polymer and glass

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Polymer and GLASS BY Mr.Aashis.S.Roy Materials Science Gulbarga University Gulbarga-585106

Polymer Chemistry : 

Polymer Chemistry Part 1 Polymer Characteristics and Classifications

Definitions : 

Definitions Polymer – A very long molecule composed of repeating units connected by covalent bonds Monomer – A repeated unit in a polymer. The reactant for the polymerization reaction.

Characterizing a Polymer : 

Characterizing a Polymer Structure Classification Synthesis

Structure of a Polymer : 

Structure of a Polymer Skeletal Structure Chemical Structure

Skeletal Structure : 

Skeletal Structure Linear – a chain with two ends

Skeletal Structure : 

Skeletal Structure Branched – have side chains

Skeletal Structure : 

Skeletal Structure Crosslinked (Networked) – chains are connected to other chains

Chemical Structure : 

Chemical Structure Homopolymer – only one monomer (repeating unit) - A – A – A – A – A – A – A - Copolymer – more than one monomer

Copolymers : 

Copolymers Alternating - A – B – A – B – A – B – A – B - - A – A – B – B – A – A – B – B - Block -A-A-A-A-A-B-B-B-B-B-A-A-A-A-A- -A-A-A-A-A-A-A-B-B-B-B-B-B-B-

Copolymers : 

Copolymers Graft B-B-B-B-B-B-B B -A-A-A-A-A-A-A-A-A-A-A-A-A-A-A- B B-B-B-B-B-B

Classifications : 

Classifications Thermoplastic Elastomer Thermoset

Thermoplastics : 

Thermoplastics Linear or branched polymers which can be melted when heat is applied. Can be molded into any shape with processing techniques such as injection molding or extrusion. Most common “plastics”

Thermoplastics : 

Thermoplastics Plastics – bottles, grocery bags, water piping, rope, fishing line, car parts Most are recyclable Natural thermoplastics – silk, cellulose (proteins), polylactic acid

Codes for Plastics : 

Codes for Plastics 1 – PETE – soft drink bottles 2 – LDPE – plastic bags, toys 3 – PVC – water pipes 4 – HDPE – milk jugs 5 – PP – bottle caps 6 – PS – styrofoam

Elastomers : 

Elastomers Crosslinked (networked) rubbery polymers that can be stretched easily (3-10x original size) Rapidly recover original dimensions when applied stress is released. Low degree of crosslinking

Elastomers : 

Elastomers Uses – examination gloves, rubber bands, bouncing balls Not recyclable Degrades (burns/scorches) when heat is added Natural elastomers – natural rubber, latex

Thermosets : 

Thermosets Normally are rigid materials. Network polymers in which chain motion is greatly restricted by a high degree of crosslinking. Cannot be reshaped once formed. epoxy

Thermosets : 

Thermosets Uses – high temperature electrical applications, super glue, counter top laminates, epoxy resins, tires (vulcanized rubber) Cannot be recycled (burn/scorch with heat) Natural* thermosets – vulcanized rubber

Polymer Chemistry : 

Polymer Chemistry Part 2 Polymer Synthesis

Polycondensation : 

Polycondensation Reactions in which small molecules (H2O, HCl) are eliminated when the monomers combine.

Polyaddition : 

Polyaddition Reactions in which monomers combine without the elimination of a small molecule. Usually involves the breaking of a double bond.

Polyaddition with Radicals : 

Polyaddition with Radicals Initiation – Creation of an active site (free radical). Propagation – Growth of polymer chain by addition of a monomer to an active site and the creation of a new active site.

Polyaddition with Radicals : 

Polyaddition with Radicals Termination – Growth of chain stops. Combination – Two growing chains collide. Disproportionation – A hydrogen atom is added to the end of a growing chain.

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Glass

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Glass is an amorphous (non-crystalline) solid material. Glasses are typically brittle, and often optically transparent. Glass is commonly used for windows, bottles, and eyewear; examples of glassy materials include soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass, and aluminium oxynitride. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance.

