Title Mehanička svojstva polimera Title (english) Mechanical properties of polymers Author Ivona Dolčić Mentor Sanja Lučić Blagojević (mentor)Committee member Sanja Lučić Blagojević (predsjednik povjerenstva)Committee member Zrinka Buhin Šturlić (član povjerenstva)Committee member Domagoj Vrsaljko (član povjerenstva)Granter University of Zagreb Defense date and country 2015-09-11, Croatia Scientific / art field, TECHNICAL SCIENCES Abstract Pri uporabi polimera potrebno je poznavati njihova mehanička svojstva. Mehanička svojstva polimera izravno ovise o njihovoj molekularnoj strukturi. U ovom radu ispitana su mehanička svojstva polistirena (PS), polistirena visoke udarne žilavosti (HIPS), polietilena niske gustoće (PE-LD), polietilena visoke gustoće (PE-HD), polikaprolaktona (PCL), polilaktida (PLA) i poliuretana (PUR) i povezana su s njihovom strukturom. Rastezna svojstva ispitana su testom jednoosnog naprezanja, a relaksacijska svojstva testom relaksacije naprezanja. Uzorci su pripravljeni na hidrauličkoj preši, a testovi su provedeni na univerzalnoj mehaničkoj kidalici.
Mehanička svojstva povezana su s nekoliko važnih strukturnih čimbenika polimera. Ovise značajno o temperaturi staklišta, odnosno o stanju u kojem se nalaze polimer pri temperaturi mjerenja. Tako PS i PLA koji imaju staklište iznad temperature mjerenja imaju vrlo veliki modul elastičnosti i naprezanje, a malo istezanje prije loma, što proizlazi iz činjenice da se na temperaturi mjerenja nalaze u staklastom stanju u kojem su molekule vrlo krute te bez deformacije podnose visoko naprezanje. Za razliku od njih PE i PCL su u viskoelastičnom stanju u kojem su makromolekule vrlo gibljive pa imaju manje module i manje naprezanje te veće istezanje prije loma.
Drugi važan čimbenik je stupanj kristalnosti. PE-HD koji ima znatno veći stupanj kristalnosti od PE-LD-a puno je krtiji, ima i mnogo veći modul, veće naprezanje i puno manje istezanje prije loma, te za razliku od PE-LD-a, nema točku popuštanja.
Treći važan čimbenik je dodatak neke druge faze, primjerice elastomernog polibutadiena u polistiren. Dodatak polibutadiena u polistiren snižava vrijednost modula i prekidno naprezanje te višestruko povećava prekidno istezanje jer polibutadien apsorbira energiju i omogućava elastično istezanje.
Osim navedenih utjecaja, važna je također i kopolimerna stuktura kao kod poliuretana. Poliuretan je izgrađen od dvije faze: tvrde kristalne, koja ima staklište ispod mjerne temperature i meke amorfne koja ima staklište ispod sobne. Meka faza koja je već pri malim naprezanjima podložna trajnoj deformaciji određuje nisku vrijednost modula, ali i omogućava veliko, reverzibilno istezanje jer se pod utjecajem vanjske sile orijentiraju u smjeru istezanja dok tvrda faza sprječava nastanak mikropukotina i tako povećava čvrstoću i žilavost PUR-a.
Abstract (english) When using polymers, it is crucial to know their mechanical properties. Mechanical properties of polymers directly depend on their molecular structure. In this thesis the mechanical properties of the following polymers were tested and related to their structure: polystyrene (PS), high impact polystyrene (HIPS), high density polyethylene (PE-HD), low density polyethylene (PE-LD), polycaprolactone (PCL), polylactide (PLA) and polyurethane (PUR). Mechanical properties that were tested are tensile and relaxation properties. Tensile properties were tested with a uniaxial stress test and relaxation properties with a stress relaxation test. The samples were made on a hydraulic press and tested on a universal mechanical testing machine.
Mechanical properties are related to a several important structural factors. They depend on the glass transition temperature, i.e. on the state of the polymer at the measuring temperature. PS and PLA, which have the glass transition temperature higher than the measuring temperature, have a high elasticity modulus and stress, and a low strain se break, which comes from the fact that they are in the glassy state in which the molecules are very rigid and they can endure high stress without deformation. Unlike them, PE and PCL are in the viscoelastic state in which the macromolecules are very flexible so they have lower elasticity modules and stress, and higher strain at break.
The second important factor is the level of crystallinity. PE-HD, which has a higher level of crystallinity than PE-LD, is more brittle, has a higher elasticity module and stress, and a much lower strain before fracture. Unlike PE-LD, it does not have a yield point.
The third factor is the addition of another phase, e.g. elastomeric polybutadiene in polystyrene. Adding polybutadiene lowers the elasticity module and fracture stress and increases the fracture strain because polybutadiene absorbs energy and allows elastic strain.
The copolymer structure is also important, like in polyurethane. Polyurethane has two phases: hard crystalline phase, which has the glass transition temperature higher than the measuring temperature and soft amorphous phase which has the glass transition temperature lower than the measuring temperature. The soft phase allowes high, reversible strain and the hard phase stops the formation of microcracks and increases hardness and toughness.
Keywords
mehanička svojstva
PS
HIPS
PE-LD
PE-HD
PCL
PLA
PUR
temperatura staklišta
stupanj kristalnosti
Keywords (english)
mechanical properties
PS
HIPS
PE-LD
PE-HD
PCL
PLA
PUR
glass transition temperature
level of crystallinity
Language croatian URN:NBN urn:nbn:hr:149:759686 Study programme Title: Chemical Engineering - Undergraduate study Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2016-11-22 09:25:54
