Category Chemistry

HOW STRONG IS CARDBOARD MADE?

Cardboard is really just very thick paper. The machine that makes it is slightly different because the card is not wound onto a reel at the end, but cut up into sheets. For making strong, light boxes, corrugated cardboard is often used. This has paper pressed into a ridged shape sandwiched between two outer sheets.

We’ll discuss how strong cardboard boxes are, and why they are important for being able to carry anything.

The truth is, they seem disproportionally strong, and many are able to hold up to anything from 30 to 80 pounds, depending on both size, and quality, but if you get a double-walled cardboard box, you can minimally put about 60 pounds in there, up to 150 pounds in item weight. That’s huge!

How does this work? Cardboard is a single corrugated sheet, and a single wall one is made from kraft paper and glue, and three sheets are essentially stuck together with an adhesive of cornstarch, and then folded into the shape of a box, and from there assembled.  This might seem so simple, but it allows for a strong container.

So, how does it get the strength that it does? The secret is the construction of it, which is easier to understand when you equate it to normal construction processes.  You can imagine something being created? With pillars, beams, and the like, you’ll notice that those tend to be much smaller than the rest of the building, but they are capable of adding valuable and necessary support to a structure that would otherwise collapse.  Those small parts are what keep it together.

The corrugated parts of this are what help with strength, and the middle, in turn, acts as a type of support that allows for strength to be utilized to the outer sheets as well. Standard steel I beam, for example, is simple, but it has a design that allows for lots of support. The same is for cardboard.  The small corrugated areas are essentially tiny I-beams, and it works in the same way a bridge does, where it uses truss structure to bring more strength to both the interior and the exterior walls, so you’ll get double walled cardboard that’s much stronger than others.

Picture Credit : Google

WHAT KIND OF PLANT FIBRE IS USED TO MAKE PAPER?

Nowadays most paper is made from specially grown trees. These trees are usually softwoods, grown in the cooler parts of the world where little else can thrive. Fir, pine, spruce, larch and cedar trees are all used. The trees do not have to be very tall or straight, as they do for timber. Almost all parts of the tree, except the bark, can be ground up into fibres for papermaking.

Most plant materials also contain nonfibrous elements or cells, and these also are found in pulp and paper. The nonfibrous cells are less desirable for papermaking than fibres but, mixed with fibre, are of value in filling in the sheet. It is probably true that paper of a sort can be produced from any natural plant. The requirements of paper quality and economic considerations, however, limit the sources of supply.

Pulped forest tree trunks (boles) are by far the predominant source of papermaking fibre. The bole of a tree consists essentially of fibres with a minimum of nonfibrous elements, such as pith and parenchyma cells.

Forests of the world contain a great number of species, which may be divided into two groups: coniferous trees, usually called softwoods, and deciduous trees, or hardwoods. Softwood cellulose fibres measure from about 2 to 4 millimetres (0.08 to 0.16 inch) in length, and hardwood fibres range from about 0.5 to 1.5 millimetres (0.02 to 0.06 inch). The greater length of softwood fibres contributes strength to paper; the shorter hardwood fibres fill in the sheet and give it opacity and a smooth surface.

Since cellulose fibre is a major constituent of the stems of plants, a vast number of plants represent potential sources of paper; many of these have been pulped experimentally. A rather substantial number of plant sources have been used commercially, at least on a small scale and at various times and places. Indeed, the use of cereal straws for paper predates the use of wood pulp and is widely practiced today throughout the world, although on a relatively small scale of production. Because many parts of the world are deficient in forests, the development of the paper industry in these areas appears to depend to a considerable degree upon the use of annual plants and agricultural fibres.

Nonwoody plant stems differ from wood in containing less total cellulose, less lignin, and more of other materials. This means that pulps of high cellulose content (high purity) are produced in relatively low yield, whereas pulps of high yield contain high proportions of other materials. Papers made from these pulps without admixture of other fibre tend to be dense and stiff, with low tear resistance and low opacity.

The morphology (form and structure) of the cells of annual plants also differs considerably from wood. Whereas the nonfibrous (parenchyma) cells of coniferous wood constitute a minor proportion of the wood substance, in annual plants this cell type is a major constituent. As hardwoods also often contain considerable amounts of nonfibrous cells, there is a closer resemblance between hardwood pulps and pulps from annual plants.

