2. What is LDPE ?
• Low-density polyethylene (LDPE) is
a thermoplastic made from
the monomer ethene.
3. What is a Polymer ?
• The macromolecular that are formed by
combination of one or more than two types of
innumerable simple molecules by chemical bond
formation are called Polymers.
• One or more than two type of innumerable
simple organic molecules that combine with one
another & form a polymer are called monomers.
• The reaction process of one or more than two
innumerable simple organic molecules that
combine with each other by Chemical bond
formation is called Polymerisation
4. Types of Polymer Substance
Polymer substance are classified in different types.
• Naturally occurring Polymer Substances- The polymers obtained
from nature (plants and animals) are called natural polymers. These
polymers are very essential for life. For e.g.: Cellulose, Proteins,
Starch, Nucleic acid- DNA & RNA
• Semisynthetic Polymer Substances-Semisynthetic Polymer are
obtained by chemical reaction with Polymeric substance occurring
in nature. The rubber with improved properties obtained by
vulcanization of natural rubber is used in the formation of tyres.
• Synthetic Polymer Substance -The polymers which are prepared in
the laboratories are called synthetic polymers. These are also called
man made polymers. For e.g.: polyethene, PVC nylon, teflon,
bakelite terylene, synthetic rubber etc.
5. Classification of Polymers
HOMOPOLYMER & CO-POLYMER
• Homopolymers: These consist of chains with
identical bonding linkages to each monomer
unit. These may be represented as: -[A-A-A-A]-
• Copolymer : These consist of chains with two
or more linkages usually implying two or more
different type of monomer units. Thes may be
respresented as:-[A-B-A-B-A-B]-
6. Polymer Classified by mode of
Polymerzation
• Addition Polymers: The monomer molecules
bond to each other without the loss of any
other atoms.
Eg : Ethylene--- CH2=CH2 ----->~~CH2-CH2-CH2-CH2~~ Polyethylene (PE)
• Condensation Polymers: Usually two different
monomer combine with the loss of a small
molecule, usually water.
Eg :
9. Types of Polyethene
• Low Density Polyethylene (LDPE)
• Linear Low Density Polyethylene
(LLDPE)
• Medium Density Polyethylene
(MDPE)
• High Density Polyethylene (HDPE,
aka HD)
10. Properties of LDPE
MECHANICAL PROPERTIES OF LDPE
• It has more open structure due to presence of a small amount of
branching in the chain (on about 2% of the carbon molecule).
It is translucent to opaque, strong, tough & enough to be virtually
unbreakable and at the same time quite flexible.
CHEMICAL PROPERTIES
• Chemically LDPE is uncreative at room temperature, slowly attacked
by strong oxidizing agents and some solvents will cause softening or
swelling.
• It may be used at temperatures up to 95° Celsius for short periods
and at 80° Celsius continuously.
11. Surface Property Modifiers
• Sleep & Blocking Agent – Prevent film & sheet sticky
• Anti Static Agent – Prevent static charges on surface
• Anti Fogging Agent – Disperse moisture droplets on film
12. Aesthetic property
• Dyes and pigments - impart color
• Odorants - add fragrance
• Deodorants - prevent development of odor
13. Other LDPE Properties
• Films are soft and clear
• Good for heat-sealing
• Fair moisture barrier, very poor oxygen barrier.
• Very high elongation (desirable for stretch wrap)
• Translucent, very tough, weatherproof, good chemical
resistance, low water absorption.
15. Applications of LDPE
• Agriculture – for protection of delicate crops from
extreme weather conditions.
• Lining of Canal, reservoir, ponds from leakage loss.
• Packaging and wrapping.
• Water roofing for terrace gardens.
• For protection of food grains, fertilizers, cotton,
chemicals, cement, constructions etc.
16. Testing Procedure of LDPE Bags
• A tensile test, also known as tension test and it is
most fundamental type of mechanical test which can
perform on material.
By pulling on something, very quickly determine how
the material will react to forces being applied in
tension. As the material is being pulled, one can find
its strength and stretch.
17. • Tear Strength Test (Tear Testers)
Tear testing is a measurement of the resistance of sheet type
materials to tearing. A common approach is to apply a tension load
to a sample that has been prepared with a cut to begin the
controlled tear.
Dart Impact Test
Falling dart impact is a traditional method for evaluating the impact
strength or toughness of a plastic film. This test uses a single dart
configuration and a single drop height, while change the weight of
the dart. Test results can be used either as a quality control
evaluation or for end use comparisons.
18. Recycling
• After individuals drop LDPE products off
at a recycling center, the recycling company
melts the plastic to eliminate contaminants.
• After putting the low density polyethylene
under heat, the material is fashioned into thin
plastic sheets, which the recycling company
then sells to manufacturers.
