Materials Quiz #8

What are the properties associated with average molecular weight (AMW)?

"Effects the chain length distribution" 1. The longer the "chain length", the greater the intermolecular force is. Remember the yarn in bag analogy. the longer the pieces of yarn, the more pieces stick together when picking it up from the bag. 2. AMW will affect the viscosity. increases the (T_m & T_g)

Notation for Monomers?

1. Brackets [ ] indicate a monomer 2. bonds (-) (|) indicate covalent bonding 3. n = chain length, number of repeating units (mers) = molecular weight (component) = degree of polymerization

What are the three different levels of Opacity?

1. Complete Opaque - can't see through Amorphous is 5% 2. Translucent -allowing light, but not detailed images, to pass through; semitransparent. 3. Transparent - allowing light to pass through so that objects behind can be distinctly seen. clear! Amorphous is 100%

What are Resins?

1. Describes a type of Polymer (usually in pellet form) "Two Grades" 2. Engineering Grade 3. Comodety Grade

What are the MFI Values?

1. High MFI = Low Atomic Weight 2. Low MFI = High Atomic Weight

What are the 6 elements common in plastics?

1. Hydrogen ( hydrogen & carbon = Hydrocarbon C_2 H_4 ethylene monomer) 2. Carbon 3. Nitrogen 4. Oxygen 5. Fluorine 6. Chlorine

What are the three types of polymer molecular structures?

1. Linear 2. Branched 3. Cross-linked

MFI properties with long chain polymers?

1. Longer chains = Higher Viscosities 2. Longer chains = Increased material strength 3. longer chains = Higher (T_m & T_g)

What are the density classifications of PE (polyethylene) ?

1. Low Density - PE 2. Linear Low Density - PE 3. High Density - PE 4. Ultra High Density - PE..."UHMW" ultra high molecular weight.

what are the two components of Polymer Crystallinity?

1. Semi - Crystalline 2. Amorphous

What are Monomers?

A molecule that can be bonded to other identical molecules to form a polymer. (repeating units Like A) A-A-A-A....A is the monomer repeating unit and (-) is the bond. Covalent bonds inside the mers!!

What are Elastomers? not covered in lecture.

A natural or synthetic polymer having elastic properties, e.g., rubber.

What is a Polymer?

A repeat unit is also sometimes called a mer. Mer originates from the Greek word meros, polymer which means "part"; the term polymer was coined to mean "many mers."

What are repeating units?

A repeat unit or repeating unit is a part of a polymer whose repetition would produce the complete polymer chain (except for the end-groups) by linking the repeat units together successively along the chain, like the beads of a necklace.

How to calculate Average Molecular weight?

By using a device filled with resin and heated until a weight presses on the resin and it melts and flows through an opening for a specific time. This flow rate is called the MFI (Melt Flow Rate) and is different for every different polymer.

Ethylene monomer chemical structure?

C_2 H_4

What is semi-crystalline?

Combination of ordered and disordered structures. (40% to 95%). There are ordered arrays of "Crystallites" that are interrupted by random areas of disordered Amorphous regions. Different polymers will different % of ordered parts.

what does the Cross-Linked structure look like?

Covalent bridges formed. Thermoset!

What is Degree of Polymerization?

Degree of polymerization, DP, which represents the average number of repeat units in a chain. DP is related to the number-average molecular weight

What is T_g? and what does it mean?

GLASS TRANSITION TEMPERATURE!!!!! The temperature at which the plastic starts to physically change, melt, become brittle and like glass. not good when you need a strong plastic in high heat.

What is UHMW-PE?

High Impact Resistance!! MOST USED!!!

What is a Linear Polymer?

Linear polymers are those in which the repeat units are joined together end to end in single chains. These long chains are flexible and may be thought of as a mass of "spaghetti,"

What does 'MFI' mean?

MFI - stand for 'Melt Flow Rate', and is the most common parameter specified when describing a polymer. It's just like the Modulus of Elasticity (E) for steels.

What is a Macromolecule?

Macromolecules are actually made up of even smaller subunits. Each subunit of a macromolecule is called a monomer. The macromolecules themselves are called polymers, because they are made up of many of these subunits.

What are Polymers?

Macromolecules that are long chain molecules with repeating chemical structures (UNITS, "mers")

What does Poly mean?

Many

Do all plastics have a T_m?

NO! But all thermoplastics that have a semi - crystalline structure will have a T_m.

Do Amorphous structures have a T_m?

No!

Thermoplastics?

Physical change due to Heat!

What are the two categories of Polymers?

Plastics & Elastomers (we are dealing with plastics only)

What are Branch Polymers?

Polymers may be synthesized in which side-branch chains are connected to the main ones.The branches, considered to be part of the main-chain molecule, may result from side reactions that occur during the synthesis of the polymer. The chain packing efficiency is reduced with the formation of side branches, which results in a lowering of the polymer density.

Thermosets?

Sets with Heat! Like pie in oven

what does the Branched structure look like?

Stronger than linear Lower density and more Opaque (hard to see through)

What is the Polymer Molecular Structure?

The average number of mer-units in a chain. A polymer is composed of many simple molecules that are repeating structural units called monomers. A single polymer molecule may consist of hundreds to a million monomers and may have a linear, branched, or network structure.

What is Opacity?

The condition of lacking transparency or translucence; opaqueness.

What is T_m?

The melting temperature of a polymer

Molecular Weight in monomers?

The molecular weight in monomers is calculated by adding all the individual weights of each element in the monomer. example is the molecular weight of Ethylene monomer. H=1 and C=12, total = 28 The total weight is impossible to recreate accurately every time. Need average molecular weight.

What is Polymer Crystallinity?

The packing of molecular chains to produce an ordered atomic array. Crystal structures may be specified in terms of unit cells. Crystallinity is indication of amount of crystalline region in polymer with respect to amorphous content.

What is Polymer Crystallinity?

The packing of molecular chains to produce an ordered atomic array. Crystal structures may be specified in terms of unit cells. Indication of amount of crystalline region in polymer with respect to amorphous content. Range from 0% to 95%. cannot obtain complete 100% crystallinity. Big effect on Polymers.

What is the Vinyl Chloride monomer?

The polymerization process produces "Polyvinyl Chloride" better known as "PVC" commonly used in pipes for plumbing.

What is Tetrafluoroethylene monomer?

The polymerization process produces "PolyTetraFluoroEthylene" Known as "PTFE" TEFLON!!!

What is the Propylene monomer?

The polymerization process produces "Polypropylene" (the picture does not include the brackets and n-value. )

Polymerization Process?

The process of creating a polymer!

What is Amorphous?

The random orderless regions in a polycrystalline structure.

What are the two categories of Plastics?

Thermoplastics & Thermoset

What are Thermoplastics?

Thermoplastics soften when heated (and eventually liquefy) and harden when cooled—processes that are totally reversible and may be repeated. Behavior with rising temperature.

What is a Monomer?

These long molecules are composed of structural entities called repeat units, which are successively repeated along the chain. The term monomer refers to the small molecule from which a polymer is synthesized.

What are Thermoset Plastics?

They become permanently hard during their formation and do not soften upon heating.

What is UHMW - PE?

Ultra High Molecular Weight - Polyethylene

What does Mers mean?

Units

what does the Linear structure look like?

Very flexible! higher density!

Do all plastics have a specific T_g?

Yes!!!!! (glass transition temp)

What are Cross-Linked Polymers?

adjacent linear chains are joined one to another at various positions by covalent bonds.