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Dear colleagues, we are extremely honoured to present to you the Proceedings of the international conference 19th Ružička Days, which was successfully held on September 21–23, 2022, in Vukovar, Croatia, in the hometown town of our famous Croatian scientist and first Nobel laureate, professor Leopold (Lavoslav) Ružička. The main goals of the Conference were to promote excellence, originality and innovation of interdisciplinary scientific research as well as the practical application of the obtained results through collaboration with industry, emphasizing thus the recognizable slogan of the Ružička Days conference: "Today Science – Tomorrow Industry". In addition, the Conference gave the opportunity for meetings, exchanging the ideas, opinions, experiences and cooperation among participants from different working surroundings. It is also important to point out that since 2008, within the international conference Ružička Days, Meeting of Young Chemists has also been held, where high school students, with the help of their mentors, present papers in the field of chemistry, with the aim to direct students and young people to the technical and natural sciences, especially chemistry. In its seventh issue (2011, 2013, 2015, 2017, 2019, 2021) the Proceedings publishes scientific and professional full papers of high quality in the following sections: Chemical analysis and synthesis (10), Chemical and biochemical engineering (3), Food technology and biotechnology (4), Chemistry in agriculture and forestry (1), Environmental protection (9) and 8th Meeting of Young Chemists (3). Full-length papers were subjected to an international review procedure done by eminent experts from the corresponding fields, to whom we express our gratitude, but they were not subjected to linguistic proofreading. On behalf of the Scientific and Organizing Committee of the 19th Ružička Days we cordially thank all the authors, reviewers, participants, lecturers, organizers, especially the international organizers EuCheMS and EHEDG, auspices and sponsors, and all the others who, in any way, supported the Conference and contributed to the preparation of the Proceedings, especially to our highly skilled and committed associates, who have put a lot of effort in the preparation of these Proceedings. At the very end, special thanks to our young, future scientists and their mentors who are faithful participants of the Meeting of Young Chemists of the Ružička Days conference. Enjoy the extremely interesting scientific and professional papers contained in these Proceedings, until the next 20th jubilee of Ružička Days in 2024! We are looking forward to meeting you again in Vukovar! Yours sincerely, Chief Editors Jurislav Babić Vesna Ocelić Bulatović Dajana Kučić Grgić

Nowadays, the paper industry is facing challenges in providing its main raw material – wood. Deforestation and the lack of reliable sources, as one concern, and transport issues as another, contribute to the rising research into new materials that can be used to partly replace wood as the main source of cellulose fibres needed for paper production. The latest research indicates that cereal straw has great potential as an additional source of cellulose fibres, due to its renewable nature and low cost. Paper substrates with added cereal straw pulp are mainly used for the secondary packaging purposes, and therefore they must show high mechanical resistance. Secondary packaging, almost always, contains printed information about the product that is exposed to various external conditions, and it is important that the print remains unchanged during transport and handling of the packaging. This research focuses on comparison of the mechanical resistance (or rub stability) of prints on papers to which straw pulp of three cereals abundant in Croatia have been added: wheat, barley, and triticale. Prints were made using UV curable inks and four different printing techniques (offset, gravure, flexographic, and digital printing). Mechanical resistance was determined by conducting the rub resistance tests and calculating the Euclidean colour difference based on measured colorimetric values of the prints before and after the tests. A comparison of the results was made to establish the best suited combination of printing technique and paper substrate containing cereal straw pulp that ensures the highest mechanical resistance of the print.

Packaging is the material with which the product is wrapped or inside which the product is placed. The main function of packaging is to protect the packaged product, identify it and place it on the market, and to ensure the original shape of the packaged goods. The trend today is to reduce the global amount of packaging waste by recycling the same waste or reusing other available waste materials, while maintaining the required quality of the packaging thus produced. Cereal grains which include wheat, rye, barley, oats, rice, corn, millet, sorghum, wheat, spelt and others, are staple foods for human and animal consumption. Each year, large quantities of stalks are left in the fields after harvesting, and after drying in the sun is mostly treated as waste. Given the high availability of cereals worldwide, cereal straw could be more usefully utilized as an alternative source of fiber for secondary packaging. Therefore, the printing paper substrates were formed from the straw pulp of three different cereal species (wheat, barley and triticale) and mixed with recycled wood pulp in a 3:7 ratio. Since offset and gravure printing are used globally to print absorbent packaging, in this study we analyzed the black prints made by these two printing techniques. The usability of the printed papers with straw pulp for secondary packaging was observed based on the penetration of the ink into the printing substrate. It was found that the composition of the paper substrate has no effect on the depth of ink penetration into the printing substrate, so that cereal straw can be used as waste material for the production of secondary packaging. In general, prints with gravure inks have lower ink penetration compared to offset inks.

