Student
Name:_____________ Class:_____
Synthetic Polymers
Laboratory Investigation
Student Materials
Synthetic Polymers
Student Materials
Polymers are large molecules consisting of
chains of small molecules called monomers joined together in a repeating
pattern. In
the early 1900s, scientists began to understand the chemical makeup of natural
polymers and how to make synthetic polymers with properties that complement
those of natural materials.
One simple synthetic polymer chemists developed is polyethylene. They developed it by repeating units of
the monomer ethylene (H2C=CH2). Polyethylene is a very large, zigzag-shaped molecule. One
small part of a polyethylene chain is shown below.
-(CH2- CH2)-n
H
H
H
H
H
| H | H | H |
H | H ---C | C | C | C | C | | H | H | H | H | H |
H
H
H
H
H
C 
| 
C 
| 
C 
| 
C 
| 
C---
Chemists and engineers have learned to process
and modify molecules of polyethylene in different ways to manufacture common
household products with a variety of characteristics. Polyethylene is used to make plastic trash bags, dry
cleaning bags, milk jugs and soda bottles. In industry, materials made from polyethylene are tested for
what are called stress-strain behaviors. Stress-strain behaviors include:
tensile strength - the amount of pulling force placed upon a material before it
breaks
abrasion resistance - toughness of material against scraping, scuffing
or scarring
puncture resistance - ability of a material to keep moving objects
from perforating the surface
Your Task
You and your lab partner will design an
experiment that investigates a stress-strain behavior among various plastic
products made of the synthetic polymer polyethylene.
You have been provided
with the following materials and equipment. It may not be necessary to use all of the equipment that has
been provided.
Suggested materials:
plastic dry cleaning bag coffee can
plastic kitchen wrap rubber
bands
plastic sandwich bag
ring stands/ or clamps
plastic grocery bag
ruler
ball bearings (different masses)
safety goggles
scissors
markers
sandpaper (coarse and fine)
Designing and
Conducting Your Experiment
1. In your words, state the problem you are
going to investigate. Write a
hypothesis using an If
then
because
statement that describes what you
expect to find and why. Include a
clear identification of the independent and dependent variables that will be studied.
2. Design an experiment
to solve the problem. Your experimental design should match
the statement of the problem and should be clearly described so that someone
else could easily replicate your experiment. Include a control if appropriate and state which variables
need to be held constant.
3. Review your design with
your teacher before you begin your experiment.
4. Conduct your
experiment. While conducting your
experiment, take notes and organize your data into tables.
Safety note: Students
must wear approved safety goggles and follow all safety instructions.
When you have finished, your teacher will
give you instructions for cleanup procedures, including proper disposal of all
materials.
Communicating Your
Findings
Working on your own, summarize your
investigation in a laboratory report that includes the following:
- A
statement of the problem you investigated. A hypothesis (If ... then
because
statement) that described
what you expected to find and why.
Include a clear identification of the independent and dependent
variables.
- A
description of the experiment you carried out. Your description should be clear and complete enough so
that someone could easily replicate your experiment.
- Data
from your experiment. Your data should be organized into tables, charts
and/or graphs as appropriate.
- Your
conclusions from the experiment.
Your conclusions should be fully supported by your data and address
your hypothesis.
- Discuss
the reliability of your data and any factors that contribute to a lack of
validity of your conclusions.
Also, include ways that your experiment could be improved if you
were to do it again.