Suzana M. Cakić

Fast Fourier Transform IR Characterization of Epoxy GY Systems Crosslinked with Aliphatic and Cycloaliphatic EH Polyamine Adducts

The use of fast FT-IR spectroscopy as a sensitive method to estimate a change of the crosslinking kinetics of epoxy resin with polyamine adducts is described in this study. A new epoxy formulation based on the use of polyamine adducts as the hardeners was analyzed. Crosslinking reactions of the different stoichiometric mixtures of the unmodified GY250 epoxy resin with the aliphatic EH606 and the cycloaliphatic EH637 polyamine adducts were studied using mid FT-IR spectroscopic techniques. As the crosslinking proceeded, the primary amine groups in polyamine adduct are converted to secondary and the tertiary amines. The decrease in the IR band intensity of epoxy groups at about 915 cm−1, as well as at about 3,056 cm−1, was observed due to process. Mid IR spectral analysis was used to calculate the content of the epoxy groups as a function of crosslinking time and the crosslinking degree of resin. The amount of all the epoxy species was estimated from IR spectra to changes during the crosslinking kinetics of epichlorhydrin.

Synthesis and Characterisation of Polyester Based on Isosorbide and Butanedioic Acid

Copolyesters based on isosorbide and butanedioic acid in combination with monomers such as adipic acid and dimethyl terephthalate, poly(isosorbide-co-butanedioic acid) (and -co-adipic acid) and poly(isosorbide-co-butanedioic acid-co-dimethyl terephthalate), were synthesized and characterized. Linear OH-functionalized polyesters were obtained via melt polyesterification of dicarboxylic acids with OH-functional monomers. The type of end-group was controlled by the monomer stoichiometry and hydroxyl functional group is formed in time. Average molecular masses of synthesised polyesters were measured by gel permeation chromatography. The glass transition temperatures and thermal stability of the obtained polyesters were effectively adjusted by varying polymer composition and molar mass. Addition of adipic acid or dimethyl terephthalate increased glass transition temperatures of obtained polyesters. Thermal stability of obtained polyester slightly increases by the increasing of dimethyl terephthalate content. Molecular structures of obtained polyester were assessed by Fourier transform infrared spectra and 1H NMR spectroscopy.

Structural Differences Between Lignin Model Polymers Synthesized from Various Monomers

In a plant cell wall, lignin is synthesized from several monomeric precursors, combined in various ratios. The variation in monomer type and quantity enables multifunctional role of lignin in plants. Thus, it is important to know how different combinations of lignin monomers impact variability of bond types and local structural changes in the polymer. Lignin model polymers are a good model system for studies of relation between variations of the starting monomers and structural variations within the polymer. We synthesized lignin model polymers from three monomers, CF—based on coniferyl alcohol and ferulic acid in monomer proportions 5:1 and 10:1 (w/w), CP—based on coniferyl alcohol and p-coumaric acid in proportion 10:1 (w/w) and CA—based on pure coniferyl alcohol. We studied structural modifications in the obtained polymers, by combining fluorescence microscopy and spectroscopy, FT-IR and Raman spectroscopy, in parallel with determination of polymers’ molecular mass distribution. The differences in the low Mw region of the distribution curves of the 10:1 polymers in comparison with the CA polymer may be connected with the increased content of C=C bonds and decreased content of condensed structures, as observed in FT-IR spectra and indicated by the analysis of fluorescence spectra. The 5:1 CF polymer contains a different type of structure in comparison with the 10:1 CF polymers, reflected in its simpler Mw distribution, higher homogeneity of the fluorescence emitting structures and in the appearance of a new high-wavelength emission component. We propose that this component may originate from π-conjugated chains, which are longer in this polymer. The results are a contribution to the understanding of the involvement of structural variations of lignin polymers in the cell wall structural plasticity.

Synthesis and properties of novel star-shaped polyesters based on l -lactide and castor oil

The topology of biodegradable polyesters can be adjusted by incorporating multifunctional polyols into the polyester backbone to obtain branched polymers. The aim of this study was to prepare the biodegradable-branched polyester polyols based on l-lactide and castor oil using the trifluoromethanesulfonic acid as a catalyst. FTIR and 1H NMR spectroscopy measurements were used to estimate the molecular structure of the novel materials. The polyester polyol was synthesized by ‘‘core-first” method which involves a polymerization of l-lactide by using a castor oil as multifunctional initiator. Molar masses estimated by gel permeation chromatography and vapor pressure osmometry were in good correlation with calculated values based on hydroxyl number of obtained polymers. DSC measurements confirmed high crystallinity degree of the synthesized material. It was assessed that the molar masses of obtained polymers-influenced glass transition temperature significantly. The thermal stability was investigated by TG analysis, and the results have shown the dependence of weight loss on the arm length of the star-shaped polyesters. The thermal stability of star-shaped polyesters significantly decreased with degradation of polyester polyol obtained in acid solution.

The Thermal Degradation of Waterborne Polyurethanes with Catalysts of Different Selectivity

The thermal stability of waterborne polyurethanes was measured by use of the thermogravimetric analysis. Waterborne polyurethanes (wbPUR) with catalysts of different selectivity were characterized using dynamic heating. In the dynamic method, heating rates with increments of 0.5, 1, 2, 5, and 10°C min−1 were used in the range of 30–500°C, to achieve degradations of 0.025, 0.05, and 0.10, respectively. By using more selective catalysts, the resulting total time of decomposition was increased in all cases of degradation degrees for given initial temperature of waterborne polyurethanes. This paper shows how the dynamic method based on thermogravimetric analysis can be used to calculate the thermal stabilities of waterborne polyurethanes, using catalysts of different selectivity.