The overall quality of the graphic product depends largely on the origin of the raw materials for pulp and paper, the type of ink, the technology used to print the product, and the printing conditions. Each printing technology is more or less suitable for a particular type of printing substrate, depending on how the ink is transferred to the substrate. Although the Chinese used other raw materials for papermaking almost 2, 000 years ago, wood is now the most important raw material for the production of pulp and paper. As forest areas become smaller and fewer trees are available as raw material for cellulose fibers, the production of paper and graphic products has focused heavily on the use of alternative, non-wood raw materials. Alternative cellulose fibers for papermaking from agro-residues are the most cost-effective and environmentally friendly solution that aims to reduce the consumption of wood raw materials by replacing them with alternative plant biomass. The objective of this study was to evaluate the printability of paper substrates for a specific graphic product where wood fibers are partially replaced by alternative fibers from cereal straw. Papers with a straw fiber content of 30% were produced under laboratory conditions and printed using digital and conventional printing techniques. The evaluation of the printability of paper substrates with agro-residues was based on the determination of the quality of ink acceptance on the previously printed ink, which is the basis for multicolor reproductions in the graphic industry.

Compared to papers derived from virgin fibres, recycled papers possess somewhat limited optical, strength and printing properties. Strength properties are usually increased by blending recycled fibres with virgin fibres in pulp for paper production, while optical and printing properties are often improved by coating after the paper is being manufactured. In this study, the usability of virgin fibres derived from straw as the agricultural residue of wheat, barley and triticale crops for paper production was evaluated based on the stability of prints on laboratory-made paper. For that purpose, in laboratory conditions, the papers with the addition of straw pulp in the pulp of recycled fibres were formed and prior to printing they were coated with TiO2-based coating. Process inks, in full-tone, were applied on coated straw-containing papers by digital printing process. Optical properties of digital prints upon accelerated ageing were evaluated based on Euclidean colour difference calculated from spectrophotometric values measured on black and magenta prints before and after 48 h and 96 h of ageing. The obtained results were compared with those provided by printing substrates made only from recycled fibres with and without TiO2-based coating. It was observed that TiO2-based coating has no influence on the stability of black digital prints, while each layer of TiO2-based coating reduces deviations in magenta colour upon ageing.

Svijet je suočen sa smanjenom količinom šumskih površina uslijed djelovanja požara i klimatskih promjena, te ilegalnih i neodrživih sječa šuma i njihovih prenamjena u druge svrhe. Drveće je još uvijek glavni izvor celuloznih vlakanaca, zbog čega je industrija papira kontinuirano usmjerena na traženje novih izvora sirovina. Svijest o održivom razvoju i ekologiji zahtijeva korištenje novih rješenja, kao što su alternativni izvori celuloznih vlakanaca za proizvodnju papira od poljoprivrednih ostataka biljaka koje su brzo obnovljive i jeftine za proizvodnju. Žitarice poput slame pšenice, ječma i pšenoraži dokazale su se sa svojim povoljnim svojstvima prikladnima za dobivanje celuloznih vlakanaca. U ovom radu proizvedene su laboratorijske papirnate podloge iz recikliranih drvnih vlakana s dodatkom alternativnih nedrvnih vlakanaca u masenom udjelu od 30% te je analizirana kvaliteta reprodukcije na istim. Načinjene papirnate podloge otisnute su tehnikom bakrotiska kao tehnikom kojom se omogućuje najkvalitetnija reprodukcija u području tiska ambalaže. Analiza kvalitete reprodukcije provedena je na temelju parametra neravnomjerne pokrivenosti konvencionalnim te UV bojama na dobivenim laboratorijskim tiskovnim podlogama s nedrvnim vlakancima. Vrijednosti neravnomjerne pokrivenosti bojom laboratorijskih tiskovnih podloga određene su analizom slika u programu ImageJ. Utvrđeno je da su sve analizirane tiskovne podloge otisnute visokokvalitetnom tehnikom bakrotiska ostvaruju visoku pokrivenost boje u rasponu od 97% do 98%.

