Tuula T. Pakkanen

Phenol‐formaldehyde resol resins studied by 13C‐NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry

A series of phenol-formaldehyde resins was produced in the presence of NaOH catalyst. Detailed structural and quantitative information was provided by 13C-NMR spectroscopy. The main interests were the relative quantities of bridge structures, methylol groups, and free phenol. Functionality and linearity of resins were also studied. The effects of the condensation F/P molar ratio on the structure and properties of the resins was studied by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) in addition to 13C-NMR.

IR spectroscopy as a quantitative and predictive analysis method of phenol–formaldehyde resol resins

A set of resin samples was characterized by IR and 13C-NMR spectroscopy. The suitability of IR spectroscopy for the quantitative analysis of resins was evaluated by statistical methods using the NMR reference data as calibration. The values of interesting properties, for example, the amount of free phenol and the formaldehyde-to-phenol (F/P) molar ratio, of the resins being similar to the calibration resins were predicted from the IR spectra. Also, the predicted results were compared with the ones observed by 13C-NMR spectroscopy.

Acidic properties of ZSM-5 zeolite modified with Ba2+, Al3+ and La3+ ion-exchange

Abstract The acidity of a ZSM-5 zeolite was modified with Ba2+, Al3+ and La3+ ion-exchange. The ion-exchange process was repeated three times and after each ion-exchange cycle the samples were calcined. The acidity of the modified zeolites was characterized by IR and MAS NMR spectroscopy. The number of strong Bronsted acid sites decreases rapidly with increasing degree of barium ion-exchange since the effect of Plank-Hirschler mechanism is quite negligible due to the relatively low electrostatic potential of Ba2+ cations. However, the splitting of water molecules resulting in the formation of new Bronsted acid sites and acidic M(OH)2+2 groups is more probable in La3+ and Al3+ ion-exchanged zeolites. The formation of new Bronsted acid sites was observed in the IR spectra of highly Ba2+ exchanged zeolite after the chemisorption of pyridine. This may be due to the formation of pyridinium ions via the reaction of base pyridine with unsplitted water molecules coordinated to Ba2+ ions. The catalytic activity of the modified zeolites was measured in an n-hexane cracking reaction. Zeolites with a high degree of Al3+ and La3+ ion-exchange were found to be slightly more active than unmodified zeolite, in accordance with the formation of new acid sites. The aluminium and lanthanum ion-exchange enhanced slightly the formation of C5 and olefinic products and decreased the formation of C3 and aromatic products.

Mechanically Robust Superhydrophobic Polymer Surfaces Based on Protective Micropillars

Considerable attention is currently being devoted less to the question of whether it is possible to produce superhydrophobic polymer surfaces than to just how robust they can be made. The present study demonstrates a new route for improving the mechanical durability of water-repellent structured surfaces. The key idea is the protection of fragile fine-scale surface topographies against wear by larger scale sacrificial micropillars. A variety of surface patterns was manufactured on polypropylene using a microstructuring technique and injection molding. The surfaces subjected to mechanical pressure and abrasive wear were characterized by water contact and sliding angle measurements as well as by scanning electron microscopy and roughness analysis based on optical profilometry. The superhydrophobic polypropylene surfaces with protective structures were found to maintain their wetting properties in mechanical compression up to 20 MPa and in abrasive wear tests up to 120 kPa. For durable properties, the optimal surface density of the protective pillars was found to be about 15%. The present approach to the production of water-repellent polymer surfaces provides the advantages of mass production and mechanical robustness with practical applications of structurally functionalized surfaces.

Conformational behaviour of hydroxamic acids: ab initio and structural studies

The conformational behaviour of a series of monohydroxamic acids, p-RC6H4CONR′OH (R = Me, R′= H, Me; R = MeO, R′= H, Me; R = NO2, R′= H), and a series of dihydroxamic acids, (CH2)n(CONR′OH)2(n= 3–8, 10, R′= H and n= 7, R′= Me), in methanol, DMSO and chloroform and in the solid state has been examined using IR and NMR spectroscopy. X-Ray crystal structure determinations of p-MeC6H4CONMeOH and the monohydrate of glutarodihydroxamic acid (n= 3) together with ab initio molecular orbital calculations for several hydrated and unhydrated hydroxamic acids have been performed. Hydrogen bonding effects are shown to be important in both the solid state and solution. The cis(Z) conformation of the hydroxamate group(s)(CONHOH) is preferentially stabilized by hydrogen bonding with water molecules.

Phenolic compounds in silver birch (Betula pendula Roth) wood

Abstract Three new phenolic compounds (4-hydroxy-2-methoxyphenyl-6-O-syringoyl-β-D-glucopyranoside, 2-hydroxy-4-methoxyphenyl-6-O-syringoyl-β-D-glucopyranoside, and 4-hydroxymethyl-2-methoxyphenyl-6-O-syringoyl-β-D-glucopyranoside) and 15 known phenolic compounds (two phenyl glucoside esters, five lignans, three diarylheptanoids and five simple aldehydes or ketones) were isolated from the secondary xylem of mature Betula pendula Roth. The compounds were identified on the basis of their NMR (1D and 2D) and mass spectral data. In total, 23 phenolic extractives present in the sapwood of two winter-dormant B. pendula trees felled at different growing sites (rich in nutrients and scarce in nutrients) were quantified by GC. Their amounts were mostly low, 0.01–0.18 mg g−1 of dry wood. Total amounts of the phenolic extractives isolated were 1.2 mg g−1 of dry wood (5.6% of the total methanol-soluble extractives) in the tree felled at the site rich in nutrients, and 1.9 mg g–1 of dry wood (10% of the total methanol-soluble extractives) in the tree felled at the site scarce in nutrients.

