| Abstract: | CONCLUSION. Original untreated newsprint is subjected to rapid self-destruction process resulting in fall of mechanical properties, paper becomes brittle and fragile, its acidity is increased. Creation of colour degradation products, absorbing visible radiation within the range of 600 nm was indicated by 51 % increase of colour co-ordinate b*. Ageing caused a substantial colour changes of paper in general. Removal of acidic degradation products by washing in distilled water improved the original strength properties which results probably from partial revival of inter-fibre hydrogen bonds. The improvement of pH values, folding endurance, tensile strength and optical properties can be observed also after accelerated ageing in comparison with untreated newsprint. Removal of acidic products before one-sided lamination caused pH increase up to nearly neutral medium and its influence is more obvious for two-sided laminated samples despite pH reading still remained in neutral medium. Paper washed before lamination showed better results than unwashed laminated paper. Mechanical properties of washed one and two-sided laminated samples before ageing were higher than properties of unwashed samples; however ageing process brought them closer and the differences were less obvious. Paper deacidification caused changes of its mechanical and chemical properties. It positively increased pH value up to alkaline range; samples remained alkaline also after the ageing. It seems that better result provided paper washed before deacidification than unwashed deacidified paper despite this difference is not statistically significant. Deacidification caused decrease of mechanical properties before ageing in comparison with identical samples without deacidification; however the influence of deacidification treatment significantly improved mechanical properties of samples after ageing compared to untreated newsprint. Removal of acidic products by washing before deacidification yet caused partial decrease of mechanical properties after ageing in comparison to unwashed paper. Paper deacidification before one and two-sided lamination caused decrease of mechanical properties in comparison with non-deacidified paper; acidic products removal before deacidification influenced positively increase of mechanical properties. Newsprint deacidification caused its substantial colour change compared to non-deacidified paper; it became more yellow before and after ageing as well. For one an two-sided laminated samples the value of co-ordinate b* decreased - caused by the layer of lamination film - also after the ageing compared to non-laminated samples. Yellowing of deacidified one an two-sided laminated samples was lesser than for non-laminated samples. Washing of paper before lamination (WD) caused decrease of colour difference and colour coordinate b* lowering compared to ND sample. Washing and deacidification before one and two-sided lamination caused slightly more yellowing after ageing compared to unwashed and deacidified one or two-sided laminated samples. Resizing of paper by Thylose MH 300 after previous washing and deacidification significantly increased pH values and tensile strength, however after ageing this paper became very brittle and reached the highest reading of yellowing (the biggest change of b*). Subsequent one and two-sided lamination caused even more distinct shift to alkaline range also after the ageing; the samples showed improvement of their mechanical properties. One-sided laminated papers sized by Thylose (WDTL) became the most brittle and yellow among deacidified one-sided laminated papers after the ageing. Two-sided lamination (WDTLL) provided the highest tensile load values and just after WDLL samples also folding endurance. The accelerated ageing caused substantial yellowing of these samples. One-sided lamination caused 59 % increase of basis weight (two-sided 121 %) and 50 X thickness increase (94 % for two-sided lamination). Both types of lamination were more effective after deacidification when pH reading remained in slightly alkaline range. Mechanical properties after ageing were improved and the improvement was more obvious for papers previously deacidified and washed; a substantial increase showed two-sided lamination samples. Colour change for one-sided laminated samples were less obvious during ageing than for two-sided laminated samples, however non-laminated side was dissimilar to laminated side. |
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