Even though most information is digitized today, paper as a printing substrate is still essential. The quality of the paper depends on whether it has the properties required for its intended use, which will fundamentally rely on the raw materials used. Nowadays, the production of paper and board is increasingly focused on alternative non-wood raw materials. In this context, the main objective of this research is to improve the quality of prints on laboratory-made papers with supplementary barley pulp by coating the surface of the papers with titanium dioxide coating. Since laboratory-made papers were not subjected to the bleaching process and no additional surface treatments were used, TiO2-based coating proved to be one of the ways to improve the quality of the prints on such substrates. In this study, it was concluded that TiO2-based coating did not affect the colorimetric values of the black prints to the extent that it affected the colorimetric values of the magenta prints. However, density of printed inks was increased up to 14% for prints on laboratory-made papers with higher amount of barley pulp and TiO2-based coating in two layers.

The final quality of a graphic product largely depends on the source of raw materials for pulp and paper, the type of printing ink, the technology of printing the product and the conditions under which the printing was performed. Each analog printing technology is suitable for a particular type of printing substrate depending on the transfer of printing ink from the printing plate to the printing substrate. In the last few years, due to the over-exploitation of forests as a natural resource on a global scale, there is a growing tendency to replace wood as a traditional raw material for the production of paper with fibres from non-wood sources. The use of other cellulose sources for paper production is a costeffective and environmentally friendly solution that reduces the consumption of virgin wood pulp. In this paper, the rub stability was analyzed on a printing substrate with non - wood fibers obtained from triticale straw printed with gravure and offset UV inks. By comparing the mechanical stability of prints made by these two analog technologies, direct and indirect, the usability of innovative printing substrates with non-wood fibers was assessed.

U skladu sa sintagmom „održivi razvoj” istraživanja u ovom doktorskom radu usmjerena su na dobivanje najznačajnijih kvalitativnih parametara novoga grafičkog proizvoda, izrađenog korištenjem obnovljivih resursa koji odgovaraju standardu grafičkih proizvoda otisnutih fleksografskom tehnikom tiska. Kvalitativna ispitivanja su provedena na fleksografskim otiscima dobivenim s konvencionalnim bojama na bazi vode i modernim bojama koje se suše UV zračenjem. Otisci su tiskani na laboratorijski izrađenim papirnim podlogama koje u različitim omjerima sadrže celuloznu pulpu slame triju vrsta žitarica: pšenice, ječma, pšenoraži te recikliranog papira. Istraživanje je podijeljeno na nekoliko faza: kvalitativnu evaluaciju otiska, optičku stabilnost reprodukcije nakon standardnih metoda ispitivanja pri povišenoj temperaturi i UV svjetlosti, te djelovanje pritiska i različitih kemijskih agensa. Cilj ovog rada je definirati uporabljivost otisaka dobivenih fleksografskom tehnikom tiska na papirnim tiskovnim podlogama s alternativnim nedrvnim vlakancima. Na temelju provedenih istraživanja može se zaključiti kako laboratorijski proizvedeni papiri s dodatkom pulpe slame svih žitarica postižu zadovoljavajuću kvalitetu reprodukcije, pri čemu laboratorijski papiri otisnuti konvencionalnim bojama na bazi vode uglavnom pokazuju izvrsnu optičku stabilnost nakon izlaganja povišenoj temperaturi, kemijskim agensima i pritisku, dok laboratorijski papiri otisnuti UV sušećim fleksografskim bojama najveću otpornost pokazuju prema djelovanju pritiska. Preporuka je da se papiri iz celulozne pulpe navedenih ekološki prihvatljivijih sirovina izrade veće gramature kako bi se postigle manje vrijednosti euklidske razlike podtona i penetracije boje u tiskovnu podlogu te da se uvedu završne faze površinske obrade papira. Također, na temelju kvalitativnih analiza može se dati preporuka da se papiri s dodatkom pulpe slame žitarica otisnuti konvencionalnim bojama na bazi vode trebaju izbjegavati samo kod ambalaže proizvoda koji sadrže alkalne proizvode ili ulja. Papiri s dodatkom pulpe slame žitarica nisu prikladni za otiskivanje primarne prehrambene ambalaže UV bojama, no zbog svoje izuzetne mehaničke otpornosti mogu se upotrebljavati za tisak raznih publikacija, sekundarne ambalaže i etiketa.

The aim of this research has been to demonstrate the use and applicability of substrates containing non-wood fibres in the printing industry, with an emphasis on flexographic printing for packaging. To obtain such substrates, laboratory papers were produced with the addition of 30% non-wood fibres (wheat, barley and triticale), in combination with recycled wood pulp. These substrates were tested for chemical and mechanical resistance after flexographic printing with conventional and ultraviolet curing inks. The results showed that all laboratory papers with the addition of 30% non-wood fibres, printed with water-based inks, had fairly good chemical and mechanical resistance, except for the prints treated with sodium hydroxide. Thus, such papers should not be used as packaging materials for alkaline products. UV-curable inks on these substrates showed low chemical resistance, thus should only be used on substrates intended for secondary packaging. The mechanical resistance of UV prints was very good, thus papers containing straw pulp could be used for various applications.

