Tuesday, 29 December 2009
Tuesday, 22 December 2009
Cellulosic fibres exhibit a number of properties which fulfill the requirements of papermaking. These properties are: High tensile strength, suppleness (flexibility), resistance to plastic deformation, water insoluble, hydrophilic, have a wide range of dimensions, inherent bonding ability, ability to absorb modifying additives, chemically stable and relatively colourless.
Deinking chemicals are used for the removal of ink when recycling paper.
The deinking chemical agents are based on formulations of:
- Sodium hydroxide
- Sodium hydrosulfite
- Hydrogen peroxide
- Chelating agents
I use 1 litre of each and add them to the deinking cell in a specific order.
Deinking process can be broken down into several simple stages.
Recycled waste paper ----> screening and cleaning ----> wash deinking or flotation----> deinking post-flotation and dewatering.------> deinked pulp
Recycling technologies have been improved in recent years by advances in pulping, flotation deinking and cleaning/screening, resulting in the quality of paper made from secondary fibres approaching that of virgin paper. The process is a lot more eco-friendly than the virgin-papermaking process, using less energy and natural resources, produce less solid waste and fewer atmospheric emissions, and helps to preserve natural resources and landfill space.
However there are alternative ways of deinking paper which involves replacing harsh chemicals with enzymes. This is what I research.
Enzyme action is affected by the paper constituents in the de-inking condition. The chemically pulped fibres are more susceptible than mechanically pulped fibres. This is important because mechanical fibres have a lot of lignin left and hence they're much more resistant to the cellulases. Therefore, this technology works best in mills that are recycling stock paper such as office waste which is very high in chemical pulp content.
Office waste paper, unfortunately, is also high in laser and toner content, thus it has a very low value because you can't mix it with anything, and the technology for taking the toner particles out is not very good at the moment.Enzyme deinking is complemented by maceration, because the major role of cellulase is to release the toner particles from the surface of the fibre. One depends upon the mechanical action in the pulping process to release the toner particles, and physical separation remove the toner particles by flotation.
During the past twenty years the attempt to replacing chemicals with enzymes in deinking recycled paper including cellulase, xylanase, laccase and lipase, has been pursued. Cellulases and hemicellulases have been demonstrated to dislodge inks by peeling off fibres or fines on paper surfaces. Lipases have shown some direct action on ink particles either degrading oil carriers or breaking down pigments. Lignin-degrading enzymes, such as laccase, also hold some potential for deinking, as they may selectively remove surface lignin, and hence, facilitate ink removal. Cellulolytic enzymes have shown the most promising results for deinking of mixed office paper waste. I suppose this is to be expected since paper is actually cellulose. Oddly I personally am finding that amylase is the most effective at deinking. What is frustrating though is that after the end of my experiments/deinking sessions I am finding that there is so little enzyme activity left making it difficult to assay. Isn’t that typical of science?
Enzymatic versus chemical deinking has been widely examined for MOW (mixed office waste) and photocopy prints. This being the most difficult paper to deink. The use of enzymes could be an attractive alternative to chemicals in deinking. The application of enzymes in deinking has been studied on laboratory and pilot plant scale. This work has resulted in numerous patents. However, so far enzymatic deinking is rarely applied in commercial use although some promising applications include recycling. The enzymatic treatment is a competitive alternative for MOW and photocopy paper deinking. However, the process requires the selection of an adequate enzymatic preparation for each paper grade. It is less costly than chemical deinking, and it is more efficient.
These 2 methods of deinking are constantly being compared and work with enzymes will continue due the benefits gained by using them. I will leave actually paper making to the experts though I have done and enjoyed that activity.
Saturday, 12 December 2009
Sunday, 6 December 2009
I’m guessing that not many people in the blogosphere will know much about the art and science of papermaking so here is a quick guide. Just what exactly is paper? I will tell it from the point of view of a chemist ;D
It is composed of carbon, hydrogen and oxygen which of course means it is a carbohydrate. This is in the form of cellulose which itself is a long chain linear polymer of β-(1 4)-D-glucopyranose units in 4C1 conformation (i.e.glucose molecules)
Cellulose is found in plants as microfibrils, and is mostly prepared from wood pulp.
It is also produced in a highly hydrated form by some bacteria (for example, Acetobacter xylinum). So as you can now imagine, the chemistry, physics and process of papermaking is quite complex and very interesting I assure you.
Paper is such an important piece of our lives, but what do we really know about it? Papermaking began in China back in 200 BC. Chinese papermakers used old chopped-up fishing nets, tree bark, and scraps of linen and hemp to make the world's very first paper. Chinese papermaking spread slowly but steadily all over the world, from Asia into Africa and Europe. Soon just about everyone knew how to make paper. Still, there wasn't a lot of paper around, since making it gobbled up a lot of paper-making material. Early paper was made of rags, and rags were hard to come by. Ironically, when the disease called the Plague or Black Death killed millions of people in Europe, tons of clothing and rags became available - at just about the time the printing press was invented. Suddenly, more books were printed, people became better educated, and these better-educated people scratched their heads, trying to figure out a substance that might provide even more paper-making material.
We still make paper using that same basic formula. We just vary the kinds of wood fiber and energy, and the techniques of bringing it all together, to get just the kinds of paper we want. There are certainly many types of paper - newspapers, school books and writing stationery; envelopes, boxes, packing and wrapping paper; paper toweling, tissue, and personal hygiene products. Not a day goes by that we don't use paper in dozens of ways. But papermaking today, creating all the kinds of paper we use in such huge quantities, is a science as well as an art. Engineers and technicians speed things up, using computers to help guide factory machines that can produce huge rolls of paper at more than 45 miles an hour. (Thanks to TAPPI). Here is a photo of our dept pre 2004 before we merged with our textile friends.
And here is a photo which graced the entrance to our building. Sadly it was taken down and I miss it :( I hope to see it pop up again somewhere. Hopefully in one of our museums. I shall keep looking............Do you think we will need as much paper in the future as we become increasingly dependent on modern technology? Hopefully people will still treasure books as they read from their kindles. Of course we will always need tissue paper. A post in the near future will be about the biology and chemistry of paper recycling which is what I do.