FTIR analysis and the effects of alkyd/melamine resin ratio on the properties of the coatings

Alkyd/melamine resin mixtures are mainly used in industrial baking enamels. The effects of the alkyd/butylated melamine resin ratio (from 90/10 to 50/50) and curing temperature (from 110 to 180°C) on the crosslinking and properties of the coating are presented in this paper. The curing reactions through functional groups of resins were monitored by FT-IR spectroscopy. The hardness, elasticity, degree of adherence and gloss were also determined. Optimal coating properties could be achieved with an alkyd/melamine resin ratio of 80/20, a curing temperature of 150°C and a curing time of 20 min.

Thermal Analysis of Polyurethane Dispersions Based on Different Polyols

Water-based polyurethane dispersions (PUD) are a rapidly growing segment of polyurethane (PU) coatings industry due to environmental legislations such as the clean air act and also due to technological advances that made them an effective substitute for the solvent-based analogs. Water-based or waterborne PUD have gained increasing importance in a range of applications, due in large part to properties such as adhesion to a range of substrates, resistance to chemicals, solvents and water, abrasion resistance and flexibility. Water-based PUD show very good mechanical and chemical properties and match the regulatory pressures for low volatile organic compound (VOC) containing raw paints. The continuous reduction in costs and the control of VOC emissions are increasing the use of water-based resins, motivating the development of PU dispersed in water. PU obtained from water-based PUD have superior properties when compared with similar materials obtained from organic media. Water-based PUD are used in many application areas to coat a wide range of substrates for example footwear adhesives, wood lacquers for flooring and furniture, leather finishings, plastic coatings, printing inks and automotive base coats (Rothause et al., 1987; Kim et al., 1994; Ramesh et al., 1994).

The influence of the nanofiller on thermal properties of thermoplastic polyurethane elastomers

Hybrid materials based on renewable resources are under huge interest of scientist nowadays. Polymer-based hybrid materials with the addition of nanoparticles are very interesting because the addition of small amount of nanoparticles significantly improves final material’s properties. Group of polymers which is suitable for use for hybrid materials preparation are polyurethanes. Polyurethanes have wide spectra of commercial and industrial applications, but for their production petroleum-based derivative is used and big efforts are still making for changing it with components from renewable resources. Thermoplastic polyurethanes were synthesized using two types of isocyanates: isophorone diisocyanate and hexamethylene diisocyanate, and the possibility of using isosorbide, instead of butanediol, as chain extender for the synthesis of thermoplastic polyurethane elastomers was investigated. NCO/OH ratio was 1.15/1 and soft segment content 50% in all samples. Also, the influence of the addition of hydrophilic and hydrophobic silicon(IV)-oxide nanoparticles, in amounts of 0.5,1, 2, and 5%, on thermal properties of the obtained green polyurethanes is determined using DSC and TG analysis. It is shown that hydrophilic silicon(IV)-oxide nanoparticles have an influence on thermal properties of soft segment in polyurethane structure, while hydrophobic ones have the influence on hard polyurethane’s segment properties, increasing Tg values. Thermal stability of polyurethanes increased with increasing the amount of nanoparticles added. FT-IR analysis showed that there is no chemical reaction between polymer and nanoparticles.

Synthesis, spectroscopic and thermal characterization of new metal-containing isocyanate-based polymers

AbstractTo overcome the polyurethanes low heat resistance and obtain new PU-based materials, in continuation of our research in the synthesis of hybrid polymers, we report here the synthesis of metal-containing polyurethanes formed in the reaction of pyrazole-based coordination compounds [Cuampf(NO3)2MeOH]·MeOH and [CuampfCl2] where ampf denotes N,N′-bis(4-acetyl-5-methyl pyrazole-3-yl)formamidine ligand, and two isocyanates, 1,6-diisocyanatohexane (HDI) and Bayhydur 3100 (Bay, a hydrophilic linear polymer based on 1,6-diisocyanatohexane) using dibutyltin-dilaurate catalyst. The formed materials were characterized by FT-IR spectrometry and thermal methods. The formation of the new polymers, besides the corresponding FT-IR spectra, was proved by differential scanning calorimetry (DSC) determining their glass transition temperatures. The thermal decomposition of the materials was examined by simultaneous thermogravimetric (TG) and DSC measurement. For the evaluation of the decomposition mechanism, the data obtained by coupled TG–mass spectrometric (MS) measurements were used. The thermal stability of the hybrid materials based on HDI was found substantially higher than that of the pure 1,6-diisocyanatohexane and decomposition of hybrid materials was more complex, while in the reaction of the metal complexes with Bay the thermal properties of the obtained hybrid polymers were changed only slightly, referring to a small amount of incorporated complexes.

The investigation reaction kinetic for polyurethanes based on different types of diisocyanate and castor oil

The formation of polyurethanes based on vegetable oils is very complex and thus for industrial production of this materials it is important to determine the optimal temperature for polymerisation and finally to obtain materials with the proper mechanical properties. The goal of this work was to assess the kinetic of catalysed and noncatalysed reactions for polyurethanes based on castor oil as the polyol component and different types of diisocyanates. Due to the presences of hydroxyl groups on ricinoleic acid, castor oil is suitable for polyurethane preparation. The differential scanning calorimetry has been employed to study the polyurethane formation reaction using Ozawa isoconversion method. It was estimated that the catalyst addition decreases the activation energy. The highest reduction of activation energy was observed for the reactive systems with hexamethylene diisocyanate. Validity of obtained kinetic model was examined by FTIR spectroscopy following the apsorption of reactive groups. Obtained results of mechanical characteristics of the polyuretahane networks (with different NCO/OH ratio) confirmed that applied method could be used for prediction of optimal reaction condition in polyurethane networks synthesis.