Traditional papermaking is based on the use of an aqueous suspension consisting of cellulose fibres obtained by processing wood, non-wood plants or waste paper. With growing environmental concerns regarding deforestation and CO2 production, the paper industry has been always looking for new sources of non-wood pulp that would produce papers of similar quality to those made from wood pulp. Cereal straw from wheat, barley or triticale crops that remains on fields as a residue after grain harvesting has proven to be a good substitute for virgin wood fibres needed in the production of recycled paper. In this study, the quality of printed text on recycled paper with added straw pulp is evaluated mainly based on the line and edge characteristics of the printed letters. For this purpose, three types of laboratory paper substrates were first prepared using recycled wood pulp with the addition of 30% wheat, barley, or triticale straw pulp. The same letter pattern was printed with black ink on each paper substrate at a standard size of 12 pt with two common typefaces: Arial and Times New Roman. The quality of the printed letters was assessed through the measured print quality parameters such as blurriness, raggedness, fill and contrast. The resulting measurements were compared with the results obtained on the reference and control samples made exclusively from recycled wood pulp as a substrate from laboratory and commercial production. In terms of fill and contrast values, the uniformity of lines printed on the recycled papers with added straw pulp is the same or very similar to the reference and control papers. Letters printed in Arial (sans-serif) typeface show slightly better reproduction quality than letters printed in Times New Roman (serif) typeface. The measured parameters blurriness and raggedness of all laboratory-made paper substrates (with and without straw pulp) had similar values between 0.17 mm and 0.20 mm, resulting in a very similar reproduction quality compared to the reference paper substrate.

Paper composition, from the aspect of the printing substrate, and especially its surface characteristics, are of immense importance for its printability and the achieved quality of the final graphic product. When we talk about print quality, the stability of printed papers under various influences such as time, chemical agents, transport, pressure, and others are also needed to consider them as quality prints. The ink rub resistance, as one of the most important properties of printed material during the shipping or handling processes, refers to the degree of removal of an ink layer under the action of rubbing. The quality of the printed product is determined not only by the printing substrate and the selected ink (which is defined by the printing technique) but also by their interaction. Therefore, it is particularly important to choose an adequate printing substrate to achieve a quality printing. Increased concern for the environment has led to the idea that wood fibres in the pulp and paper industry must be replaced, as much as possible, with non-wood fibres. Nowadays, more and more studies indicate that fibres of various non-wood raw material can be a good substitute for wood raw fibres in the paper industry. Wheat pulp is a by-product of crop production and it has been selected as an alternative source of fibre because it is available from the annually renewable crops and is produced abundantly in numerous regions all over the world. In laboratory paper production, the collected and purified wheat straw was first cut manually and processed by the soda pulping method. The obtained unbleached semi chemical wheat pulp was added into the pulp of recycled wood fibres in a ratio of 30% to wood fibres, and laboratory papers of approximately 42.5 g/m2 were formed by Rapid-Köthen sheet former (FRANK-PTI) according to standard EN ISO 5269- 2:2004. Laboratory paper made only from pulp of recycled wood fibres was used as a reference sample. For a better insight into the utilisation of wheat pulp in pulp and paper industry, a control sample of commercially produced newsprint paper made from the pulp of recycled wood fibres was used for comparison with laboratory-made samples. In this research, the emphasis was placed on laboratory papers made with the addition of wheat pulp and on stability of the prints after they were printed with cyan, magenta, yellow and black inks by offset printing technique. Offset is an indirect lithographic printing technology and is the main printing technique in various publications. The offset printing process depends on many chemical and physical characteristics of materials and components which are involved in the process. The full tone areas with cyan, magenta, yellow and black inks have been achieved with Suncure Starluxe UV curable ink (manufacturer Sun Chemical) by Prüfbau (Multi-purpose printability tester) which simulates offset printing. After printing and drying, the samples were subjected to a mechanical resistance test (i.e., rub resistance test) on a Hanatek T4 Rub and Abrasion Tester according to the standard BS 3110 with 20, 40 and 60 circular motions at a constant speed of one rotation per second. Evaluation of the rub resistance of the UV ink layer on papers with and without wheat pulp is based on the CIE L*a*b* colorimetric values. Colorimetric values were measured before and after performed rub resistance test. The Euclidean colour difference (ΔE00) was calculated to define the tolerance between changes in coloration, i.e., fading of the colour. As mentioned, the ink rub resistance strongly depends on the surface characteristics of printing substrate. It is important to emphasize that laboratory-made papers have not gone through the final stages of surface treatment as commercially produced papers. One of the most important surface characteristics that directly affects the rub stability is roughness of the paper. Laboratory papers have a far higher surface roughness than commercially produced ones due to the lack of surface treatment. Roughness profiles of the samples' surfaces was measured with a Mahr MarSurf PS 10 profilometer to study the correlation between surface characteristics of papers with wheat pulp and rub resistance after printing them with offset UV inks. As expected, commercial papers showed better rub resistance of all printed cyan, magenta, yellow and black offset inks compared to laboratory papers. Of all analysed offset inks on commercial paper, the black ink layer showed the lowest rub resistance (ΔE00 < 1.5), while the yellow ink layer showed the highest rub resistance (ΔE00 < 0.6). Compared to commercial papers, laboratory-made reference samples after printing with cyan, magenta and yellow ink showed lower rub resistance i.e., greater ΔE00 value, while black ink layer showed approximately the same rub resistance on both papers. Adding 30% wheat pulp into the pulp of recycled wood fibres, resulted with laboratory papers that provide lower rub resistance after printing. Observing all process inks, the cyan ink layer on papers with wheat pulp had the lowest rub stability. However, the calculated ΔE00 values of ink layers of all prints were within the tolerated range, according to the tolerance definition where ΔE00 ≤ 2 is classified as a very small noticeable difference for the standard observer. In this study, it is observed that the highest colour degradation occurs after only 20 rotations of the rubbing test, while further rubbing up to 60 rotations has a negligible impact on the colour degradation of the offset UV ink layers. This research contributes to the necessary knowledge about the possibility of using non-wood sources of cellulose fibres in the paper and graphic industry, given that wood sources are increasingly limited.

