Structure and the physical and mechanical properties of dental hybrid composite materials

Abstract

Kompoziti sa dodatkom nanočestica pokazuju poboljšanje mehaničkih svojstava. PMMA polimer korišćen je kao matrica u kombinaciji sa dva različita ojačanja, koja imaju izrazito različite oblike, kada su dodati u kompozit. Ojačanja napravljena od aluminijum oksidnih čestica imaju sferičan oblik a viskersi imaju odnos dužina prema prečniku od 200. Uticaj veličine čestica, njihov oblik i udeo, na mehanička svojstva proučavani su pomoću nanoindentacionih merenja i dinamičko-mehaničke analize. Utvrdjeno je da i ćestice i viskersi poboljšavaju mehanićka svojstva, ali poboljšanje je mnogo više izraženo u slučaju viskersa. Koncentracija ojačavajućih čestica varira do 5 mas. %. Najbolja svojstva dobijena su sa dodatkom 3 mas. % viskersa u pogledu mehaničkih svojstava dobijenog kompozita. U disertaciji su prikazani rezultati istraživanja uticaja procesnih parametara elektropredenja na uniformnost, morfologiju i sastav nanokompozitnih vlakana u obliku mata (PVB/Sep). Suspenzija sepiolita ima tiksotropna svojstva zbog svoje vlaknaste prirode, velike specifićne površine i prisustva silanolnih grupa na površini. Funkcionalizacija sepiolitnih vlakana uradjena je u vodenom tiksotropnom gel stanju korišćenjem silana kao vezivnog agensa. Ispitano je ponašanje pri elektropredenju suspenzije tri različite koncentracije sepiolita (3 mas. %, 30 mas. % i 59 mas. %) u rastvoru PVB u etanolu sa i bez modifikacije silanima vlakana sepiolita. Utvrdjeno je da pod istim uslovima kompozitna vlakna PVB/Sep imaju nižu vrednost srednjeg prečnika vlakana nego čista PVB vlakna. Optimalni uslovi dobijanja najravnomernijih nanokompozitnih vlakana se postižu pri protoku suspenzije od 0,5 mL/h, rastojanju dizne od kolektora 15 cm i naponu od 24 kV.

Composites with the addition of alumina nanofillers show improvement in mechanical properties. The PMMA polymer was used as a matrix and two different types of nanofillers, added as reinforcement in the matrix, having extremely different shapes were added to form the composite. Reinforcements were made of alumina spherical nanoparticles having spherical shape and whiskers having the length to diameter ratio of 200. The influence of alumina fillers size, shape and fillers loading on mechanical properties of obtained composite were studied using the nanoindentation measurements and dynamic mechanical analysis. It was observed that both alumina whiskers and alumina spherical nanoparticles added in the PMMA matrix improved the mechanical properties of obtained composite samples but the improvement was significantly higher with alumina whisker reinforcement. The concentration of the reinforcing alumina spherical nanoparticles and alumina whiskers in PMMA matrix varied up to 5 wt. %. The best performance was obtained by the addition of 3 wt. % of alumina whiskers in the PMMA matrix with regard to mechanical properties of the obtained composite. This study presents investigation of processing conditions on the uniformity, morphology and structure of patterned nanofibrous mats for poly (vinyl butyral)/sepiolite (PVB/Sep) nanocomposite fibers obtained by electrospinning process. Sepiolite aqueous suspensions show a thixotropic behavior because of their fibrous structure, porosity, large specific surface area and the presence of silanol groups on the surface. Functionalization of the sepiolite fibers in aqueous thixotropic gel was made on the surface of individual fibers using amino silanes as coupling agents. Different contents (3 wt. %, 30 wt. % and 50 wt. %) of neat and modified sepiolite fibers were dispersed by ultrasonic irradiation in the solution of PVB in ethanol and were used to obtain nanocomposite fibers by electrospinning. The PVB/Sep nanocomposite fibers showed lower mean fiber diameter than of the neat PVB fibers. Uniform nanofibers 8 were obtained using the lower flow rate (0.5 mL/h), high collector distance (15 cm) and a constant applied voltage of 24 kV.