Acetone dissolves the polymer, allowing the gas of the foaming agent to escape. The polymer collapses on itself and becomes more dense because the gas has removed.

a) LDPE is soft, stretchy, transparent and not very strong. Since LDPE is branched. its surface are available for contact between the molecules are weaker. Hence, the vanderwaals forces between the molecules are weaker.

b) Linear LDPE has long linear chains. Hence, the the surface area available for contact between the molecules are stronger. Hence, HDPE is usually associated with being rigid and not very flexible.

No it does not. As to plastics, the weak but extensive dispersion allow for the molecules to slip pass one another allowing the plastics to stretch and neck. This is unlike paper.

a) Non-toxic, lack of solubility, lack of reactivity and inexpensive.

b) Several types of contact lenses are made with different types of polymers. Polymers include polymethyl methacrylate (PMMA), rigid gas polymers (RGP) and Polymacon. Desirable properties include being permeable to oxygen, non-toxic, comfortable to wear and inexpensive.

c) Hard contacts are made of PMMA which is a rigid non-gas permeable plastic. Soft lenses, that have replaced them, are made of silicone. They are flexible and allows oxygen to reach the eye. As such, soft lenses are more comfortable to wear.

Acetone dissolves the polymer, allowing the gas of the forming agent to escape. The polymer collapses on itself and becomes dense, as the gas has been removed. The polymer rearranges itself and becomes more dense.

a. lacks the required strength
b. it allows for sufficient flexibility

No. For plastic, the molecules are aligned parallel to one another, in the direction of the pull. There are weak forces/attraction between the molecules, allowing them to slide across one another, although the process is not reversible and the bag will tear eventually. The paper will tear instead of stretch since the molecules in paper are held rigidly in place and are not aligned

a. bio compatible (non-soluble + non reactive to bodily fluids), non toxic, stable, cheap, tiny pore size sufficient for water vapour to pass through.

b. polymethylmethacrylate (PMMA) and polyacrylamide/silicon based polymer. Properties include transparency, flexibility, low density, tough, unreactive, lets oxygen pass through, cheap, non-toxic, durable, comfortable.

c. Hard–> PMMA (hard, rigid, not comfy. Does not let oxygen pass through. Does not contain nitrogen atoms
soft–> polyacrylamide/silicon based (similar to the polymers/silicon based. Used to make acrylic fibres for fabrics. It absorbs water, making it more flexible and comfortable for the wearer.

Structural rearrangement: From expanded, when you add acetone IMF is removed. Therefore, molecules exist singularly. Then after acetone is evaporated, new molecules form a IMF therefore leading to a new structure.

a. It is not very strong – easy to tear
Crystalline structure of LDPE is amorphous. That makes the mechanical strength of the LDPE lower than HDPE which has a uniformly crystalline domain.

b. uniformly crystalline domain allows HDPE to be much stronger. Thus, much harder to tear.

Plastic is a LDPE which is a thermoplastic material. This means it allows molecules to slip past one another allowing the plastic to stretch and cause necking.
Paper is a form from cellulose that contains a hydroxyl group. It allows formation of hydrogen bonds with oxygen on the neighbouring chain. It holds the chain firmly which causes stiffness to increase.

a. high transparency
high chemical resistance
high resistance to lipids
very good stress-cracking resistance

b. PMMA (poly methyl methylcrylate) – Hard
PHEMA (poly hydroxylethylmothacrylate) – Soft
c. Soft contact lens are gel-like plastic made of PS. Hard contact lens are PMMA lens, these are firm and durable plastic. Soft contact lens are softer and much more moist. Thus it is easier to wear and much more comfortable.

There is a lot of air in styrofoam and they get removed when immersed in acetone, leaving the denser styrofoam without air. Polymer change into a more compact structure and is thus less dense.

A. LDPE is not strong enough as compared to HDPE
B. HDPE molecules can line up to produce strength and by using a thin HDPE, it will give a strong yet flexible material.

Stretching plastic bag causes molecules to be aligned parallel to each other in direction of pull. However, paper is made of cellulose molecules that are held more rigidly in place and are not able to align. So they just break.

A. Biodegradable, stable, non-toxic, long half-life. Mechanical properties depend on its uses.
B. (PMMA) It is strong and able to retain shape.
C. Hard contact lenses contain polymethyl methacrylate with some silicon to make it flexible. They retain shape better than soft contact lens.

Acetone dissolves polymers, allowing the gas of the foaming agents to escape. The polymer collapses on itself and becomes denser as the gas has been removed.

a. LDPE cannot be used here as it lacks the required tensile strength.

b. The molecules of HDPE must line up in a formation that gives sufficient strength. Using a thin HDPE liner gives sufficient flexibility to the gloves.

Stretching the piece of plastic causes the polymer strands to take up a parallel conformation in the direction of the stretch. The irreversible structural change will at a certain magnitude of force cause the plastic to break.

Paper on the other hand, will not stretch significantly as it is made of bleached cellulose, which is more rigid in conformation. This is why they are prone to breakage instead of realignment.

a. It should be firstly chemically durable and stable, so that it will not break down in the body for a long time. Secondly it should be non-toxic, so that it will not trigger an immunological response. Thirdly it should be insoluble, so that it will not dissolve in fluid constituents. And lastly it should be unreactive, so that it will not cause blood agglutination.

b. There are many different polymers used should as polymethyl methacrylate, polymacron, 2-hydroxyethyl methacrylate. These polymers are used as they are non-toxic, permeable to oxygen and comfortable when in contact with the eye. The materials must also be easy to clean and able to conform to various eye shapes.

c. Hard lenses are usually made of polymethyl methacrylate, which is not gas permeable. Soft lenses on the other hand are usually made of silicone polymers which allows them to be more flexible and allows oxygen to come into contact with the eye. This causes soft lenses to be generally more comfortable to wear.