The fundamental raw material in the paper industry is cellulose. Cellulose fibers are traditionally obtained from wood and are used to produce a wide range of paper substrates. The recent significant increase in the consumption of wood resources is causing a global need for alternative non-wood cellulose fibers in paper production. The straw of various cereals is often used as a source of virgin cellulose fibers. Laboratory paper substrates made of recycled paper and triticale straw pulp are used in this research. This study aimed to explore the effects of artificial and natural aging processes on the optical deterioration of digitally printed laboratory substrates with variable triticale pulp content in recycled wood pulp. The goal was to assess the optical stability of UV inkjet cyan, magenta, yellow, and black prints after two aging process treatments. The optical stability was measured by observing the reflectance in the visible spectrum. The durability of UV inkjet prints and their reproduction quality play an important role in ensuring the accuracy of text and images in graphic products. The greatest optical stability after aging for a long period of time was observed for black prints on all test substrates.

Agriculture residues are one of the most abundantly available resources worldwide as millions of tons are produced globally. Wheat is a particularly cultivated species in Croatia, and after each harvest, huge amounts of straw remain in the fields. Efficient utilization of this residue to produce paper as a printing substrate offers advantages as reducing the use of primary wood fibres and thus reducing deforestation. In this research, printing substrates with wheat straw will be evaluated in terms of chemical stability of digital prints influenced by inorganic acids. For that purpose, printing substrates were formed on the Rapid Köthen device from pulp obtained by blending different proportions of wheat pulp and pulp of recycled fibres. Colour prints (C+M, M+Y, C+Y and C+M+Y) were made in full tone by digital printing technique and prints were treated with two inorganic acids under the conditions defined in the international standard ISO 2836:2004. Based on the measured spectrophotometric values of the untreated and acid-treated prints, changes in colorimetric values of L*a*b* and the Euclidean colour difference (ΔE00*) were calculated, and the colour stability of prints was assessed. Based on the obtained results it could be concluded that wheat pulp in printing substrates ensures equal or even better colour stability of prints than pulp from recycled fibres.

