Polymers and Ceramics Team 6: Christopher Chavez Steve De La Torre David Jaw Matthew Witkowski September 21, 2005 ME260L Topics: Polymers (S. De La Torre) Additives and Properties (M. Witkowski) Glass and it Properties (D. Jaw)
Related searches for Biodegradable Plastics
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Steve De La Torre
September 21, 2005
STRESSHow does one know if a material will be strong enough for a part?
If the loads can be predicted and the part shape is known then the designer can estimate the worst load per unit of cross-sectional area within the part. Load per unit area is called "STRESS".
If Force or Load is in pounds and area is in square inches then the units for stress are pounds per square inch
Biodegradable- means that microbial species in the environment will degrade a portion (or all) of polymeric material, under the proper environmental conditions, and without producing toxic by-products.
3 Biodegradable Plastics
1. starch-based system: farthest along in production capacity
2. lactic-based system: based in medical and pharmaceutical uses
3. fermentation of sugar: process results in production of a highly crystalline and very stiff polymer (acts similar to polymers from petroleum)
Recycling Symbols are used to correspond with each plastic:
1. PETE (polyethylene)
2. HDPE (high-density polyethylene)
3. V (vinyl)
4. LDPE (low-density polyethylene)
5. PP (polypropylene)
6. PS (polystyrene)
Rubber- defined as being capable of recovering from deformations quickly
-Natural rubber: latex base (milk-like sap from inner bark of tropical tree), resistance to fatigue and abrasion
-Synthetic rubbers: better resistance to heat, chemicals, and gasoline than natural rubber.
-Silicones: most useful range of temperature of elastomers, low resistance to oil and wear
-Polyurethane: high strength, as well as harness and stiffness, good resistance to breaking and abrasion
Raw Materials- clay (oldest, fine-grained sheet-like structure), kaolinite (white clay made of silicate of aluminum, slippery and moldable characteristics), flint (composed of fine silica), feldspar (crystalline minerals with aluminum silicates and potassium, sodium, or calcium)
Porcelain- white ceramic made of kaoline, quartz, and feldspar
Cermets: made up of oxides, nitrides, and carbides
Silica: a polymorphic material, high-temperature resistanc
Nanoceramics and composites
nanophase ceramics: consist of atomic clusters containing thousands of atoms
second-phase particles: used as reinforcements in composites (have tensile strength and creep resistance)
The tensile strength increases with decrease in grain size and porosity
UTS= UTSoe-nPP= volume fraction of pores in the solid
The Modulus of elasticity of ceramics is related to the porosity
E= Eo( 1- 1.9P+ 0.9P2) Eo= the modulus at zero porosity
Ceramics are have less thermal-shock tolerance and impact toughness than metals and thermoplastics. This is due to their lack of ductility. Ceramics have static fatigue caused by cyclic loading. Methods to pre-stress ceramics are:
Thermal conductivity ranges and is related to porosity
k= ko (1- P)
Thermal cracking- when a small piece or layer breaks off, tends to be lower with a combination of low thermal expansion and high thermal conductivity
Anisotropy of thermal expansion- when thermal expansion ranges with different directions through the ceramic, causes thermal stresses that lead to cracking
Bioceramics- used as biomaterials for human joints because of strength and inertness, they create a structurally strong bond
molecular arrangement in a crystal
molecular arrangement in a glass
Highest stiffness and strength are achieved when fibers are aligned with tension force.
Unidirectional strongest, weaker transverse properties.
Optimal configuration for specific task.
Weaving techniques for optimal strength