Measurement of Young's Modulus for plastic bag
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Measurement of Young's Modulus for plastic bag Elastic Modulus An important materials property is termed the tensile elastic modulus, or Young's Modulus. This is usually given the symbol E. Loosely; the modulus is defined as the force you need to provide to elongate your material. Measuring The Elastic Modulus The elastic modulus is measured by pulling a sample of a material in a tensile testing machine, an instrument that measures force. Let's define stress, denoted by the Greek letter (sigma), as the force (F) normalized by the cross-sectional area (A) of the material: Now attach an extensometer to the sample. The extensometer measures the change in length of the sample as it is being pulled. Let's define strain, denoted by the Greek letter (epsilon), as the change in length of the fiber normalized by the initial length. Now, plot stress versus strain. The slope of this line will give you the elastic modulus E of the material. So, the Young's Modulus is the gradient of the Graph of Force against Extension This technique applies for small forces, which do not irreversibly stretch the material. The material is in the elastic regime. Equipments * Ruler with (Range: 0-100 cm, Sensitivity: 0.1cm) * Three types of plastic bag * 100g Masses * Stand * Set square * Micrometer (Range: 0-3.5 mm, Sensitivity: 0.01mm)
Fillers are added to improve particular properties, e.g., hardness or resistance to shock. Pigments are used to impart various colours. Virtually any desired colour or shape and many combinations of the properties of hardness, durability, elasticity, and resistance to heat, cold, and acid can be obtained in a plastic. There are two basic types of plastic: thermosetting, which cannot be re-softened after being subjected to heat and pressure; and thermoplastic, which can be repeatedly softened and remoulded by heat and pressure. When heat and pressure are applied to a thermoplastic binder, the chainlike polymers slide past each other, giving the material "plasticity." However, when heat and pressure are initially applied to a thermosetting binder, the molecular chains become cross-linked, thus preventing any slippage if heat and pressure are reapplied. This is a typical Young modulus for some polymers: Polyimide 3 - 5 Polyesters 1 - 5 Nylon 2 - 4 Polystyrene 3 - 3.4 Polyethylene 0.2 -0.7 Rubbers 0.01-0.1 Tables of result Sainsbury D= 0.03mm W= 15.0 mm L= 200.0 mm Mass (g) Force (N) 1st Extension (Cm) 2nd Extension (Cm) 3rd Extension (Cm) Average (mm) 0 0 0 0 0 0 100 0.98 0.2 0.2 0.2 2 200 1.96 0.5 0.4 0.4 4 300 2.94 0.7 0.6 0.7 6 400 3.92 0.9 0.8 0.9 8 500 4.9 1.0 1.0 1.0 10 600 5.88 1.4 1.3 1.3 13 700 6.86 1.8 1.7 1.6 17 Tesco D= 0.02mm W= 15.0 mm L= 200.0 mm Mass (g)
0.25 % Width: 0.5 / 15 * 100 = 3.33 % Thickness: 0.005 / 0.03 * 100 = 16.6 % Analysis The young's Modulus can be calculated by finding each graph gradient and multiply it to its initial length and divide that by the area of the strip: * Sainsbury's: 6.86N / 17mm x 200mm / 0.45mm = 179.35 N.mm-1 * TESCO: 5.88N / 12mm x 200mm / 0.3mm = 326.67 N.mm-1 * ASDA: 5.88N / 10mm x 200mm / 0.3mm = 391.96 N.mm-1 Final results show that ASDA bag had the biggest Young's modulus of 391.96N.mm-1 closely followed by Tesco bag with 326.26 N.mm-1 and Sainsbury's had the lowest amount, 179.35 N.mm-1. As a result, Asda bag is better than Tesco's and both better than Sainsbury's plastic bags. This can be explained easily by the amount of Young's modulus for each bag. The bigger the Young's modulus is, the stronger the plastic bag is. At the molecular level what is happening is the intermolecular forces keep all molecules together and when a force try to separate them, intermolecular forces won't allow it as long as the force does not exceed the maximum level of the intermolecular forces. Once that happened, plastic bag will breaks. Companies are trying to improve the strength of the bags by changing the polymer, thickening them, or they put new elements in the polymer and many other things to improve the strength of their product.
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