In terms of volume, wood is the most available natural resource of cellulose fibres on earth. Although almost 2000 years ago the Chinese used other raw materials to make paper (bast, bark, hemp, rags and rice grass), today wood is still the most important raw material for pulp and paper production. As the forest area decreases daily, there are fewer trees as raw materials for cellulose fibres, the production of paper and paper products has significantly focused on the usability of alternative non-wood raw materials. The usage of these alternative cellulose fibres for paper production is the most cost-effective and environmental solution that aims to reduce the consumption of virgin wood pulp in paper production by replacing it with alternative plant biomass. The goal of this work was to assess the quality of offset prints on a substrate where wood fibres have been partially replaced by alternative fibres from triticale straw. For that purpose, laboratory-made printing substrate containing 30% triticale pulp was printed with UV low migration offset inks used for printing labels and non-food packaging. The assessment of the print quality on such substrates was based on the rub resistance according to the standard BS 3110:1959.

Each printing ink is formulated according to a specific printing technique in order to give the print a high degree of rub resistance to maintain equal quality during transport, storage and end use. Rub resistance is a very important parameter, which depends on the printing ink, printing substrate and printing conditions. In this paper, the rub resistance of laboratory substrates with variable content of wheat pulp printed with ink jet printing technique was analyzed. The ink jet printing technique is increasingly used for small print runs due to its variability and easy print preparation. Resistance to rubbing was evaluated according to BS 3110 standard on environmentally friendly laboratory substrates printed with magenta and cyan ink. The print stability was observed based on the color change of the prints shown through the Euclidean color difference. The analysis results showed greater rub resistance of prints on laboratory substrates with a lower share of wheat pulp with respect to all the analyzed samples. All samples printed with magenta ink show a higher degree of rub resistance than the samples printed with cyan ink.

Paper recycling is becoming increasingly important as the production of packaging and various printed products grows. As alternative to wood fiber that is the most common raw material in paper production this research examines the quality of paper which is made with addition of non-wood fibers derived from wheat straw. For this purpose, laboratory paper substrates were made by blending recycled newspaper pulp and wheat straw pulp in different proportions. In this study we analyse rub resistance of laboratory paper substrates with variable content of wheat pulp printed in full tone with black and yellow inks by digital ink jet printing technique. The main objective of this research is to determine whether this kind of print has necessary durability for carrying stable illustrations. One of the main characteristics of print quality is resistance to rubbing which is very important for packaging during transport, storage and the end use. Rub resistance test was executed according to BS 3110 standard. The print durability was assessed through the Euclidean color difference and the individual CIE L*a*b* differences before and after the rub tests. The analysis showed that the increase of wheat pulp content in paper substrates has affected the increase of color difference. Greater rub resistance was observed on substrates with lower share of wheat pulp. Samples printed with yellow ink showed overall greater durability than samples printed with black ink. In further analysis we observed that for the black prints the difference in lightness (ΔL') of the CIE L*a*b* color space was most affected as the prints became lighter with the number of rubbing cycles. In samples printed with yellow ink most affected was the color difference on yellow-blue axis (Δb') meaning that the yellowness of the prints was degrading with the number of rubbing cycles.

Flexographic and digital printing are currently the fastest growing branches in the printing industry. The selection of printing substrates for these printing techniques is large, but paper substrates are the most widely used. Paper manufacturing is based mainly on the use of renewable fibers, and the dominant fiber resource for the pulp and paper industry is wood which is accounting for 90% of the world's fiber utilization. As woods consumption for paper production is still high, there are various possibilities to reduce it. One way is by reducing the proportion of wood pulp in paper by adding straw pulp of various cereals such as wheat. Wheat straw has numerous advantages and can be used in pulp form as a source of primary fibers for paper production. As paper as a multi- component material, besides fibers composed of cellulose, hemicellulose and lignin also includes additives, minerals and synthetic polymers. Due to its complex nature it is prone to deterioration when exposed to elevated temperature, humidity and light. Paper ageing is irreversible change and is the best indicator of paper optical permanence. Objective of this study was to determine the optical stability of prints after undergoing aging treatment with elevated temperature and UV light for 48 and 96 hours. Laboratory papers containing wheat pulp were printed by two printing techniques with cyan and yellow inks to compare better optical stability: UV inkjet and flexographic technique. The optical stability of all prints was observed based on the difference in the reflection spectra (ΔR). The results indicated that all laboratory papers printed with cyan ink with flexographic technique show better optical stability than the ones printed with digital technique. Laboratory papers printed with yellow ink by both techniques show good optical stability.

