Material Selection using CES EduPack

2. Introduction
A plastic bag, polybag, or pouch is a type of container made
of thin, flexible, plastic film, nonwoven fabric, or plastic
textile. Plastic bags are used for containing and transporting
goods.

3. Objective and scope
•To investigate the material used to produce
the plastic bag.
•To understand the manufacturing process
used to produce the plastic bag.

4. Material Selection using CES EduPack
• Must be a polymer – low cost, moldable
• It must be thermoplastics – easy to manufacture, soften during heating
unlike thermosets

5. Step 1 : Plot graph of price against density
All types of materials

6. Step 2: Restrict the material search under
thermoplastic’s range
All polymers
(Thermoplastics)

7. Step 3: Limit the density and price, choose the
lowest
Polymer with the lowest density and price

8. Process Selection using CES EduPack
• Limit restriction for process search under PE
• Develop graph Hollow 3d against production rate
Injection molding is rejected
since it requires finishing for
the product compared to
blow molding

9. Material Content Of A Plastic Bag .
• Made with a variety of plastics films.
• The main material: POLYETHYLENE (LLDPE or LDPE)
• Composition: (-CH2-CH2-)n
• Made up of colourless high-density polyethylene or low-
density polyethylene.

10. Manufacturing Process Of Plastic Bag – FILM
BLOWING PROCESS
• Typically, blown film extrusion is
carried out vertically upwards,
however horizontal and downward
extrusion processes are now
becoming more common. Figure 2
shows a schematic of the set-up for
blown film extrusion.

11. Step Of Film Blowing Process
• This procedure consists of four main steps:
1. The polymer material starts in a pellet form, which are successively compacted and melted to
form a continuous, viscous liquid. This molten plastic is then forced, or extruded, through an
annular die.
2. Air is injected through a hole in the center of the die, and the pressure causes the extruded melt
to expand into a bubble. The air entering the bubble replaces air leaving it, so that even and
constant pressure is maintained to ensure uniform thickness of the film.
3. The bubble is pulled continually upwards from the die and a cooling ring blows air onto the
film. The film can also be cooled from the inside using internal bubble cooling. This reduces the
temperature inside the bubble, while maintaining the bubble diameter.
4. After solidification at the frost line, the film moves into a set of nip rollers which collapse the
bubble and flatten it into two flat film layers. The puller rolls pull the film onto windup rollers.
The film passes through idler rolls during this process to ensure that there is uniform tension in
the film. Between the nip rollers and the windup rollers, the film may pass through a treatment
center, depending on the application. During this stage, the film may be slit to form one or two
films, or surface treated.

12. Advantage And Disadvantage Of Film Blowing Process
Advantages Disadvantages
1) Low costs
Extrusion blow molding uses a lower level of pressure, which means that
machinery costs are low, making it easier and more cost-efficient to mold
external threads or open-ended and large parts, which can be split by
opening a closed molding. Moreover, It is also reduce labor costs.
1) Highly dependent on petroleum
Like the gas industry, the blow molding sector highly relies on millions of
gallons of petroleum to be able to produce plastic product. As oil is an
essential factor in thermoplastics that is becoming automated and more
streamlined, the technology has become an ongoing threat to the
diminishing oil supply in the world.
2) High productivity
It allows manufacturers to produce greater quantities in just a short
period of time. Using machines that allow for 3D moldings, it has allowed
for a production cycle that is much faster.
2) Huge impact on the environment
As this technology depends greatly on petroleum and is an integral part in
producing polymer, it carries a huge risk on the destruction of the
environment. Aside from the fact that it contributes to the diminishing oil
resources, it creates plastic that is not biodegrade. In a sense, it can
increase plastic production, but it cannot remove the environmental risks
its products bring.
3) Variety of products can be produced
It allows engineers to try and create a variety of applications and designs,
which resulted to multiple interesting uses. Example of products
produced: fuel tanks, seat support for vehicles, flower pots and toy
wheels.
3) Limited uses
Considering that blow molding is limited to hollow forms, such as bottles
and plastic containers, and air pressure is essential to the process, it
would come with limited uses. For example, it will experience difficulties
with wall thickness, which is difficult to control.

13. Conclusion