these would have answered the questions you posed today.
Q.what direction does the water in your sink go when it is drained?
from http://www2.abc.net.au/science/k2/stn/november1999/posts/topic8390.shtm
| From: steve(primus) | 18/11/99 13:25:08 |
| Subject: re: Water Direction | post id: 8417 |
| f water, when going down a drain, goes in an anti clockwise direction in one hemisphere and clockwise in the other hemisphere - what happens at a) the equator? b) the poles? Water goes down a drain in either hemisphere whichever way it wants to. The Coriolis effect, which is zero at the equator and strongest at the poles, is caused by the rotation of the earth which has a rotational speed of one revolution per day. Water going down a plughole is revolving faster than that so there are other forces involved. The currents in the water due to the water temperature, the shape of the bath/tank, the currents you set up by removing the plug or getting out of the bath all have an effect, and these override the very weak effect of Coriolis. water spirals down drains at the poles and on the equator just as it does anywhere else - and the direction is determined by a number of factors. However, if you had a tank large enough and the water in it still enough so there were no other influences on the spiral direction, then, yes, coriolis would come into play but for general purposes, it has no effect at all. | |
from http://www.theanswerbank.co.uk/Science/Question271805.html
http://www.youtube.com/watch?v=cpb0XLUDGag
http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html
http://www.youtube.com/watch?v=cpb0XLUDGag
http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html
also check out
http://www.guardian.co.uk/science/2003/nov/13/research.science
Q. why does paper yellow over time? Does it become more acidic or alkaline as it ages?
Lignin is the main source of color in pulp due to the presence of a variety of chromophores naturally present in the wood or created in the pulp mill.
Paper is made from wood, which is made up mainly of white cellulose. Wood also has a lot of a dark substance in it called lignin, which ends up in the paper, too, along with the cellulose. The exposure of lignin to air and sunlight is what turns paper yellow.
Lignin eventually turns paper yellow because of oxidation. That is, the lignin molecules, when exposed to oxygen in the air, begin to change and become less stable. The lignin will absorb more light, giving off a darker color.
Mechanical pulps retain most of the lignin present in the wood used to make the pulp and thus contain almost as much lignin as they do cellulose and hemicellulose. It would be impractical to remove this much lignin by bleaching, and undesirable since one of the big advantages of mechanical pulp is the high yield of pulp based on wood used. Therefore the objective of bleaching mechanical pulp (also referred to as brightening) is to remove only the chromophores (color-causing groups). This is possible because the structures responsible for color are also more susceptible to oxidation or reduction.
Alkaline hydrogen peroxide is the most commonly used bleaching agent for mechanical pulp. The amount of base such as sodium hydroxide is less than that used in bleaching chemical pulps and the temperatures are lower. These conditions allow alkaline peroxide to selectively oxidize non-aromatic conjugated groups responsible for absorbing visible light. The decomposition of hydrogen peroxide is catalyzed by transition metals, and iron, manganese and copper are of particular importance in pulp bleaching. The use of chelating agents like EDTA to remove some of these metal ions from the pulp prior to adding peroxide allows the peroxide to be used more efficiently. Magnesium salts and sodium silicate are also added to improve bleaching with alkaline peroxide[5]
Sodium dithionite (Na2S2O4), also known as sodium hydrosulfite, is the other main reagent used to brighten mechanical pulps. In contrast to hydrogen peroxide, which oxidizes the chromophores, dithionite reduces these color-causing groups. Dithionite reacts with oxygen, so efficient use of dithionite requires that oxygen exposure be minimized during its use.[2]
Chelating agents can contribute to brightness gain by sequestering iron ions, for example as EDTA complexes, which are less colored than the complexes formed between iron and lignin[2].
The brightness gains achieved in bleaching mechanical pulps are temporary since almost all of the lignin present in the wood is still present in the pulp. Exposure to air and light can produce new chromophores from this residual lignin.[6] This is why newspaper yellows as it ages.
Archival paper is lignin-free and acid-free (between pH 6.0 and 8 is considered acid-free, between pH 7.1 and 8.0 is called alkaline buffered, this delays the gradual deterioration of the sheet).
1. An alkaline pulping process for chips of lignocellulosic material which comprises cooking said lignocellulosic material at 140°-210° C. for 250 minutes with a solution containing sodium sulfite at a pH of 10-13.5 in the presence of sodium aluminate as a buffering agent in the amount of 2% to 8% as NaOH based on the dry weight of the chips of lignocellulosic material, and 0.2% anthraquinone, wherein said cooking is carried out to produce a pulp of high viscosity, high strength and good yield.
FIELD OF THE INVENTION
The present invention relates to the formation of the paper web using neutral pH forming conditions and wherein calcium carbonate is used as the principal filler.
BACKGROUND OF THE PRESENT INVENTION
It is known to manufacture paper by supplying the papermaking stock to the forming section of a paper machine under acid, neutral or alkaline conditions. Alkaline conditions are primarily used with a wood free fiber and at a pH in the range ofabout 8 whereas in acid papermaking from wood containing stock, the pH is generally well below 7 and normally in the order of 4 to 6. Neutral papermaking is usually carried out at pH of about 6.8 to 7.5.
One of the major advantages of alkaline papermaking is that it permits the use of calcium carbonate which is a relatively inexpensive filler in relatively large quantities in the paper. Calcium carbonate is generally less expensive than woodfiber and has a relatively high brightness which thus facilitates the production of low cost priming papers.
