Oscar Chiantore

Drying and oxidative degradation of linseed oil

Abstract The drying and oxidative degradation of linseed oil have been investigated through exposition of samples in form of thin films to indoor laboratory conditions, or treated at a constant temperature of 80°C, or with irradiation at wavelengths >295 mm. Structure and property changes resulted almost independent of the different treatments and were followed by Fourier transform infrared analysis (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), insoluble determination and size exclusion chromatography (SEC). The initial phase of drying consists of the autoxidation phenomenon of the unsaturated fatty acid components with the development of extensive cross-linking, together with formation of conjugated unsaturations. The following stage of slow consumption of labile cross-links gives rise to a highly stable network, which contains small amounts of low molecular weight molecules, either formed by fragmentation or still present as unreacted triglycerides. The oxidative degradation of linseed oil consists of the continuation of the hardening process, and only for long periods of artificial ageing, corresponding to years of natural ageing, the oxidation also takes place on the alkylic segments, leading to partial fragmentation of the structure.

Photo-oxidative stability of paraloid acrylic protective polymers

Abstract The photo-oxidative stability of a series of commercial acrylic/methacrylic protective resins, which find use in consolidation and protection of art works, monuments and historical buildings, and are known by the name of Paraloids, has been investigated. The structural and molecular changes occurring under conditions of artificial solar light irradiation have been followed by FTIR and UV–Vis spectroscopy, and size exclusion chromatography. In all the resins the first degradative event which is detected is the molecular weight distribution change due to chain scissions and/or coupling of macroradicals. The overall stability of the polymers is strongly influenced by the presence of long alkyl side groups, such as butyl or isobutyl, whose oxidation is favoured by the presence of relatively labile hydrogen atoms. At the same time these polymers containing long ester groups undergo fast and extensive cross-linking together with some fragmentation and consequent weight losses. The resins containing only ethyl and methyl esters showed a good stability towards oxidation, reaching an equilibrium between scission reactions and macromolecular coupling which permit them to maintain their molecular characteristics during the ageing.

Photooxidative degradation of acrylic and methacrylic polymers

Abstract The photooxidative stability of poly(methyl acrylate), poly(ethyl acrylate), poly(ethyl methacrylate) and poly(butyl methacrylate) has been investigated under conditions of artificial solar light irradiation. Molecular and chemical changes induced by the light treatment were followed by size exclusion chromatography and Fourier transform infrared spectroscopy. The acrylate units were found to be more reactive towards oxidation, in comparison with the methacrylate ones. With short alkyl side groups chain scissions prevailed over cross-linking reactions both in acrylate and methacrylate samples. The degradation of poly(butyl methacrylate) proceeds in a completely different way, with extensive cross-linking and simultaneous fragmentation reactions. In all the samples the structure formed as result of oxidation reactions were similar. It has also been found that the first effect of degradation to be detected is that connected with the changes of samples molecular weight distributions.

Tailoring New Fluorinated Acrylic Copolymers as Protective Coatings for Marble

Abstract The protective performances of two new fluorinated acrylic copolymers (based on the monomers 1H,1H,2H,2H-perfluorodecyl methacrylate (XFDM) and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate (HFIM) are evaluated and compared with Paraloid B72, a commercial copolymer ethyl methacrylate/methyl acrylate (EM/MA) and its partially fluorinated homologous 2,2,2-trifluoroethyl methacrylate/MA (TFEM/MA). The polymeric materials have been tested on Candoglia marble, a very low open porosity stone (

Ageing behaviour and pyrolytic characterisation of diterpenic resins used as art materials: colophony and Venice turpentine☆

Abstract The ageing behaviour of two diterpenic resins traditionally used as artists’ materials, colophony and Venice turpentine, was investigated with different spectroscopic and chromatographic techniques. In particular, three types of ageing (natural, artificial external conditions with a xenon lamp, artificial indoor conditions with fluorescent tubes) were applied to laboratory samples to study their effects on chemical structures. Thermally-assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC/MS) was employed for careful characterisation and for identification of markers compounds on the vergin resins and in the course of ageing. The most significant changes were detected in the initial part of ageing, and the principal degradation products coming from oxidation, polymerisation and cleavage reactions identified. The high intensity of xenon lamp irradiation was found to cause, apart from oxidation and polymerisation reactions, further degradation of the chemical structure with molecular fragmentation. From the analytical point of view, the differentiation between colophony and Venice turpentine with THM-GC/MS appears to depend on differences in the lower molecular weight resin components.

