Mass deacidification of papers and books. IV - A study of papers treated with aminoalkylalkoxysilanes and their resistance to ageing

In libraries and archives some of the time-acidified items are so brittle that they cannot be handled without risking loss of material. Currently used deacidification processes do not impart improved mechanical properties to the paper. The use of alcoholic solutions of three different types of aminoalkylalkoxysilanes was studied for the deacidification of paper-based items. It was shown that in addition to deacidifying and improving the stability of papers by providing an alkaline buffer the treatment also significantly improved their mechanical resistance, as measured by the folding endurance and tensile breaking resistance. Essential for the appraisal of the deacidification process, the behaviour upon ageing of the materials treated was investigated. Accelerated ageing methods involving heat/humidity and nitrogen dioxide atmosphere were used separately. It was shown that the reinforcement effect of the three aminosilane compounds tested persisted throughout the ageing, and in one case the mechanical properties even improved after ageing. Two of the aminosilanes tested were studied for their impact at the macromolecular level, on the molar masses of cellulose, using size-exclusion chromatography with multiangle light scattering detection. Their effectiveness in protecting paper from acid hydrolysis occurring during ageing was found significant.     

Paper strengthening by polyaminoalkylalkoxysilane copolymer networks applied by spray or immersion: a model study

Two di-alkoxysilanes, with (AMDES, aminopropylmethyldiethoxysilane) or without (DMDES, dimethyldiethoxysilane) an amine function, and a tri-alkoxy aminosilane (APTES, aminopropyltriethoxysilane) as well as their mixtures were introduced in paper as fiber strengthening agents. The polymerization and copolymerization of these polysiloxanes in the paper were investigated. In all the cases where APTES was present, the formation of networks was established by measuring the soluble fraction amount extracted from the treated papers. A slight decrease of the opacity of the paper sheets when AMDES was part of the treatment was noted. The presence of APTES reduced this opacity loss. The study of the physicochemical properties of the treated paper (mechanical strength and alkalinity) demonstrated that, besides the required deacidification feature, the different treatments allowed an efficient strengthening of the cellulose fibers to various extents. Contact angle measurements indicated a decrease of the hydrophilic character of papers treated with the mixture APTES/AMDES and the occurrence of a hydrophobic character of the papers treated with APTES alone. These results were consistently obtained for both spray and immersion treatment processes.     

Relationship between the decrease of degree of polymerisation of cellulose and the loss of groundwood pulp paper mechanical properties during accelerated ageing

During natural ageing, paper undergoes colour changes and becomes brittle. It is mainly due to the degradation of cellulose, the main component of paper fibres. From the viewpoint of conservation/protection of paper-based information carriers, as well as of the utilisation of secondary fibres, knowledge of the impact of a decrease of the degree of polymerisation (DP) of cellulose on mechanical properties of paper becomes of key importance. In this paper, correlations between the decrease of DP of cellulose and the loss of paper folding endurance (FE) using three model samples (pure cellulose, groundwood pulp paper, and degraded groundwood pulp paper) at accelerated ageing were investigated. The existence of such correlations between DP and FE is supported by experimental results; the correlations are linear for pure cellulose and groundwood pulp paper ageing, while exponential correlation was observed in case of degraded groundwood pulp paper. The results indicate that the rate of paper degradation can be evaluated by means of the rate of glycosidic bonds breaking in cellulosic polymer chains both for cellulose and groundwood pulp paper.     

Gamma radiation for preservation of biologically damaged paper

Samples of nine different papers in use in the library, including two mould-contaminated papers, were irradiated with 14.4 kGy in a Co-60 facility. Five of the samples were subsequently subjected to an accelerated UV-ageing process. mechanical (tensile energy absorption and stretch) and optical properties were measured on control and irradiated samples, before and after ageing.

For most samples, the effect of ageing on mechanical properties turned out to be larger than that of irradiation. Irradiated and control samples were similarly affected by the accelerated ageing. Mould contaminated samples were still in acceptable conditions of use after irradiation. No discoloration effect was observed after irradiation and/or ageing.     