Attempts have been made to utilize calcium carbonate filler with acid papermaking and/or neutral papermaking by means of specific acid tolerant carbonates which are specially prepared, for example, by the addition of phosphorus compounds to thesurface of the carbonate to stabilize the carbonate under acid conditions. It is also known when using such acid tolerant carbonates to operate the paper machine at pH generally below 7 (i.e. mild acid conditions) and to use phosphoric acid to maintainthe pH of the stock.
Chalk has been used as a filler in paper.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
It is an object of the present invention to provide a process for making paper under neutral papermaking conditions while incorporating natural calcium carbonate filler into the furnish.
Broadly, the present invention relates to a method of making paper from a furnish containing predominantly mechanical pulp under substantially neutral conditions comprising adding natural calcium carbonate to a mechanical pulp stock being fed toa headbox of a forming section of a paper machine, adding bentonite and a suitable polymer to said stock, controllably adding a pH reducing and buffering agent to said stock being fed to said headbox to maintain the pH of said pulp stock in said headboxwithin the range of 6.7 and 7.5, forming a sheet by separating white water containing calcium carbonate from the pulp stock in said forming section, recirculating said white water containing calcium carbonate to said headbox with said pulp stock.
Preferably said polymer comprises a polyacrylamide polymer
Preferably said pH reducing and buffering agent will comprise phosphoric acid.
Preferably, the form of said natural calcium carbonate will be chalk.
Preferably, the pH of said stock in the headbox will be sensed and addition of phosphoric acid to maintain said pH in said range of 6.7 to 7.5 controlled based on said pH sensed in said headbox.
Preferably said pH range will be 6.9 to 7.4
BRIEF DESCRIPTION OF THE DRAWINGS
Further features, objects and advantages will be evident from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawing in which;
FIG. 1 is a schematic flow diagram for a paper machine incorporating the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The term calcium carbonate has been used in relation to the present to describe natural calcium carbonate as opposed to and to distinguish from precipitated calcium carbonate which has not been found to be satisfactory for practising the presentinvention.
.............
Acid-Free: Materials with a pH of 7.0 or higher are considered acid-free. Acid-free materials can be either buffered or unbuffered. Buffering agents typically raise the pH of a material to 8.0 or higher. Unbuffered materials can become acidic over time by the absorbtion of acids from the environment.
Archival (Archival Quality): This non-technical term suggests that a material is safe for long term storage and does not contain any chemicals that could adversely affect a collection. The phrase is not quantifiable or standardized, and therefore should not be considered, independently, as a guarantee of acceptable storage criteria.
Archival Polyester: Mylar D, long recognized as the premier brand of clear polyester for preservation purposes, was recently discontinued by the manufacturer. A variety of additional brands of polyester of equal quality remain available. The AstuteCollector.Com uses only the highest grades of polyester in creating it's variety of polyester enclosures.
Buffering: Paper and paperboard products are divided between buffered and unbuffered. Calcium carbonate is the preferred buffering agent of preservation professionals. The buffering agent helps neutralize acids in the environment and help to prevent those acids from attacking your collections. Because of concerns over the affect of buffering agents on certain animal bye products such as wool, leather and silk, unbuffered paper and paperboards are often preferred for storing these materials as well as certain rare photographic collections. Note: Unbuffered materials can absorb acids from the environment and can, eventually become acidic themselves.
Calcium Carbonate: The preferred buffering agent of preservation professionals, Calcium Carbonate is added to paper pulp during the paper making process in order to neutralize acids. It's prescence in folders, boxes, and other enclosures helps ensure that acids in the environment are neutralized.
Lignin (Lignin-Free): Lignin is a naturally occuring substance found in plants and wood pulp. Lignin is thought to contribute to the early degradation of paper and is often removed during the pulping process to create higher grade paper.
PAT (Photo Activity Test): The PAT is an accelerated aging test that predicts the interaction between enclosures and photographic images and can be used to determine possible photographic activity caused by components of those enclosures including adhesives, inks, etc.
Polyvinyl Chloride (PVC): This is a plastic that can emit damaging hydrochloric acids as it degrades, causing damage to materials stored within. PVC often emits a strong odor such as that given off by a new plastic shower curtain.
Caliper: Caliper points, or simply points, is a unit for measuring the thickness of paper. One caliper point is equal to one one-thousandth of an inch.
Grain: The orientation of fibers in paper. Paper has a natural tendency to bend "with the grain", usually making it easy to determine what grain you're working with. Grain can be either short or long, depending on whether it's going on the long or short side of the paper dimensions.
Stock: A term referring to bulk paper or board materials.
Basis Weight: The weight of one ream (500 sheets) of paper, expressed in pounds.
What is buffering?
A. Buffered material has an alkaline reserve of at least 2 percent calcium carbonate and resists the effects of acid in the environment or in memorabilia
Why is buffering important in paper products?
A. The addition of a buffering agent to paper products helps neutralise acids that come in direct contact with the paper. A buffering agent also prevents acids from migrating to other areas of the page or onto photographs. Acids that come in direct contact with your photographs could accelerate the natural aging process and cause them to discolour or fade.
http://www.archivalsuppliers.com/testimonials.asp
http://www.creativememories.com.au/MainMenu/Our-products-and-services/FAQs/Detail?folder=PAPER
http://en.wikipedia.org/wiki/Bleaching_of_wood_pulp
http://en.wikipedia.org/wiki/Mass_deacidification
http://www.howstuffworks.com/question463.htm
http://www.freepatentsonline.com/4384921.html
http://www.patentgenius.com/patent/5505819.html
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