Group 6 Presentation Chapter 7, 8, and 9. Gavin Kurey Kevin Archibeque David Barboza Cedric Turcotte Marcos Gonzales. Overview of Presentation:. Structure, General Properties, and Applications of: Polymers (Ch. 7) Ceramics, Graphite, and Diamonds (Ch. 8) Composite Materials (Ch. 9).
Structure, General Properties, and Applications of:
Polymers (Ch. 7)
Ceramics, Graphite, and Diamonds (Ch. 8)
Composite Materials (Ch. 9)
Pictures from Accelrys
Background of Polymers
Characteristics of Polymers
The Structure of Polymers
Types of Plastics and Rubbers
Polymer – Poly meaning many and mer meaning unit.
Monomers – Basic building block of a polymer.
Macromolecules – extremely large collections of molecules to form one unit.
Plastics – a synonym for polymers.
Synthetic – manmade.
The word plastic comes from the Greek word plastikos, meaning capable of being molded and shaped.
The earliest polymers, such as cellulose, were made from natural organic materials from animals and vegetable products.
The development of modern polymer technology began in the 1920’s when raw materials necessary for making polymers were extracted from coal and petroleum products. Ethylene was the first example of such raw material.
Plastics contain large molecules
Two common examples of how plastics can be shaped are:
Advantages of using plastics:
Low Electrical and Thermal Conductivity
High Strength-to-Weight Ratio
Resistance to Chemical Corrosion
Amount of Noise Reduction
Assortment of Colors and Transparencies
Ease of Manufacturing
Minimal Additional Surface Treatments
Forms of Availability Such As: Tubes, Films,
Sheets, Plates, Rods, etc.
Molecular Weight Distribution (MWD), is the sum of the molecular weights of the mers in a chain
Degree of Polymerization (DP), is the size of the polymer chain
MWD and DP determines the tensile strength, impact strength, and viscosity of polymers.
An increase in MWD, increases:
Resistance to cracking
The larger DP, the larger:
Cost (because harder to shape)
Polymers are very large molecules compared to most other organic materials
They are long chain of molecules linked together by a process called polymerization.
There are two important types of Polymerization:
Known as Step-Growth or Step Reaction
Is the process in which polymers are produced by the formation of bonds between two types of reacting mers. In better terms, the polymer grows step-by-step until all of one reactant is consumed.
Example: Water is condensed out to make plastic.
Known as chain-growth or chain-reaction
Much faster than condensation method
Is the process in which the chain-growth takes place without reactant by-products such as water
An initiator is added to the reaction to open the double bond between the two carbon atoms
Increase resistance to deformation and stress cracking.
Cross Linked Polymers
(Thermosets) have a major influence in polymers. Imparting hardness, strength, stiffness, brittleness, and better dimensional stability.
(highly cross linked), have a higher strength when exposed to high energy radiation, UV light, x-rays, or electron beams.
Copolymers contain two types of polymers
Ex: Styrene-butadiene, used in making tires
Terpolymers contains three types of polymers
Ex: Acrylonitrile-butadiene-styrene, used to make helmets
Amorphous, the polymer chains exist without order.
Crystallites, the regions arrange themselves in an orderly manner.
As Crystallinity increases polymers become:
to solvents and heat.
Polymers that can undergo external shaping forces and return to their original state
Ex: Acrylics, Nylons, Polyethylenes
Characteristics and Effects on Thermoplastics:
Effects of Temperature
Rate of Deformation
Thermal and Electrical Properties
Glass-Transition Temperature (Tg)
Above the Tg, the thermoplastic gradually softens and eventually turns into a viscous fluid.
Repeated heat-cycling causes thermal aging or degredation.
Effects of Temp. on thermoplastics is similar to that of metals, (for increased T, Increased toughness, strength/modulus of elasticity decreases)
Thermoplastics can undergo large uniform deformation in tension before fracture.