Picture Credit : Google

Some activities based upon Chemicals.

Chemicals surround us all the time and influence our lives without us even noticing. Here you can see a few more examples of some chemical and physical reactions with everyday chemicals.

Producing gas

Many different chemical reactions produce gas. At home, why not try producing carbon dioxide gas. To do this, mix together vinegar, which is acidic, and baking powder, which is alkaline, in a jar. Make sure the jar is in a sink — watch the bubbles of carbon dioxide erupt over the edge of the jar!

Physical change

Iron filings and sulphur can be mixed together. The iron filings can be easily separated from the mixture as they are attracted by a magnet. This is an example of a physical change. In a physical change, the material changes only its appearance. It is easy to reverse the change because no new substances are formed.

Chemical change

Eggs and bread are mixtures of compounds. When they are heated, new compounds are formed and a chemical reaction has taken place. We cannot undo this change in a simple way. Only complex chemical processes can reverse a chemical change.

How does evaporation work?

Ask an adult to help you boil a solution of salt and water. As the solution is heated, the tiny molecules move more rapidly. The water molecules eventually gain enough energy to fly off as gas. However, there’s not enough energy for the salt to boil, and it is left behind.

 Picture Credit : Google

What are various uses of chemicals?

People have always used natural chemicals in their daily lives. Vegetable dyes are used to colour wool and cloth or to make paint. Other chemicals from plants have been used as medicines. Originally, drugs such as penicillin were made from moulds grown naturally. Today, most of our medicines are artificially produced.

Scientists have produced chemicals to help farmers. Fertilizers, spread on the fields, make crops plentiful and strong. Pesticides can be used to kill insects that damage crops. Although chemicals are used to improve our lives, many may be harmful too. For this reason, chemicals are developed and tested in laboratories before they are used.

            Pesticides are sprayed on crops to protect them from being eaten by insects.

 Picture Credit : Google

How can we check the nature of chemical without going to Lab?

Red cabbage contains a coloured chemical which acts as an indicator. The blue dye from the cabbage turns pink in acids and green in alkalis. Neutral substances do not make the indicator change colour. Make your own indicator and find out which of the everyday chemicals you have at home are acids or alkalis.

What you need

Red cabbage, a knife, a chopping board, boiling water, 2 bowls, blotting paper, a wooden spoon, clothes pegs, string, milk, soap, lemon juice, bicarbonate of soda and water.

Ask a grown-up to boil some water and chop the cabbage leaves. Put the cabbage leaves in a bowl.

Carefully add the water to the cabbage leaves. Stir the mixture using a wooden spoon. The dye from the cabbage will turn the water blue.

When the solution has cooled, pour the water into another bowl. You don’t need the cabbage leaves anymore.

Dip strips of white blotting paper into the indicator solution. When they are soaked in dye hang them up to dry using string, tied between two points, and some clothes pegs.

Use your indicator paper to test any liquids you may have. (You can also test solids dissolved in water). Just place a few drops of each chemical onto a fresh piece of indicator paper. Try testing chemicals such as soap, milk, lemon juice, and bicarbonate of soda mixed with water. Different substances turn the paper different colours.

 Picture Credit : Google

Does Air contain chemical?

Air is a mixture. It contains many gases including nitrogen, oxygen and carbon dioxide. Nitrogen combines with other elements to make compounds called ‘proteins’. Proteins help plants and animals grow, and animals need oxygen to breathe. At the top of a mountain, there is less air than at the bottom. For this reason, mountain climbers sometimes need to take extra oxygen with them.

In sunlight, plants grow by combining carbon dioxide and water to produce more of the chemicals of which they are made. Gases in the air are being used all the time, but they never run out!

The Gas Cycle

We take oxygen from the air, but put back carbon dioxide. Plants take carbon dioxide from the air and, during the day, put back oxygen. Plant and animal bodies contain nitrogen. When they die, this nitrogen returns to the air or soil. Oxygen, carbon dioxide and nitrogen are constantly recycled so we never run out!

            Fighter pilots take their own oxygen supply with them as there is very little air at high altitudes.

            Plants and animals depend on each other to produce the chemicals needed for survival.

 Picture Credit : Google