题目内容
（请给出正确答案）
Plywood is an example of
A) Laminar composites
B) Sandwich composites
C) Particulate composites
D) Foam Composites
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更多“Plywood is an example of A) La…”相关的问题
A、the future life
B、the wheel of the Law
C、the passing days
D、the traditional culture
A．柳条箱；皮重；单价 B．柳条箱；风干重量；货物重量
C．胶合板箱；风干重量；单价 D．胶合板箱；皮重；货物总值
A) We are surrounded by so much paper and card that it is easy to forget just how complex it is. There are many varieties and grades of paper materials， and whilst it is fairly easy to spot the varieties， it is far more difficult to spot the grades.
B) It needs to be understood that most paper and card is manufactured for a specific purpose， so that whilst the corn-flake packet may look smart， it is clearly not something destined for the archives. It is made to look good， but only needs a limited life span. It is also much cheaper to manufacture than high grade card.
C) Paper can be made from an almost endless variety of cellulose-based material which will include many woods， cottons and grasses or which papyrus is an example and from where we get the word "paper". Many of these are very specialized， but the preponderance of paper making has been from soft wood and cotton or rags， with the bulk being wood-based.
Paper from Wood
D) In order to make wood into paper it needs to be broken down into fine strands. Firstly by powerful machinery and then boiled with strong alkalies such as caustic soda， until a fine pulp of cellulose fibers is produced. It is from this pulp that the final product is made， relying on the bonding together of the cellulose into layers. That， in a very small nutshell， is the essence of paper making from wood. However， the reality is rather more complicated. In order to give us our white paper and card， the makers will add bleach and other materials such as china clay and additional chemicals.
E) A further problem with wood is that it contains a material that is not cellulose. Something called lignin. This is essential for the tree since it holds the cellulose fibres together， but if it is incorporated into the manufactured paper it presents archivists with a problem. Lignin eventually breaks down and releases acid products into the paper. This will weaken the bond between the cellulose fibers and the paper will become brittle and look rather brown and careworn. We have all seen this in old newspapers and cheap paperback books. It has been estimated that most paper back books will have a life of not greater than fifty years. Not what we need for our archives.
F) Since the lignin can be removed from the paper pulp during manufacture， the obvious question is "why is it left in the paper?" The answer lies in the fact that lignin makes up a considerable part of the tree. By leaving the lignin in the pulp a papermaker can increase his paper yield from a tree to some 95%. Removing it means a yield of only 35%. It is clearly uneconomic to remove the lignin for many paper and card applications.
G) It also means， of course， that lignin-free paper is going to be more expensive， but that is nevertheless what the archivist must look for in his supplies. There is no point whatsoever in carefully placing our valuable artifacts in paper or card that is going to hasten
their demise. Acid is particularly harmful to photographic materials， causing them to fade and is some cases simply vanish!
H) So， how do we tell a piece of suitable paper or card from one that is unsuitable? You cannot do it by simply looking， and rather disappointingly， you cannot always rely on the label. "Acid-free" might be true inasmuch as a test on the paper may indicate that it is a neutral material at this time. But lignin can take years before it starts the inevitable process of breaking down， and in the right conditions it will speed up enormously.
I) Added to this， as I have indicated earlier， paper may also contain other materials added during manufacture such as bleach， china clay， chemical whiteners and size. This looks like a bleak picture， and it would be but for the fact that there are suppliers who will guarantee the material that they sell. If you want to be absolutely sure that you are storing in， or printing on， the correct material then this is probably the only way.
J) Incidentally， acids can migrate from material to material. Lining old shoe boxes with good quality acid-free paper will do little to guard the contents. The acid will get there in the end.
Paper from Rag
K) Paper is also commonly made from cotton and rag waste. This has the advantage of being lignin-free， but because there is much less cotton and rag than trees， it also tends to be much more expensive than wood pulp paper. You will still need to purchase from a reliable source though， since even rag paper and card can contain undesirable additives.
L) A reliable source for quality rag papers is a recognized art stockiest. Many water color artists insist on using only fine quality rag paper and board.
M) The main lesson to learn from this information is that you cannot rely on purchasing archival materials from the high street. The only safe solution is to purchase from specialist suppliers. It may cost rather more， but in the end you will know that your important and valuable data and images have the best home possible.
1. The corn-flake packet is cheaper than high grade card.
2. There are a lot of materials which can be used for making paper， but the superiority ones are soft wood， cotton and rags.
3. During the whole manufacturing process， the final product is made from a pulp of cellulose fibres.
4. In order to make white paper and card， the makers will add bleach.
5. Liguin is essential for the tree but it will make paper easy to break.
6. Many paper producers will preserve lignin during manufacture， because leaving the lignin will make more paper from a tree.
7. Acid is particularly harmful to photographic materials.
8. If the lignin is removed from the paper， the paper will be more expensive.
9. Although free of lignin， paper made from cotton and rag waste can also cost more money than wood pulp paper because there is much less cotton and rag than trees.
10. What we can learn from "Paper from Rag" is that you had better buy archival materials from specialist suppliers.
A) Compression molding
B) Reaction inj ection molding
C) Resin transfer molding
D) Filament winding
A) netting index
B) vulcanization
C) polymerization
D) hardness
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