2-dodecyldiethylenetriaminepentaacetic acid) was synthesized at Mid Sweden University. In the absence of metal ions, all eight donor atoms in the headgroup of 4-C12-DTPA are titrating and the headgroup charge can be tuned from +3 to -5 by altering the pH. The solution properties, studied by surface tension measurements and NMR diffusometry, were consequently found strongly pH dependent. pH measurements of chelating surfactant solutions as a function of concentration was used to extract information regarding the interaction between surfactants in the aggregation process. Small differences in the conditional stability constants (log K) between coordination complexes of DTPA and 4-C12-DTPA, determined by competition measurements utilizing electrospray ionization mass spectrometry (ESI-MS), indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. This was further confirmed in hydrogen peroxide bleaching of thermomechanical pulp (TMP) treated with 4-C12-DTPA. Interaction parameters for mixed systems of 4-C12-DTPA and different foaming agents were calculated following the approach of Rubingh’s regular solution theory. The mixtures were also examined with addition of divalent metal ions in equimolar ratio to the chelating surfactant. Strong correlation was found between the interaction parameter and the phase transfer efficiency of Ni2+ ions during flotations. Furthermore, a significant difference in log K between different metal complexes with 4-C12-DTPA enabled selective recovery of the metal ion with the highest log K. The findings in this study contribute to the understanding of the fundamental characteristics of chelating surfactants, which can be further utilized in practical applications

Kvinnor duger men våld "suger" : Ungdomars attityder till den svenska polisen

Forskning har visat att människor i allmänhet har positiva attityder till polisen. Syftet med denna studie var att undersöka ungdomars attityder till den svenska polisen. Det undersöktes om polisens olika grad av våldsamt agerande påverkade deltagarnas uppfattningar och om attityderna skilde sig gentemot kvinnliga respektive manliga ordningspoliser. En egenkonstruerad enkät innehållande fyra olika berättelser delades ut i tre gymnasieskolor. Deltagarna var 88 unga kvinnor och 42 unga män som studerade på föreläsningsbaserade program. Resultatet visade att de flesta deltagare hade en positiv attityd. Resultatet visade även att ju mer våldsamt agerande desto mindre professionell, hänsynstagande och mer känslostyrd uppfattades polisen som. Det fanns inte någon skillnad mellan attityderna till kvinnliga respektive manliga poliser. För hänsynstagande och affekt visade dock resultatet en tendens till en interaktionseffekt mellan polisens kön och våldsamhet. Detta kan bero på att det fortfarande kan finnas stereotypa könsuppfattningar hos deltagarna för vissa attribut hos polisen

Impact of the Amphoteric Nature of a Chelating Surfactant on its Interaction with an Anionic Surfactant: A Surface Tension and Neutron Reflectivity Study of Binary Mixed Solutions

2-Dodecyldiethylenetriaminepentaacetic acid (C12-DTPA) is a chelating, amphoteric surfactant with a bulky headgroup containing eight pH-responsive groups. The hypothesis was that the amphoteric nature of the chelating surfactant would affect the interaction with another surfactant and, consequently, also the composition of mixed surface layers. Binary mixed monolayers of C12-DTPA and the anionic surfactant sodium dodecyl sulfate (SDS) were examined using neutron reflection and surface tension measurements. The experiments were conducted at pH 5, where the C12-DTPA monomers carried a net negative charge. Surface excess calculations at low total surfactant concentration revealed that the chelating surfactant dominated the surface composition. However, as the concentration was raised, the surface composition shifted toward an SDS-dominant state. This phenomenon was attributed to the increased ionic strength at increased concentrations, which altered the balance between competing entropic forces in the system. Interaction parameters for mixed monolayer formation were calculated, following a framework based on regular solution theory. In accordance with the hypothesis, the chelating surfactant’s ability to modulate its charge and mitigate repulsive interactions in the surface layer resulted in favorable interactions between the anionic SDS and negatively charged C12-DTPA monomers. These interactions were found to be concentration-dependent, which was consistent with the observed shift in the surface layer composition

On Structural and Molecular Order in Cellulose Acetate Butyrate Films

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

Tuning the properties of regenerated cellulose: Effects of polarity and water solubility of the coagulation medium

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 [GRAPHICS]KK Foundation (Sweden)Nouryon (Sweden)info:eu-repo/semantics/publishedVersio

Anomalies in Solution Behavior of an Alkyl Aminopolycarboxylic Chelating Surfactant

The solution behavior of a DTPA (diethylenetriamine pentaacetic acid)-based chelating surfactant, 4-C₁₂-DTPA, has been studied by tensiometry and NMR diffusometry. In the absence of metal ions, the eight donor atoms in the headgroup are titrating, and the charge of the headgroup can thus be tuned by altering the pH. 4-C₁₂-DTPA changes from cationic at very low pH, over a number of zwitterionic species as the pH is increased, and eventually becomes anionic at high pH. Around the isoelectric point, the chelating surfactant precipitated. The solution properties, studied above the solubility gap, were found strongly pH dependent. When increasing the amount of negative charges in the headgroup, by increasing the pH, the adsorption efficiency was reduced and the cmc was increased. An optimum in surface tension reduction was found at pH 5, due to a proper balance between protonated and dissociated groups. Anomalies between surface tension measurements and NMR diffusometry in determination of cmc revealed a more complex relation between surface tension, surface coverage, and cmc than usually considered, which is not in line with the common interpretation of the Gibbs adsorption equation. At some of the investigated pH levels, measurements of bulk pH could confirm the location of cmc, due to the increased protonation of micelles compared to monomers in solution. The adsorption of monomers to the air–water interface showed unusually slow time dependence, evident from decreasing surface tension for several hours. This is explained by rearrangements of the large head groups to reduce the headgroup area and increase the packing parameter

Lignina aumenta a dissolução de celulose em álcali fria

Aqueous sodium hydroxide solutions are extensively used as solvents for lignin in kraft pulping. These are also appealing systems for cellulose dissolution due to their inexpensiveness, ease to recycle and low toxicity. Cellulose dissolution occurs in a narrow concentration region and at low temperatures. Dissolution is often incomplete but additives, such as zinc oxide or urea, have been found to significantly improve cellulose dissolution. In this work, lignin was explored as a possible beneficial additive for cellulose dissolution. Lignin was found to improve cellulose dissolution in cold alkali, extending the NaOH concentration range to lower values. The regenerated cellulose material from the NaOH-lignin solvents was found to have a lower crystallinity and crystallite size than the samples prepared in the neat NaOH and NaOH-urea solvents. Beneficial lignin-cellulose interactions in solution state appear to be preserved under coagulation and regeneration, reducing the tendency of crystallization of cellulose.info:eu-repo/semantics/publishedVersio