This characteristic allows for thermoforming.
Complex shapes can be made, like bottles, meat trays, etc.
Under deformation, the molecules within thermoplastics align themselves in unison with the deformation.
This is called Orientation.
The specimen becomes anistropic
Important for enhancing strength and toughness properties
Most thermoplastics are susceptible to Creeping and/or stress relaxation
This can even occur at room temperature!
Localized, deformed areas that are wedge-shaped that occur under stress
Sometimes appearing to be cracks, crazes are usually comprised of voids (50%).
Caused by enviroment stress or other external forces, like solvents.
Polymers absorb water
Water acts as a plasticizing agent
Tg, elastic modulus, and yeild stress are all lowered when water is absorbed
low thermal/electrical conductivity and a high coefficient of thermal expansion
Good as insulators and packaging for electronics
Electrically conducting Polymers (metal powders, iodides, salts)
Thermally conducting Polymers (nonmetallic, conductive particles;100x more conductive)
When long chain molecules in a polymer become one giant molecule with strong covalent bonds and is from then on permanently set.
The curing reaction of a thermoset is irreversible, unlike thermoplastics
No set Tg value, rate of deformation, or response to temperature.
Achieved by reducing secondary bond strength
Most common use of a plasticizer is found in PVC (Polyvinylchloride)
Compounded into plastics and rubbers
Protects against Oxidation and Ultraviolet Radiation
Reduces overall cost of a polymer
May improve hardness, toughness, stiffness, abrasion resistance, etc
Common fillers include: Saw Dust, silica flour, clay, mica, talc, asbestos, etc
Organic or Inorganic
Colorant selection depends on service temperature and light exposure.
Pigments have a higher tolerance to temp and light.
Additives to reduce the flammability of a polymer
Common additives include phosphorus, chlorine, and boron
Cross-linking reduces flammability as well
Added to reduce friction during processing.
Typical lubricants are: Linseed oil, mineral oil, waxes, metallic soaps, etc
Very important to keep thin polymer sheets from sticking to each other
Biodegrability - microbial species can decompose the object over time
Three different biodegradable plastics have been developed thus far: Starch-based, Lactic-based, and Fermented Sugar Systems.
Thermoplastics can be recycled by melting them down and reshaping them into new products
Also known as Rubber
Ability to undergo large elastic deformations without rupture
Highly kinked structure
Stretch under load, but return to original shape without load
Vulcanization (cross-linking w/ sulfur)
Types of elastomers: Natural Rubber, Synthetic Rubber, Silicones, Polyurethane
Definition: Ceramics are compounds of metallic and non-metallic elements
Two Major Categories:
Traditional such as whiteware, tiles, bricks, and pottery.
turbines, cutting tools, and aerospace applications.
Cubic Boron Nitride
It is the second hardest known substance.
Synthetically made in a manner similar to synthetic diamonds.
It is not found in nature.
It is often used in cutting tools and abrasive wheels.
Because of their strength and inertness the most common uses include replacement for human joints, prosthetic devices and teeth crowns.
Types of Glasses
Properties of Glasses
Types of Graphite
Glass- an amorphous solid with the structure of a liquid.
Glass is an inorganic product of fusion that has been supercooled to a rigid condition without crystallizing.
Supercooled- the cooling of a liquid at a rate too high to allow crystals to form.
Soda-lime glass- The most common type of commercial glass.
Fused silica glass
Fused silica glass
Glass is categorizied by its:
Resistance to thermal shock
Opaque (White or Translucent)
Photochromatic (Darkens with light exposure)
Photosensitive (Changing from clear to opaque
Fibrous (Constructed of long fibers)
Foam or cellular (containing bubbles)
Hard or Soft (Thermal hardness)
Elasticity (Modulus of elasticity 55 to 90 GPa)
Scratch Resistance (350 to 500 HK)
Glass Ceramics have a higher crystalline component than that of glass.