Paper substrate, as the most common used substrate for printing labels or packaging, is traditionally produced from cellulose fibres derived from wood. The growth of a large number of industries has led to a significant increase in the use of such resource, which consequently led to a global awareness of the possibility of forest exploitation and the importance of reusing waste paper as a source of fibres. Hence, paper fibres can be recycled up to seven times and it is important to enrich paper pulp with virgin fibres during paper production. In such a way, the characteristics of the paper and the quality of the printed elements are improved. In this paper, cereal straw as an alternative resource of virgin fibres was turned into pulp and mixed with recycled wood pulp to conduct printing substrates using laboratory equipment. Since aging is an inevitable process of any printing substrates and prints, and the degradation of print quality due to aging largely depends on the properties of the printing substrate, ink and type of printing. This research was focused on analyzing optical stability of prints made on printing substrates with straw pulp by UV inkjet technique after natural and artificial aging. From a comparison of the aging processes based on the Euclidean difference results, it was observed that natural aging of UV inkjet prints yields less colour changes compared to artificial aging. Greater or equal optical stability after aging was perceived for prints on printing substrates with wheat, barley and triticale pulp compared to prints on substrates made with recycled wood pulp.

The bonding potential of pulp fibers is reduced by the paper recycling process. The most common technique for recovering this lost potential of secondary fibers involves upgrading the recycled pulp by blending it with virgin softwood pulps. In this research, we asses print stability on acid agents of UV inkjet prints when using straw pulp as reinforcing fibers in recycled papers. For that purpose, printing substrates were formed on the Rapid Köthen device from pulp obtained by blending different proportions of straw pulp and pulp of recycled fibers. Each printing substrate was printed in full tone with cyan, magenta, yellow, and black inks by digital technique of UV inkjet printing. Printed substrates were treated with various inorganic and organic acids under the conditions defined in the international standard ISO 2836:2004. Based on the measured spectrophotometric values of the untreated and acid-treated prints, the Euclidean color difference (ΔE00*) was defined and the stability of prints was assessed. The results of spectrophotometric measurements indicate small to medium color differences of the prints due to the effect of all acids (ΔE00max. * < 2.4) and it can be concluded that straw pulp in printing substrates from recycled fibers contributes to good chemical stability of prints. This research concludes that straw, as an annual renewable resource, can be used in conjunction with waste paper as an alternative to wood, which is currently the dominant raw material for graphic industry and producing paper.

Paper as cellulose based substrate is highly susceptible to photolytic damage caused by excessive exposure to light and temperature. Hence the focus of this research was to assess whether the wheat pulp used as a raw material for laboratory paper production can provide same or even better optical stability than papers from recycled wood pulp. For a better insight into the stability of the paper as printing substrate, study was expanded on prints made by digital technique on papers with different content of wheat pulp. Unprinted and printed papers were artificial aged using a xenon lamp with a daylight filter during 48 and 96 hours. Optical stability degradation of unprinted and printed papers was observed through Reflectance spectra (R) and by Euclidean colour difference (ΔE00). The results in this study indicated that addition of wheat pulp provide better optical stability of printed and unprinted laboratory papers.

Ofsetni tisak je tehnika tiska koja je još uvijek vodeća tehnika kod tiska papirnatih i kartonskih podloga, iako digitalni tisak također pokriva dosta veliko područje. UV ofsetni tisak u odnosu na konvencionalni ofsetni tisak razlikuje se, između ostalog, po drugačijem procesu sušenja. Ovom tehnologijom otisci se suše djelovanjem UV energije preko polimerizacije radikala. Cilj ovog rada je usporediti optičku stabilnost pri ubrzanom starenju uzoraka otisnutih s UV ofsetnom bojom i konvencionalnom ofsetnom bojom. Otiskivanje u ovom radu provodit će se na tri različite tiskovne podloge. Uzorci će biti otisnuti s UV bojom i konvencionalnom ofsetnom bojom u realnoj proizvodnji. Simulacija ubrzanog starenja na uzorcima izvesti će se na dva načina: s povišenom temperaturom (T = 60°C, u periodu od 24, 72 i 96 sati) i s Xenon lampom (T = 60°C, t = 24 sata). Na uzorcima će doći do određenog pada kvalitete otisaka koja može, a i ne mora biti vidljiva ljudskom oku. Cilj rada je definirati promjene u kvaliteti otisaka i zaključiti razliku između otisaka otisnutih UV i konvencionalnim bojama i u kojem je slučaju potrebna dodatna zaštita otiska kako bi se smanjila moguća promjena u obojenju djelovanjem dužeg stajanja u navedenim uvjetima.