Styrofoam is a foaming agent and when acetone dissolves the polymer, gas is allowed to escape causing the polymer to collapse on itself thus becoming denser.

a) LDPE cannot be used in this application because it does not have the required strength.

b) The molecules of HDPE must line up in a way that produces the required strength. Using a thin liner of HDPE allows sufficient flexibility.

When the piece of plastic is stretched, the strip narrows and “necks down”. The molecules become aligned parallel to each other and in the direction of the pull. This alteration of the 3-D structure is not reversible, and if the pulling continues, the plastic breaks.
When the same pulling force is applied to a piece of paper, the paper tears rather than stretching to any significant extent. This is because the cellulose molecules in paper are held for more rigidly in place, and are not free to become aligned.

a) Durable. Good inductors. Low cost. Contains the same elements found in the human body (safe). Lack of reactivity with body fluids. Non-toxic.

b) Hard lenses are made up of PMMA. It is durable and chemically inert. On the other hand, soft lenses are made up of silicone acrylate. It is inexpensive, it has higher oxygen permeability, has good lens moisture and is comfortable to wear.

c) For hard lenses, it is able tor retain its shape easily. It requires no water to maintain their shape, thus it will not pull moisture away from the eyes leaving the eyes more moist. It is also durable as it does not tear easily.
For soft lenses, it is easily distorted when blinking as suction is removed to a certain extent. Soft lenses draw water away from eyes leading to dry eyes. It is also fragile and it tears easily because it is made of thin gel-like plastic.

Acetone dissolves the polymer, allowing gas of foaming agent to escape. This polymer collapses on itself and is more dense because the gas has been removed

a. A LDPE does not have the required strength.
b. HDPE molecules must line up in a way that produces the required strength. Using this film of HDPE allows sufficient flexibility.

The plastic molecules become aligned parallel to each other and in the direction of the pull. This alteration of the 3-D structure is not reversible. The paper will tear if pulled because the molecules are held more rigidly in place, and are not free to be aligned,which implies that the molecular interactions in paper is stronger.

a. They are – Stable over time, Non – toxic , lack of reactivity with body fluids and have appropriate permeability and process-ability for designed application.

b. PMMA(plexiglas) hard lenses.
Rigid gas permeable.
Hydrogel-polymacon.
Silicone hydrogel.

c. Hard contact lens :
PMMA, excellent optical qualties, durability and biocompatibility but no oxygen permeability.

Soft lens:
hydrogel, water – retaining and permeability of oxygen.

Styrofoam contain lots of air space, when it dissolves in acetone, the air bubbles escape and the structure will change, resulting in denser structure

a. Branching will cause the structure to be more rigid (brittle) thus it will be less flexible

b. The layers of molecules can slide between each linear HDPE, therefore making it more flexible

– The weak but extensive dispersion force allows the molecules to slip pass one another thus allowing it to stretch

– As for paper, there is different interaction which does not allow sliding between molecules

a. Non-toxic, biocompatible, non-biodegradable, lack of reactivity in body fluid

b. PMMA (Poly Methyl Methacrylate)
– Light weight
– Transparent
– Non-toxic
– Permeable to oxygen

c. Hard contact lens (PMMA) => rigid, non-gas permeable plastic
Soft (silicone) => flexible, allow oxygen to reach eyes
Due to those properties, soft lenses tend to be more comfortable.

Styrofoam contains lots of air space, when it is dissolved in acetone, the air bubbles escape and the structure will change, result in denser structure.

a. Branching will cause the structure will be more rigid (brittle) thus it will be less flexible.

b. The layers of molecules can slide between each linear HDPE, therefore making it more flexible.

– The weak but extensive dispersion force allows the molecules to slip pass one another thus allowing it to stretch.

– As for paper, there is different interaction which does not allow sliding between molecules.

a. Non toxic, bio-compatible, non-biodegradable, lack of reactivity in body fluid

b. PMMA (Poly methyl methacrylate)
– Light weight
– Transparent
– Non-toxic
– Permeable to oxygen

c. Hard contact lens (PMMA) => rigid, non-gas permeable plastic
Soft (silicone) => flexible, allows oxygen to reach eyes
Due to those properties, soft lenses tend to be more comfortable.

Styrofoam is made up of polystyrene foam. When polystyrene dissolves in acetone, air in foam is released, polymer rearranged causing it to look like massive quantity of material is being dissolved into a small volume of liquid.

a. LDPE has low tensile strength so it bends easily.

b. HDPE has less branching, resulting in more molecular forces of attraction and higher tensile strength.

No, intermolecular forces (eg. Van Der Waals and Hydrogen bonds) between chains of plastic polymers are not very strong and can be overcame easily allows chains to slide past each other when stretched.

Interaction in paper are different and much stronger as it does not have same chemical properties as plastics.

a. – Non-toxic
– Capable of maintaining a good mechanical integrity (stable)
– Capable of controlled rate of degradation
– Pore size sufficient for water vapour to pass through but kept out water droplets
(expand and stretch to form a membrane)

b. Poly (Methylmethacrylate) (PMMA)
– Non-toxic
– Permeable to oxygen
– Comfortable
– Inexpensive
– Conform eye shape and easily cleaned

c. Hard => clarity, light weight
Soft => soft, flexible, permeable to oxygen, comfortable