1、PHYSICO-CHEMICAL PROPERTIES OF NYLONS,L. Costa e P. Bracco University of Torino,. Which is its chemical structure? . How long is it? . How polymeric chains are organised in the rope? . How do mechanical properties vary? . Why polymers can degrade?,How a polymer chain is structured?,Chemical structur
2、e:,Nylon 6 o PA-6,Poly(caprolactam),amino caproic acid,Caprolactam,Chemical structure:,Nylon 6,6 o PA-66,Hexamethylene diamine + Adipic acid,Chemical structure:,Nylon 6,Nylon 6,6,Same C/H/N/O ratio, but different structures: they are different materials with different physico-chemical and mechanical
3、 properties,Can we define a scale model?,How long a nylon chain is?,Two definitions:,n = polymerisation degree (number of monomeric units into a polymer chain).,For nylon fibres ca. 150 units,Molecular mass,Rope: 10,5 mm, length 7-8 m.,Crystalline phase,Amorphous phase,Melting temperature of the cry
4、stalline phase: Nylon 6 225C Nylon 6,6 265C,Crystalline phase,Which are the differences between crystalline and amorphous phases?,Nylon 6 crystal obtained from a 1-4 butanediol solution,Nylon 6 crystal form,Nylon 6,6 crystal form,Which percent of nylon is crystalline phase and which amorphous phase?
5、,50% of crystalline phase,Fibres are obtained by drawing.,The chains are oriented.,At the crystallisation temperature, only part of the polymer chains will organise into crystalline structures, while some will remain in the molten state, below the melting temperature, with a high mobility. A further
6、 temperature decrease, will drive to a temperature in which the chains will tie as in the solid state.,What happens during molten nylon cooling?,Glasses (Polystyrene): Tg 100C,Rubber: Tg -40C,Bottle (LDPE): Tg -70C,The transition temperature between the rubbery liquid state and the glassy solid stat
7、e is named glass transition temperature (Tg) At this temperature the mechanical properties of the polymers undergo dramatic changes,Dry: Nylon 6 circa 60C Nylon 6,6 circa 80C decreasing in humid atmosphere.,Which is the Tg of nylons?,In the amorphous phase the chains are more spaced and small molecu
8、les (i.e. water, oxygen) can penetrate into the polymer, moving through the voids (diffusion process).,Any other difference between amorphous and crystalline phase?,Thus, can the physico-chemical and mechanical properties of polymers decay upon time?,YES,Do polymers degrade upon time?,The most relev
9、ant degradation is a decrease of the polymerisation degree,If the original polymerisation degree was 150, 2 bond scissions will give chains of 50 units.,Photo-oxidative degradation: the combined effects of light and oxygen can lead to chain scissions.,Two main processes:,Hydrolytic degradation: due
10、to the action of water. Can be excluded in the conditions of use of a rope.,The UV radiation (especially with wavelengths below 290 nm) has enough energy for breaking bonds omolitically, giving very reactive radicals.,The radicals react with oxygen starting a cyclic process.,Nylon Plastics Handbook ed. Melvin L. Kohan Hanser Publishers Munich,If you wish to know more about the polymers, try polymers on the web:,http:/www.psrc.usm.edu/macrog/index.htm,http:/www.polial.polito.it/cdc,Reference:,Thank you,