Awareness of environmental issues has led to the increase in use of recycled printing papers or to the introduction of new alternative sources of cellulose fibres instead of virgin wood fibres. As recovered wood fibres cannot provide the same quality level of paper products as virgin ones, alternative sources of virgin cellulose fibres need to be identified. Therefore, the laboratory printing papers were produced using a wheat pulp in varying weight proportions and mixing with pulp from recycled paper. The print quality depends on the characteristics of the printing substrate, wherein the ink penetration is one of the important parameter. This study investigated ink penetration into laboratory papers made of different contents of pulp and their correlation with prints quality. The solid areas were printed on laboratory printing papers with cyan, yellow and magenta UV ink jet inks under standardized printing conditions. At last, the ink penetration inside laboratory papers were analyzed based on two methods (microscopic and spectroscopic) and their effect on rub resistance and print quality was also observed. Analyzed print quality parameters (ink optical density, mottling, colorimetric values) indicated that wheat pulp in the laboratory papers provides equal print quality compared to laboratory papers made from recycled pulp. The highest degradation of print quality was observed on laboratory papers with 30% of wheat pulp printed with cyan ink, as a result of the greatest measured average ink penetration depth.

Increased worldwide environmental awareness has led to a substantial increase in the use of recycled papers and new alternative sources of cellulose fibres to manufacture new paper. As recovered wood fibres do not provide the same level of paper quality as the virgin ones, alternative sources of cellulose fibers are continuously sought and researched. In this paper, the penetration profiles of UV inkjet inks within laboratory substrates formed with the addition of barley pulp in different weight proportions into pulp from recycled paper were observed. All the results have been compared to the control sample, respectively laboratory substrate produced only from recycled paper pulp. Penetration profiles were performed by observing and analyzing the microscopic images captured in the region of interest from a cross section of a pre-molded specimen into an epoxy resin. The aim of this paper is to examine whether the proportion of non-wood fibres effects the print quality, and to propose which fiber ratio is the most acceptable for paper production.

Etiketiranje stezljivim filmom je prekrivanje cijele primarne ambalaže s etiketom. Djelovanjem temperature film polimernog materijala se priljubljuje uz ambalažu i poprima njezin oblik. Ovakvo etiketiranje moguće je na različitim proizvodima i ambalažama. Promjenom dimenzije etikete mijenja se i kvaliteta otiska. Cilj ovog rada je istražiti u kojoj mjeri dolazi do degradacije kvalitete otiska pri etiketiranja stezljivim filmom. Kako bi to ustanovili uzorci su stavljeni u sušionik na temperaturu pri kojoj dolazi do skupljanja polimernog materijala. U ovom radu analizirani su fleksografski otisci na polipropilenu i poli(vinil-klorid) materijalu načinjeni s UV bojom i bojom na bazi otapala.

Cilj ovog završnog rada bio je analizirati stabilnost otiska otisnutog zlatnom tiskarskom bojom pri ubrzanom starenju. Parametri na osnovu kojih će se promatrati stabilnost otiska je kolorimetrijska vrijednost uzorka, te neravnomjerna reprodukcija tiskarske boje na tiskovnoj podlozi. Uzorci su otisnuti na laboratorijskom uređaju za simulaciju ofsetnog tiska s tiskarskim bojama koje su prilagođene za prehrambenu i duhansku ambalažu. Uzorci su otisnuti sa zlatnom tiskarskom bojom. Otiskivanje je rađeno na tri različite vrste tiskovnih podloga koje se koriste u ofsetnom tisku. Nakon otiskivanja, izvedena je simulacija starenja, odnosno ubrzano starenje otisaka djelovanjem povišene temperature u periodu od 24, 48 i 72 sata. S obzirom na djelovanje povišene temperature, pretpostavka je bila da će na uzorcima doći do određenog pada kvalitete otiska.

Kod tiska prehrambene ambalaže važno je odabrati materijale koji neće imati štetan učinak na upakirani proizvod, ali i materijale koji će biti kemijski otporni na tekućine i kemikalije koje mogu biti u sastavu takvog proizvoda. U ovom istraživanju provedena je analiza kemijske stabilnosti laboratorijskih otisaka otisnutih s inovativnom niskomigrirajućom tiskarskom bojom. Otiskivanje je rađeno na tri različite tiskovne podloge: premazanom papiru, premazanom kartonu i recikliranom papiru. Kemijska stabilnosti otisaka promatrana je nakon otiskivanja te nakon dva tretmana ubrzanog starenja otisaka (pomoću ksenonskog svjetla i pomoću povišene temperature). Ubrzano starenje otisaka izvedeno je kako bi se simulirali uvjeti duljeg stajanja prehrambene ambalaže u trgovinama. Supstance koje su korištene za analizu stabilnosti otisaka su voda, ulje, alkohol i lužina.