Artificial ageing of double base rocket propellant

The ageing of double base rocket propellants (DB rocket propellants), which is a consequence of chemical reactions and physical processes that take place over time, has significant effect on their relevant properties (e.g. chemical composition, mechanical properties, ballistic properties, etc.). The changes of relevant properties limit the safe and reliable service life of DB rocket propellants. This is the reason why numerous research efforts are devoted to finding out reliable methods to measure the changes caused by ageing, to assess the quality at a given moment of time, and to predict remaining life-time of DB rocket propellants. In this work we studied dynamic mechanical properties of DB rocket propellant artificially aged at elevated temperatures, in order to detect and quantify changes in dynamic mechanical properties caused by the ageing. Dynamic mechanical properties were studied using dynamic mechanical analyser (DMA). The results obtained have shown that the ageing causes significant changes of DMA curve’s shape and positions. These changes are quantified by following some characteristic points on DMA curves (e.g. glass transition temperatures; storage modulus, loss modulus and tanδ at characteristic temperatures, etc.). It has been found out that the most sensitive parameters to the ageing process are: storage modulus at viscoelastic and softening region, peak width and height on loss modulus curve, glass transition and softening temperature, and tanδ at viscoelastic region.     

Cotton Cellulose Ageing in Sealed Vessels. Kinetic Model of Autocatalytic Depolymerization

In this paper, we propose a new kinetic model that describes the depolymerization of pure cotton cellulose, applicable to ageing experiments in sealed vessels. By recording the pH of the salt solutions used for controlling the relative humidity inside the vessels, we demonstrate that volatile acidic species are produced during the ageing of pure cellulose. Based on the proposition that the acids produced must have an autocatalytic effect on the depolymerization of cellulose, we theoretically developed equations describing the time dependence of the percentage of the broken glycosidic bonds, the folding endurance, tensile strength, tensile energy absorption, stretch at break and the L* and b* coordinates of the CIEL*a*b* color system. The experimentally determined values of these pure cellulose paper properties were fit into the model equations by use of a computer statistical package. The very high values of the regression coefficients indicate that the model equations work quite well. The experimental data and the model equations indicate that for long ageing times (up to 150 days at 80 °C), the deterioration of the sample properties accelerates and finally brings about an abrupt breakdown of the samples. Under the light of these findings, we believe that the useful life of the historical paper stored in archives and libraries is less than predicted by the existing models, and steps for its preservation should be taken immediately. As an additional preservation measure, we propose the ventilation of the storage areas so that the volatile acidic products of paper deterioration that accelerate its ageing are removed.     

Kinetics of the production of chain-end groups and methanol from the depolymerization of cellulose during the ageing of paper/oil systems. Part 2: Thermally-upgraded insulating papers

In order to go further in demonstrating that methanol can be used as a universal cellulose degradation indicator in power transformers, the ageing study of standard wood kraft specimens in oil in the range of 60–130 °C (Gilbert et al. in Cellulose 16:327–338, 2009) has been extended to thermally-upgraded (TU) papers. The kinetic model that best tracks the ageing patterns was shown to be a function that can accelerate or decelerate the pseudo-zero kinetics by the adjustment of a free parameter. The results showed a non-negligible contribution of 1,4-β-glycosidic bond breaking in the crystalline regions suggesting that the degradation at this level is not necessary occurring through a quantum mode mechanism. The results also showed a significant error in the determination of the rate constants when obtained from isotherms of varying degree of depolymerization. In the case of TU papers, provided that there is a sufficient amount of stabilizers in the fibrous structure, not only could the self-catalyzing nature of the cellulose ageing process as well as the effect of an external supply of catalysts be lost but the chain-breaking could decrease to nearly zero for an undetermined period well before reaching the levelling-off degree of polymerization. The initial rate constants (k _1o) for the depolymerization and methanol formation of these papers were found to be very near those of standard cellulose (giving about the same activation energy), which indicates that they are obtained from the ageing patterns well before the retardant action has fully taken place. The life extension of TU papers is achieved by a reduction with time of the frequency at which the bonds are ruptured. Moreover, the production of methanol and chain-end groups showed about the same value for the frequency factor, which introduces the possibility that the rate of production of CH₃OH from chopped chains is much higher than the rate of depolymerization, so that the latter becomes the rate determining step of the overall reaction. On the other hand, the apparent yield of CH₃OH molecules per scission is seen to increase substantially with the amount of stabilizers (from ~0.4 to 0.8 and to 1.4 for a paper containing 0 to 1.15 and to 3.9% (w/w) N₂) and to a lesser extent, with the moisture in the specimens. However, these variations could either be attributed to a modification of the CH₃OH paper/oil partitioning by the stabilizers and moisture in fibrous structure. Finally, pre-aged systems (130 °C for 168 h) conditioned at 20 °C for variable lengths of time provided further evidence that O₂ is not necessarily involved in CH₃OH production.     

