Synthetic Condensation polymers: Dacron & Nylon 6AS Group 3 Kitty Au-Yeung Giselle Ho Rachel Chui Cici Tam Angela Tsui

Positive impacts of development of polymers on our society Plastics have replaced an increasing number of natural substances Synthetic textile fibers have revolutionized the textile industry the low cost, light weight, strength and design adaptability of plastics meet a variety of applications Nylon replaced silk in military applications such as parachute and flak vests, and was used in many types of vehicle tires A synthetic fiber manufacturing facility occupies a much smaller area of ground than would be needed to produce an equal quantity of natural fibers, such as cotton, wool or silk.

Negative impacts of development of polymers on our society Birds may eat the plastic scraps mistakenly and die Fishing gear tangles up to form a net and kill sea creatures

Negative impacts of development of polymers on our society Various nylons break down in fire and form hazardous smoke, and toxic fumes or ash, containing hydrogen cyanide Some plastic contains toxic chemicals such as Phthalates which cause reproductive disorders Some polymers are non-biodegradable and become solid waste which occupy many spaces in the landfill

The effect of structures on the properties of nylon

Hardness and rigidity able to crystallize mostly because of strong intermolecular hydrogen bonds through the amide groups and because of Van der waal’s forces between the methylene chains Crystallinity of nylons can be controlled by nucleation, i.e., seeding the molten polymer to produce uniform sized smaller spherulites

Hardness and rigidity Increase with crystallinity Reason for high crystallinity: 1. Polar planar amide (-CO-NH-) groups result in multiple hydrogen bonds among adjacent strands of nylon 2. Nylon backbone is regular and symmetrical

Crystal structure of nylon 6 and nylon 6.6

Hardness and rigidity Nylon 6.6: Have multiple parallel strands aligned with their neighbouring peptide bonds at coordinated separations the chains have no directionality Carbonyl oxygens and amide hydrogens form interchain hydrogen bonds repeatedly

Hardness and rigidity Nylon 5,10: Have coordinated runs on 5 and 8 carbons Parallel strands participate in an extended, unbroken, strong and tough super- molecular structure Nylon 6: Form uninterrupted hydrogen-bonded sheets with mixed directionalities adjacent chains are anti-parallel and the hydrogen bonding is between adjacent chains within the same sheet (bisecting the CH 2 angles the chains are parallel and the hydrogen bonding is between chains in adjacent sheets

Hardness and rigidity When extruded into fibres… Individual polymer chains align because of viscous flow Fibres align further in the cold drawing afterwards Crystallinity is increased and hence hardness as well as rigidity

Hydrolysis and degradability All nylons are susceptible to hydrolysis(Strong acids and water at high temperatures) Lower members of the nylons (such as nylon 6) are affected more than higher members (such as nylon 12) Cannot be used in contact with sulphuric acid for example, such as the electrolyte used in lead-acid batteries Must be dried to prevent hydrolysis in the moulding machine barrel By adding heat stabilizer can allow usage at elevated temperature for long-term performance By adding carbon black can reduce the radiation degradation

Tensile strength The strength of nylon comes from amide groups in its molecular chain A very regular shape Well suited to create fabrics designed to stand up to intense forces Ultra drawing of solidified crystalline material induces a high degree of chain extension, which leads to very high tensile strength Major material used in parachutes and ropes during the Second World War Bullet-proof vests and other hard wearing items now

Model of extended molecule chain in superdrawing fibre

The End