Thermal-ageing of paraloid acrylic protective polymers

Abstract The thermal-ageing of a series of commercial acrylic/methacrylic resins, homo- and copolymers which are extensively used as stone protectives, has been investigated under conditions of constant temperatures at 110, 135 and 150°C. Structural and molecular changes induced by the isothermal treatments in a forced-air circulation oven were followed by infrared and UV–Vis spectroscopy, and size exclusion chromatography (SEC), respectively. The stability of the resins appeared to be controlled by the reactivity of alkyl side groups, whose oxidative decomposition is favoured in the case of long ester groups, like the isobutyl and butyl ones. At the same time, the polymers containing long ester groups undergo fast and extensive cross-linking, together with loss of short chain fragments. In the acrylic/methacrylic resins where all or the majority of the alkyl side groups are short, chain scissions prevail over cross-linking and no insoluble fractions were formed.

Ageing behaviour and analytical pyrolysis characterisation of diterpenic resins used as art materials: Manila copal and sandarac

Abstract Artificial indoor and outdoor exposure conditions have been applied in order to investigate the photo-ageing behaviour of two natural resins once used as art materials. Copals and sandarac consist of free labdane diterpenoids and of a highly cross-linked fraction of polycommunic acid. To determine the nature and the composition of the cross-linked fraction, pyrolysis is required. Thermally assisted hydrolysis and methylation, coupled with gas chromatography–mass spectrometry (THM-GC/MS), has been used to identify the acidic compounds. Many secondary pyrolysis products have been recognised and distinguished from the original resin components. Further details on the composition and ageing behaviour of Manila copal and sandarac have been obtained from Fourier transform infrared spectroscopy (FTIR), size exclusion chromatography (SEC) and direct temperature-resolved mass spectrometry (DTMS). During ageing, cross-linking and cleavage reactions were found to affect largely the chemical structure of the two resins, together with minor degradation processes such as isomerisation, defunctionalisation and oxidation.

Changes in degree of polymerization in the thermal degradation of polystyrene

Abstract The chain scission and volatilization processes which occur in the thermal degradation of polystyrene have been simulated by Monte Carlo procedures and the results have been compared with the degrees of polymerization, determined experimentally, of polystyrene samples degraded to different extents. The results of the calculations agree with random scission of the polymer chains at temperatures at which volatilization of simple molecules does not occur and with a degradation mechanism involving extensive deactivation of radicals through hydrogen abstraction from the body of polymer chains at temperatures at which volatilization does occur. The calculations also show that the molecularity index, i.e. the ratio between the weight average and the number average degrees of polymerization, tends to 2, independently of the degradation mechanism.

Photochemical stability of partially fluorinated acrylic protective coatings. I. Poly(2,2,2-trifluoroethyl methacrylate) and poly(1H, 1H, 2H, 2H-perfluorodecyl methacrylate-co-2-ethylhexyl methacrylate)s

Abstract The photochemical stability and photodegradation pathways of poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) and copolymers of 1H,1H,2H,2H-perfluorodecyl methacrylate with 2-ethylhexyl methacrylate (XFDMA–EHMA) have been investigated under artificial solar light irradiation. The extent of degradation was assessed by weight loss and gel content determination, size exclusion chromatography and FTIR spectroscopy. PTFEMA exposed up to 2000 h showed only molecular changes due to a low extent of chain scission. The two XFDMA–EHMA copolymers underwent much more degradation, with extensive cross-linking, formation of low-molecular weight products, and oxidation reactions on the chains. The behaviour of the copolymers is controlled by the reactivity of the EHMA units, as was shown by comparison with results obtained on degradation of PEHMA homopolymer.

‘Weak links’ in polystyrene

Abstract A first step in the thermal degradation of polystyrene prepared by radical polymerisation has been isolated by heating the polymer in the temperature range 199–280°C. In this step a chain scission process occurs without formation of volatile products, involving, on average, about one bond between structural units in every 10 000. This gives more direct evidence than hitherto of the presence of ‘weak links’ in polystyrene which are shown to be randomly distributed in the polymer chains, their scission resulting in a single break in the molecule of polystyrene to which they belong. The very low energy of activation for chain scission suggests that more than one rate determining step is involved in the process.