Mechanical unfolding revisited through a simple but realistic model

Single-molecule experiments and their application to probe the mechanical resistance and related properties of proteins provide a new dimension in our knowledge of these important and complex biological molecules. Single-molecule techniques may not have yet overridden solution experiments as a method of choice to characterize biophysical and biological properties of proteins, but have stimulated a debate and contributed considerably to bridge theory and experiment. Here we demonstrate this latter contribution by illustrating the reach of some theoretical findings using a solvable but nontrivial molecular model whose properties are analogous to those of the corresponding experimental systems. In particular, we show the relationship between the thermodynamic and the mechanical properties of a protein. The simulations presented here also illustrate how forced and spontaneous unfolding occur through different pathways and that folding and unfolding rates at equilibrium cannot in general be obtained from forced unfolding experiments or simulations. We also study the relationship between the energy surface and the mechanical resistance of a protein and show how a simple analysis of the native state can predict much of the mechanical properties of a protein.     

Mechanical Deformation Accelerates Protein Ageing

A hallmark of tissue ageing is the irreversible oxidative modification of its proteins. We show that single proteins, kept unfolded and extended by a mechanical force, undergo accelerated ageing in times scales of minutes to days. A protein forced to be continuously unfolded completely loses its ability to contract by folding, becoming a labile polymer. Ageing rates vary among different proteins, but in all cases they lose their mechanical integrity. Random oxidative modification of cryptic side chains exposed by mechanical unfolding can be slowed by the addition of antioxidants such as ascorbic acid, or accelerated by oxidants. By contrast, proteins kept in the folded state and probed over week‐long experiments show greatly reduced rates of ageing. We demonstrate a novel approach whereby protein ageing can be greatly accelerated: the constant unfolding of a protein for hours to days is equivalent to decades of exposure to free radicals under physiological conditions.     

Changes in mechanical properties of impregnated Nomex papers 410 and 910 during accelerated aging

New materials are currently being developed for applications in transformer design. With the useful life of transformers now determined by solid insulation conditions, a better understanding of aging kinetics is important in order to improve electrical system management and planning from the technical and economic points of view. This paper summarizes an investigation of the effects of impregnating aramid and cellulose/aramid papers (Nomex 410 and 910) with insulation fluids (Nynas Polaris and Luminol Tri) at thermally accelerated conditions (170 °C) on their mechanical properties.It was found that Nomex 410 (100% aramid) showed only a small change in tensile strength (~5% decrease) after accelerated aging (around 7500 h). However, its elongation capacity was significantly reduced (~45–70% decrease for dry and wet Nomex 410, respectively) by the end of the aging process, probably due to hydrolysis. In addition, the interaction between water and aramid hydrogen bonds at high temperatures produced the rupture and then, the randomly rebuilt of these bonds in meta-aramid fibres, thereby reducing its plastic deformation capacity.In the case of Nomex 910 (aramid enhanced cellulose), its mechanical properties were maintained for a longer time than those of thermally upgraded Kraft paper (TUK), as measured by the retained percentage of tensile index. However, when the tensile index was used instead of the retained percentage, TUK showed a higher tensile index value than Nomex 910 during the initial stage, while the values for both papers became similar during the second stage. It is only at the end of the aging process that Nomex 910 presented an advantage over TUK paper due to the addition of the aramid fibres.It was also found that the inception fractures in Nomex 910, as a fibrous layered composite paper, start in the weakest part of the composite, probably in the central cellulose layer. The fracture line follows the weakest path, avoiding the aramid fibres.The results presented in this paper can be used as a benchmark for improving our understanding of aging and changes in the mechanical properties of these relatively new materials used in the solid insulation of power transformers. A better understanding of the aging characteristics (thermal degradation) of aramid-based papers should help better assess the condition of the new generation of power transformer fleets.     

Effect of overlapping cellulose nanofibrils and nanoclay layers on mechanical and barrier properties of spray-coated papers

Cellulose - This work evaluates the effect of spray-coating papers using cellulose nanofibrils (CNFs) and nanoclay (NC) on the mechanical and barrier properties for application such as reinforced...     

