BSI Education

Practice Assignment 12

Paper properties: strength and impact resistance

Different papers have different properties. So we use different papers for different purposes. Paper tissues have to absorb water, and they mustn’t be too weak even when they are wet.

This activity requires you to produce a ‘consumer report’ comparing two different makes of paper tissues.

Part A: Comparing the strengths of papers

What you have to do

  1. Find out the cost of each make of tissue, and the number of tissues per box.
  2. Get a copy of Standard Procedure SP0012-1:2005. Read it carefully. Note that you do not need to do all of the procedures described. You are only testing how easily the tissues tear.
    • There is no need to attach a pin to the specimen or to see how much it stretches.
    • There is no need to plot a graph of these results.
    • Limit your measurements to comparative tensile strength, and not absolute tensile strength. This means that you don’t have to worry about the thickness of the specimens, though you still need to know the width.
    • Ensure that your box of crumpled paper is large enough to catch the masses as they fall.
  3. Before starting:
    • read the standard procedure and the hints below carefully;
    • check that a risk assessment has been carried out;
    • list the equipment and materials you need
  4. Make and record measurements of comparative tensile strength for dry and wet tissues. Repeat your measurements and find mean values for dry and wet material. You could write your measurements into tables like this. Use a different table for each make of tissue.

Name of make of tissue

Cost of tissues per box

Number of tissues in full box

Cost per tissue

 

Repeated measurements Width test sample Wet or dry Mass hung when breaking happens, in kilograms Force needed to break, in newtons* Comparative tensile strength* Mean comparative tensile strength
1st measurement   Wet        
2nd measurement   Wet      
3rd measurement   Wet      
1st measurement   Dry        
2nd measurement   Dry      
3rd measurement   Dry      

* Remember, the Standard Procedure tells you that:

 Force in newtons = Mass in kilograms x 9.8
andComparative tensile strength =   Force in newtons   (at breaking point)
 Width in millimetres

  1. Explain how the two makes of tissue compare on value of money as far as comparative tensile strength is concerned.

Some hints

  • For wet tissues, use just enough water to dampen them. Place the tissues on a clean dry surface each time. Use the same amount of water for each one.
  • It is important to repeat measurements and calculate means. The mean value of a set of measurements can even out random variations. This makes the result more reliable.
  • Note that you need to adapt what you do, depending on how the specimen behaves. You may need to vary the width of the specimens.
  • 100 grams = 0.1 kilograms
  • 10 grams = 0.01 kilograms

Part B: Comparing the impact resistance of papers

What you have to do

  1. Get a copy of Standard Procedure SP0012-2:2005. Read it carefully.
  2. Using the Procedure, measure the mass and drop height at which the tissue tears.
  3. Note: You do not need to measure the thickness of the tissue. Assume both makes have the same thickness.
  4. Calculate the impact-failure energy for dry tissue and wet tissue. Record your results in a table like the one below.
  5. Repeat the measurements and calculate mean values.

Make of tissue

 

Repeated measurements Wet or dry Dropped mass when sample breaks, in kilograms Drop height, in metres Impact failure energy, in joules* Mean impact failure energy, in joules
1st measurement Wet        
2nd measurement Wet      
3rd measurement Wet      
1st measurement Dry        
2nd measurement Dry      
3rd measurement Dry      


*Remember, the Standard Procedure tells you that:

Impact failure energy = dropped mass when sample breaks x drop height x 9.8

  1. Explain how the two makes of tissue compare for value for money as far as impact failure energy is concerned.

Some hints

  • Note that you need to adapt what you do, depending on how the specimen behaves. You may need to vary the size of the masses used or the drop height.

Some questions

  1. Some of the variables used in these investigations are: mass, width, force, comparative tensile strength, height, impact-failure energy. Make a table of these variables to show the unit for each one.
  2. Name another material that must have high tensile strength. Give an example of a use of the material that depends on this.
  3. Tissues can be described by manufacturers as ‘soft but strong’. Find out if the ‘soft but strong’ description is something that is tested against standards or is it just a good advertising catch-phrase?

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