A Study On Deinking Chemistry Of Mixed Office Wastepaper

Office wastepaper has been becoming one of the large four classes of wastepapers for ever-increasing utilization of xerographic and laser printed paper.Recycled office waste papers are potentially an excellent source of low cost, highquality fiber for the papermaking industry. The major problem in using mixed officewastepaper (MOW) is that it contains a high percentage of difficut-to-deink,non-impact printed papers, such as photocopier and laser printed papers. The inks fornon-impact printing are very different from the traditional in their compositions andcharacters. This type of ink particle is very difficult to remove from the pulp byconventional mechanical means such as washing, flotation, screening and centrifugalcleaning. Deinking of secondary fiber is a complicated chemical and physical process.Ink removal requires chemical, mechanical, and thermal energy. Each of these energyinputs interacts with the others. Surfactants play important roles in deinkingoperation, its main functions are decontamination, dispersion, wetting, emulsification,collection, foaming. Therefore, for increasing utilization rate of MOW, it is veryimportant to study deinking chemistry of MOW and the effect of surfactant structureon MOW deinking.Based on the principle of anion polymerization, a series of surfactants areprepared in this dissertation. PEP surfactants are prepared by reaction of propyleneoxide with compounds containing two reactive hydrogen atoms in the presence ofpotassium hydroxide. Using an alcohol with 8 to 18 carbon atoms per molecule as aninitiator, the alcohol is condensed with ethylene oxide, followed by propylene oxide,in the presence of potassium hydroxide and a proper temperature, to give a range ofmonoalkyl ethers of ethylene oxide/propylene oxide block copolymers. Adding POunits modifies a series of AEO and TX surfactants. Carboxymethylated alcohol ethersare prepared by the reaction of ether alcohols and chloroacetic acid with sodiumhydroxide. The molecule structures of surfactants prepared are confirmed by IRspectrum and H-NMR spectrum analyses. 1The relations of basic surface physicochemical properties and appliedperformance of surfactants with its structure are investigated. The surface tension ofPEP nonionic surfactants depends on not only PO/EO but also the respective chainlength of PO and EO. For the same in the chain length of EO, the surface tensiondecreases with the increase of PO/EO value. For the same in PO/EO value, thesurface tension decreases with the increase of the chain length of EO. For the sameinitiator,the cloud point lowers with the increase of PO content. For fatty alcoholsethylene oxide/propylene oxide block copolymer, the surface tension increases as thecarbon-chain length in the alkyl increases. As the number of PO units in moleculestructure increases, the surface tension increases while water-solubility, foaming andfoam stability decreases. The similar variation can be found in alkyl phenols EO/POblock copolymer. The more the number of PO units, the higher the surface tensionand the poor the water-solubility, foaming and foam stability. Using ERIC value of flotation accepts and flotation-deinking efficiency as theevaluation indexes of a flotation deinking process, the effects of surfactant structureon flotation deinking of MOW are studied. Both high-alcohol EO/PO blockcopolymers and alkyl ether carboxylic acids surfactants have better flotation deinkingeffects than the others in the research. The ERIC values of their flotation accept arelower and the flotation deinking efficiencies are higher. For PEP surfactants, there isan optimal value for the number of PO unit in molecule, which varied with theinitiators. As compared with AEO and TX series, modified surfactants by adding POunits can improve the effects of MOW flotation deinking. For the same number of EOunits, the flotation accepts ERIC response decreases as the number of PO unitsincreases. Generally speaking, for the same number of PO units, the flotation acceptsERIC response decreases as the number of EO units increases. Studies on agglomeration deinking of MOW are performed. It is found thatsurfactants can improve the effect of 1-Octadecanol agglomeration deinking and theinfluences of different surfactants have variations. For PEP surfactants, the deinkingeffect relates to not only PO/EO but also the respective chain length. As comparedwith AEO series, modified surfactants by adding PO units have poor deinking effects.