From paper to nanopaper: evolution of mechanical and physical properties

In the present work the evolution of physical and mechanical properties of papers and nanopapers is studied. Handsheets made of eucalyptus fibres reinforced with 0, 25, 50, 75 and 100 wt% of nanofibrillated cellulose (NFC) content were fabricated using a Rapid Köthen-like equipment. The obtained papers and nanopapers were physical- and mechanically-characterized. The results showed a significant increase in density and a reduction of porosity in the samples during their transition from paper to nanopaper; besides, nanopapers were more transparent and smoother than normal papers. These physical changes where more evident with increasing amounts of NFC. Regarding mechanical properties, nanopapers with a 100 wt% content of NFC improved their strength and rigidity in 228 and 317 %, respectively, in comparison with normal papers. The evolution of strength and rigidity from paper to nanopaper was linear in relation to the amount of NFC, which means that the ultimate tensile strength was mainly dependant on nanofibril failure.     

Chromatographic behaviour of 47 metal ions on titanium(IV) arsenate papers

Titanium arsenate papers with As/Ti ratios 0.2-2.2 have been prepared and 47 metal ions chromatographed on these papers in 10(-5)-4M nitric acid. The effect of pH and of the Ti/As ratio on the R(f) values has been studied. A new quantity R(i) (R(i) = R(f) on untreated papers minus R(f) on treated papers) has been defined. The effect of the concentration of the loading reagents on the Ti/As ratio of the ion-exchanger precipitated on the papers has been determined Contrary to Alberti, it is shown that Lederer's equation is obeyed by titanium arsenate papers in the sodium form if the activity of Na(+) ions is considered instead of their concentration. It has also been demonstrated that the selectivity sequence for cations on titanium arsenate papers is not the same as that on titanium arsenate columns.     

The ageing phenomenon of polyethersulphone hollow fibre membranes for gas separation and their characteristics

We have studied the ageing behaviour of PES/NMP (polyethersulphone/N-methyl pyrrolidone) hollow fibres for gas separation that were prepared from 35% and 37% dope. The effect of ageing on hollow fibres spun from low and high shear rate (103 vs. 862 s⁻¹) has also been investigated, in terms of their transport properties (permeation flux and separation performance), thermal, mechanical and tensile properties. Hollow fibres in this study were aged for around four months in ambient air at room temperature prior to testing.In general, the gas permeation flux drops steeply during the 40 days following fabrication and levels off thereafter. The O₂/N₂ selectivity decreases slightly over time. Hollow fibres spun with high shear rate seem to age faster than those spun with low shear rate. The gas fluxes of both membranes were found to follow a log–log relationship with ageing time. For almost all the gases used in this study, the gas flux decay rate, calculated from the slope of the log–log plot of gas flux vs. ageing, is higher for membranes spun with high shear rate. The effect of shear rate on ageing is less significant for smaller gas molecules that travel faster such as He and H₂. No significant effect of ageing on gas selectivity was observed. Experimental results also indicate that the storage modulus and loss modulus of the hollow fibres increase with ageing. Hollow fibres spun with high shear rates give a slightly higher increase in these moduli than those spun at low shear rates. Surprisingly, tangent δ (energy dissipation) and glass transitional temperature are not sensitive to ageing. We also found that the tensile yield strength and Young's modulus of the hollow fibres increase slightly with ageing. The hollow fibre membranes spun at high shear rates also show a higher increment in tensile yield stress. However, the change in Young's modulus due to ageing was similar for fibres spun with high and low shear rates.     

Ageing mechanism and mechanical degradation behaviour of polychloroprene rubber in a marine environment: Comparison of accelerated ageing and long term exposure

Polymers are widely used in marine environments due to their excellent properties and good weathering resistance. Despite this extensive use, their long term behaviour in such an aggressive environment is still not well known. To assess the polymer durability within reasonable durations, it is essential to perform accelerated ageing tests to accelerate the degradation kinetics but without any modification of the degradation process. This study therefore proposes and validates accelerated ageing tests to study marine ageing of a silica-filled chloroprene rubber (CR) used for offshore applications. Several accelerated ageing protocols are investigated for temperatures ranging from 20 to 80 °C in renewed natural seawater. The ageing consequences are characterized using physical measurements (FTIR, solid state NMR) and mechanical testing based on monotonic tension tests. Instrumented micro-indentation tests are also employed, in order to describe accurately the ageing gradients through sample thickness. The measurements obtained on the samples cut from accelerated specimens are compared to those obtained from the topcoat of an offshore flowline aged under service conditions for 23 years. For both kinds of specimens, polychloroprene develops rapid material changes most clearly represented by a considerable increase in stiffness, which allows the accelerated ageing protocols to be validated.     