This increase in crystalline is due to the Devitrification of the glass.
Devitrification- is the recrystallization of glass which occurs due to the heat treating of the glass after the desired shape is constructed.
Glass Ceramics have a hardness of 520 to
650 HK, which is significantly larger than the hardness of typical glass (350 to 500 HK).
High resistance to thermal-shock, due to their non-zero coefficient of thermal expansion
Extremely strong due to the absence of porosity; which is typically found in traditional ceramics
Glass ceramics are commonly used for cookware, heat exchangers in gas turbines engines, housing for radar antennas, and other electrical applications.
Graphite- a crystalline form of carbon having a layered structure with basal planes or sheet of close-packed carbon atoms.
Lampblack (black soot) is an amorphous graphite that is used as a pigment
The strength and stiffness of graphite increases with temperature
High electrical and thermal conductivity
Good resistance to thermal shock and high temperature
High resistance to chemicals
Graphite Fibers- used to reinforce plastics
Carbon and Graphite Foams- used for core material for aircraft and ship interior panels, structural insulation, sound absorption panels, lithium-ion batteries, and for fire and thermal protection
Buckyballs- solid lubricant particles that are made from lampblack (black soot)
Nanotubes- used as a natural building material for new microelectromechanical systems
Diamond- a principal form of carbon with a covalently bonded structure
Hardest substance known (7000 to 8000 HK)
Very brittle, starts to decompose in air at 700oC
A composite material is a combination of two or more chemically distinct and insoluble phases with recognizable interface, in such manner that its properties and structural performance are superior to those of the constituents acting independently.
(Book definition p.238)
First engineering application 1907:
acid-resistant tank (Phenolic resin with asbestos fibers)
Steel-wire reinforced tires;
Snow boards / skis;
2 x more resistant (compression)
Brake pads / rotors;
High performance racing body parts;
Don’t get confused by the PLASTIC appellation.
Reinforced plastics: also know as polymer-matrix composites&fiber-reinforced plastics.
1 . Fibers (discontinuous)
2. Matrix (continuous)
Known as a slender, elongated, threadlike object or structure
They combine high strength and high stiffness.
Graphite – Glass – Boron – Polymer;
Others (boron carbide, steel, aluminium oxide, etc.)
When more then two fibers are used, the composite is called a hybrid.
Percentage of fibers in reinforced plastics varies from 10% to 60%. Anything higher then 65% usually result in lower structural properties.
Fibers are sometimes treated with a coating to increase bonding strength between fiber and matrix.
Cross-section usually less then 0.0004 in. (hair =0.001in)
Sensible to defects
Short & long fibers:In a given type of fiber, if the mechanical properties improve as a result of increasing the average fiber length, then it is call a short fiber. Otherwise it’s a long fiber.
Continuous fibers: Offers a better control on composite’s reaction. Generally use for oriented forces or for increased properties.
Known as the bonding substance.
Tough and generally chemically inert.
Support the fibers in place and transfer the stress to them while they carry most of the load;
Protect the fibers against physical damage and the environment;
Reduce the propagation of cracks in the composite by virtue of the greater ductility and toughness of the plastic matrix.
Thermosets: epoxies (80%) – polyester - silicon
Thermoplastics:Polyetheretherketone; thougher then thermosets, but lower temperature resistance;
Metals: aluminium – magnesium - titanium
Ceramics: silicon carbide/nitride – aluminium oxide - mullite
The mechanical and physical properties of reinforced plastics depend on type, shape, and orientation of the reinforcing material, the length of the fibers, and the volume fraction of the reinforcing material.
Short fibers are less effective than long fibers.
Bond strength between fibers and matrix is a critical to avoid fiber pullout and delamination, and to maintain good load transmission.
(mostly short or long fibers, not continuous)
Orthogonal (20-40%) Unidirectional (100%)
Book ‘Des Materiaux’, Jean-Paul Baïlon, Edition Polytechnique.