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Glass plays an essential role in science and industry. The optical and physical properties of glass make it suitable for applications such as flat glass, container glass, optics and optoelectronics material, laboratory equipment, thermal insulator (glass wool), reinforcement fiber (glass-reinforced plastic, glass fiber reinforced concrete), and art.

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Glass ingredients Depending on the final use and application the composition of the glass and cooling rate will vary to achieve the adequate properties for the specific application. These are the common ingredients to obtain glass:

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1. Sand (SiO2 silica)In its pure form it exists as a polymer, (SiO2)n. 2. Soda ash (sodium carbonate Na2CO3)Normally SiO2 softens up to 2000°C, where it starts to degrade (at 1713°C most of the molecules can already move freely). Adding soda will lower the melting point to 1000°C making it more

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3. Limestone (calcium carbonate or CaCO3) or dolomite (MgCO3)Also known as lime, calcium carbonate is found naturally as limestone, marble, or chalk.The soda makes the glass water-soluble, soft and not very durable. Therefore lime is added increasing the hardness and chemical durability and providing insolubility of the materials.

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One is sodium carbonate (Na2CO3), which lowers the melting point to about 1500 °C (2700 °F) in soda-lime glass; "soda" refers to the original source of sodium carbonate in the soda ash obtained from certain plants. However, the soda makes the glass water soluble, which is usually undesirable, so lime (calcium oxide (CaO), generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide (Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass. Soda-lime glasses account for about 90% of manufactured glass.

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Most common glass has other ingredients added to change its properties. Lead glass or flint glass, is more 'brilliant' because the increased refractive index causes noticeably more "sparkles", while boron may be added to change the thermal and electrical properties, as in Pyrex. Adding barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eye glasses.

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Main properties of glass These are the main characteristics of glass: Solid and hard material - Disordered and amorphous structure- Fragile and easily breakable into sharp pieces -Transparent to visible light Inert and biologically inactive material. - Glass is 100% recyclable and one of the safest packaging Materials due to its composition and properties Glass is used for architecture application, illumination, electrical transmission, instruments for scientific research, optical instruments, domestic tools and even textiles. Glass does not deteriorate, corrode, stain or fade and therefore is one of the safest packaging materials.

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Types of glass and market application Commercial glass or Soda-lime glass: This is the most common commercial glass and less expensive. The composition of soda-lime glass is normally 60-75% silica, 12-18% soda, and 5-12% lime. A low percentage of other materials can be added for specific properties such as coloring. pure glass SiO2 does not absorb UV light, soda-lime glass does not allow light at a wavelength of lower than 400 nm (UV light) to pass.

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The disadvantages of soda-lime glass is that is not resistant to high temperatures and sudden thermal changes. For example, everybody has experienced a glass breaking down when pouring liquid at high temperature, for example to make tea.

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Lead glass is composed of 54-65% SiO2, 18-38% lead oxide (PbO), 13-15% soda (Na2O) or potash (K2), and various other oxides. When the content of PbO is less than 18% is known as crystal glass. -In high amounts it lowers the melting point and decreases the hardness giving a soft surface; - In addition it has a high refractive index giving high brilliance glass. These two properties make it appropriate for decorating purposes. Glass with high lead oxide contents (i.e. 65%) may be used as radiation shielding glass because lead absorb gamma rays and other forms of harmful radiation, for example, for nuclear industry.

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Borosilicate glass: Borosilicate glass is mainly composed of silica (70-80%), boric oxide B2O3 (7-13%) and smaller amounts of the alkalis (sodium and potassium oxides) such as 4-8% of Na2O and K2O, and 2-7% aluminum oxide (Al2O3). Boron gives greater resistance to thermal changes and chemical corrosion. Boron gives greater resistance to thermal changes and chemical corrosion. It is suitable for industrial chemical process plants, in laboratories, in the pharmaceutical industry, in bulbs for high-powered lamps, etc. Borosilicate glass is also used in the home for cooking plates and other heat-resistant products.

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Chemistry % by Weight of the most common types of glass

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