Polylactide compositions. The influence of ageing on the structure, thermal and viscoelastic properties of PLA/calcium sulfate composites

High-performance composites prepared by melt-blending polylactide (PLA, l/d isomer ratio of 96/4) with various amounts of β-anhydrite II (AII), the dehydrated form of calcium sulfate hemihydrate obtained by a specific thermal treatment at 500 °C, have been aged to study the evolution of their physical and mechanical properties with time. The effect of 1-year ageing under ambient conditions (below T_g of PLA) for selected composites, i.e., filled with 20 and 40 wt% AII, was determined and compared to unfilled PLA with the same processing and ageing history. Samples with an initial amorphous PLA matrix, obtained by fast quenching from the melt, were characterized before and during ageing. The changes in physical parameters have been studied using dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and density measurements. Surprisingly, for all the samples, an increase of the storage modulus (E′) was recorded, as a result of ageing. This improvement was ascribed to the reorganization of the PLA structure induced by ageing. The structural reorganization was also reflected by a slight increase of PLA density and changes in thermal behaviour. The X-ray investigations showed unchanged crystallographic structure of AII both during blending with molten PLA and in the composite systems after ageing. The surprising stability of the thermo-mechanical properties of PLA and PLA/AII composites is in agreement with the results of size exclusion chromatography analysis (SEC) which did not show significant changes of PLA molecular weights brought out by ageing.     

Structure and properties of degradable polyolefin-starch blends

The structure, mechanical properties and susceptibility to degradation of blends of low density polyethylene (PE) or isotactic polypropylene (PP) and glycerol plasticized starch (GS) was investigated. Monoethers of glycerol and fatty alcohols (GA) and in some cases epoxidized rubbers (ER) were used as compatibilizers for the investigated systems. It was found that mechanical properties and ageing susceptibility of blends depend strongly on their composition, i.e. the content of plasticized starch in the blend and the content of glycerol in the starch. In some cases an increased susceptibility to biodegradation during soil or fungus ageing not only of the starch phase but also of the polymer phase was observed. The susceptibility of these systems to accelerated artificial weathering was also investigated.     

Application of cooling curve analysis in solidification pattern and structure control of grey cast irons

In this article, the composites based on long glass fibre reinforced polypropylene/intumescent flame retardant (LGFPP/IFR) were prepared by melt blending. The influence of thermal oxidative ageing on the LGFPP/IFR composites with different thermal oxidative ageing time at 140 °C was studied by means of oven heating. The thermal stability and flammability of the composites were respectively investigated by thermal gravimetric analysis (TG), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), scanning electronic microscopy (SEM), mechanical properties test and energy-dispersive X-ray analysis (EDAX). A trend of increase first and then decrease in LOI values was shown in 0–50 days ageing, with the same trend as thermal stability obtained from TG in nitrogen condition. The CCT results indicated that the LGFPP/IFR composites after ageing achieved a higher heat release rate, which means a higher fire risk. The mechanical properties showed a global decrease in just 10 days ageing. Morphologies obtained from SEM showed that both the rupture of PP matrix and fibre interface debonding led to the decrease in mechanical properties. The EDAX proved that IFR particles could emerge and gather on the surface of sample in ageing procedure, which had great effects on the thermal stability and flame retardancy of the composites.     

Effect of butadiene/styrene ratio,block structure and carbon nanotube content on the mechanical and electrical properties of thermoplastic elastomers after UV ageing

Thermoplastic elastomers based on a triblock copolymer styrene-butadiene-styrene (SBS) with different butadiene/styrene ratios, block structure and carbon nanotube (CNT) content were submitted to accelerated weathering in a Xenontest, in order to evaluate their stability to UV ageing. It was concluded that ageing mainly depends on butadiene/styrene ratio and block structure, with radial block structures exhibiting faster ageing than linear block structures. Moreover, the presence of carbon nanotubes in the SBS copolymer slows down the ageing of the copolymer. The evaluation of the influence of ageing on the mechanical and electrical properties demonstrates that the mechanical degradation is higher for the C401 sample, which is the SBS sample with the largest butadiene content and a radial block structure. On the other hand, a copolymer derivative from SBS, the styrene-ethylene/butadiene-styrene (SEBS) sample, retains a maximum deformation of ∼1000% after 80 h of accelerated ageing. The hydrophobicity of the samples decreases with increasing ageing time, the effect being larger for the samples with higher butadiene content. It is also verified that cytotoxicity increases with increasing UV ageing, with the exception of SEBS, which remains non-cytotoxic up to 80 h of accelerated ageing time, demonstrating its potential for applications involving exposure to the environment.