CIEL*a*b* Measurements to Determine the Role of Felling Season, Log Storage and Kiln Drying on Coloration of Silver Birch Wood

The effects of felling season, log storage and kiln drying on stemwood discoloration of sixty mature silver birches ( Betula pendula ) were studied and provided with CIEL*a*b* colour coordinates. The colour differences were expressed as j E* including split up of j L*, j a* and j b*. The results showed that fresh wood colour depends on the felling season: light and pale colours were recorded for samples taken from autumn- and winter-felled trees, whereas the colour of fresh wood was considerably darker if the felling took place in the spring or summer. After storage, notable changes in colour were observed. After drying, all samples showed low lightness, moderate redness and relatively high yellowness under the drying conditions used in the study regardless of the felling season or duration of storage. The main colour component responsible for the discoloration was lightness, while chroma values redness and yellowness played a minor role.

Immobilization of metal chloride complexes of titanium, zirconium, and hafnium on a cyclopentadienyl surface of silica for ethylene polymerization

Abstract Metal chloride complexes, MCl4(THF)2 (M=Zr, Hf) and (Cp″)MCl3 (M=Ti, Zr, Hf, Cp″=η5-C5H5, or η5-C5(CH3)5), were immobilized on a cyclopentadienyl surface of silica with a help of n-BuLi. Before this, the silica was modified with silane coupling agent, (EtO)3Si(CH2)3Cp, by applying saturating gas–solid reactions using atomic layer chemical vapor deposition (ALCVD) technique. The heterogeneous catalysts were characterized by FTIR, 13 C and 29 Si solid state NMR spectroscopies and elemental analyses. The prepared catalysts were tested in the polymerization of ethylene using methylaluminoxane (MAO) cocatalyst. Heterogeneous catalysts CpZrCl3/S and CpHfCl3/S (S=(EtO)3Si(CH2)3Cp modified silica carrier) exhibited high activities and produced polyethylene with a narrow molar mass distribution. However, the corresponding titanium catalyst, CpTiCl3/S, exhibited low activity in ethylene polymerization and it dimerized and oligomerized ethylene. The activities of heterogeneous MCl4(THF)2/S (M=Zr, Hf) and [η5-C5(CH3)5]MCl3/S (M=Ti, Zr, Hf) catalysts were low and they all, except HfCl4(THF)2/S catalyst, produced polyethylene with a broad molar mass distribution. Catalyst leaching from the carrier was studied by treating the heterogeneous CpZrCl3/S catalyst with MAO.

Modification of zsm-5 zeolite with trimethyl phosphite part 1. structure and acidity

In the present work we have studied the structure and the acidic properties of HZSM-5 zeolite modified with trimethyl phosphite. The modifications were carried out by using a chemical vapour deposition method as well as impregnation from n-octane solution. Both modification techniques resulted in materials with similar acidic properties. Trimethyl phosphite reacted with both Bronsted acid sites and terminal SiOH groups. The modifications resulted in the total elimination of strong Bronsted acid sites accompanied by the formation of new Bronsted type sites with decreased acid strength. However, the total acidity of the modified zeolites stayed relatively high. A possible structural transformation resulting from the phosphite modifications was proposed to be an insertion of phosphorus species between the structural aluminium- and silicon-oxygen tetrahedra. However, on the basis of 31P MAS NMR studies no evidence of the isomorphous substitution of structural T-atoms by phosphorus was found.

Hydroformylation of olefins catalysed by rhodium and cobalt clusters supported on organic (Dowex) resins

Co2Rh2(CO)12 or a mixture of Co4(CO)12 and Rh4(CO)12 were impregnated onto organic Dowex® resins to study the hydroformylation of olefins. Pressure, reaction time and amount of catalyst effect the alcohol production and the ratio of straight chain to branched alcohols in the Co2Rh2(CO)12—Dowex amine resin catalytic system. 50 bar of synthesis gas pressure, 17 h total reaction time and 0.050 g catalyst were the optimum conditions in the hydroformylation of 1-hexene at 100 °C, where the maximum yield of alcohols is 95%. Other hexene isomers and different olefins were studied as hydroformylation substrates. The presence of amine groups on the support or the addition of Et3N to the hydroformylation solution is necessary for the single-step alcohol formation. This conclusion was deduced from studies of the supports with a similar matrix but different functional groups. The mixture of Co4(CO)12 and Rh4(CO)12 supported on organic amine Dowex resin is an excellent catalyst, giving 99% alcohol production. The ratio of Rh/Co has a marked effect on the product distribution. The best alcohol conversions are reached with 2.6 or 3.6 of Rh/Co weight ratio. Co2Rh2(CO)12 decomposes to give a known, but not optimum, composition of Co and Rh on the support. Therefore a mixture of Co4(CO)12 and Rh4(CO)12 is a better catalyst precursor than Co2Rh2(CO)12.