Influence of alumina particles on the mechanical and thermal properties of acrylate composite materials

Biokompatibilni materijali su materijali koji se primenjuju u kontaktu sa ćelijama, tkivima ili telesnim tečnostima ljudskog organizma kako bi se nadomestila oštećenja do kojih dolazi usled starenja, bolesti ili nesrećnih slučajeva. Ovi materijali se koriste za izradu medicinskih implantata i kao takvi moraju ispuniti određene kriterijume u pogledu biokompatibilnosti, izdržljivosti, velike otpornosti prema koroziji, netoksičnosti, čvrstoći, žilavosti i trajnosti. Ujedno, njihov cilj je da ostanu funkcionalni i što je duže moguće u organizmu čoveka. Pod dentalnim materijalima se podrazumevaju oni materijali koji se koriste u različitim stomatološkim zahvatima, bilo za stalnu ili privremenu primenu oralne potrebe pacijenata. Zbog te činjenice oni imaju strogo definisane zahteve, u vezi sa njihovim ponašanjem u uslovima eksploatacije. Poli (metil metakrilat), PMMA, ima široku primenu u protetici i predstavlja jedan od često korišćenih materijala. Pošto se koristi kao dentalni proizvod, on mora ispuniti određene zahteve u vezi sa ponašanjem u uslovima njegove eksploatacije. Poboljšanje njegovih mehaničkih svojstava, dodavanjem ojačanja u vidu aluminijum-oksida je od velikog značaja za dalja istraživanja u ovoj oblasti. Radi poboljšanja mehaničkih i termičkih svojstava kompozitnih materijala na bazi akrilata, u okviru ove doktorske disertacije urađena je modifikacija polaznog materijala, dodavanjem ojačanja u vidu čestica aluminijum-oksida dopiranih sa 3-aminopropil-trimetoksilanom (AM) i metil estara zasićenih masnih kiselina lanenog ulja (biodizel-BD). Kao matrica je korišćen komercijalni PMMA sa dodatkom dimetil itakonata (DMI), dok su modifikovane čestice aluminijum oksida korišćene kao ojačanje. Modifikacija čestica je izvedena u dva koraka: dodatkom 3-aminopropil-trimetoksilana (AM) i metil estra masnih kiselina lanenog ulja (BD). Matrica polimera služila je kao reper radi poređenja sa pripremljenim kompozitima koji su imali po 1 wt. %, 3 wt. % i 5 wt. % modifikovanih čestica Al 2 O3 - AM i Al 2 O3 -BD. Predmet i cilj ove doktorske disertacije je bio da se eksperimentalno utvrde mogućnosti poboljšanja strukture matrice ovom modifikacijom kao i da se da doprinos poznavanju uticaja ojačanja u vidu aluminijum oksida na mehanička i termička svojstva kompozitnog materijala. Na novodobijenom materijalu su izvedena mehanička i termička ispitivanja, kao i mikrostrukturna karakterizacija. Na osnovu dobijenih rezultatata strukturnih, morfoloških, termičkih i mehaničkih analiza je ustanovljeno da dobijeni uzorci kompozitnog materijala imaju potencijal sa širom primenom. Takođe, cilj je bio i da se utvrdi uticaj različitih doza gama zračenja na mehanička i termička svojsta, mikrobiološku čistoću kompozitnog materijala, kao i promenu mikrostrukture i boje. Dobijeni rezultati su ukazali da je novo dobijeni materijal kvalitetniji i sa poboljšanim mehaničkim svojstvima, a istraživanja na prelomnim površinama su pokazala da je dodavanjem ojačanja moguće dobiti finiju i homogeniju mikrostrukturu što nedvosmisleno utiče i na dobijena mehanička svojstva. Doprinos ove doktorke disertacije je primena matematičkog modela – hemometrije tj. veštačke neuronske mreže (ANN model) čime se proveravala mogućnost primene ovog modela u cilju predviđanja mehaničkih i termičkih svojstava materijala.Biocompatible materials are materials that are applied in contact with cells, tissues or body fluids of the human body to compensate for damage caused by aging, disease or accidents. These materials are used to make medical implants and as such must meet certain criteria in terms of biocompatibility, durability, exceptional corrosion resistance, non-toxicity, strength, toughness and durability. At the same time, their goal is to remain functional in the human body for as long as possible. By dental materials we mean those materials that we use in various dental procedures, either for permanent or temporary application in the mouth of patients. Due to this fact, they have special requirements regarding behavior in conditions of exploitation. Poly(methyl methacrylate) (PMMA) is widely used in prosthetics and is one of the commonly used materials in prosthetics. Since it is used as a dental material, it must meet certain requirements regarding the behavior in the conditions of its exploitation. Improving the mechanical properties by adding reinforcement in the form of aluminum oxide is of great importance for further research in this field. It has been proven that the mechanical properties are significantly improved by adding very small amounts of these particles to the material. Within this doctoral dissertation, the mechanical ans thermal properties of acrylate-based composites were investigated. To improve the mechanical and thermal properties of acrylate-based composites, tests were performed by adding reinforcements in the form of alumina particles doped with 3-aminopropyl trimethoxylan (AM) and methyl esters of saturated fatty acids of flaxseed oil (biodiesel-BD). Commercial poly (methyl methacrylate) (PMMA) with the addition of dimethyl itaconate (DMI) was used as a matrix, while modified alumina particles were used as reinforcement. Particle modification was performed in two steps: by the addition of 3-aminopropyl-trimethoxylan (AM) and flaxseed oil (BD) fatty acid methyl ester. After that, the polymer matrix was compared with the prepared composites that had 1 wt. %, 3 wt. % and 5 wt. % of modified Al2 O3 -AM and Al 2 O3 -BD particles. The aim of this dissertation was to contribute to the knowlendge of influence of aluminium oxide reinforcement on the mechanical and thermal properties of the composite material, and to experimentally determine the possibilities of improving the structure of the matrix with this modification. Mechanical and thermal properties, as as well as microstructural characterization, were tested on the newly obtained material. Based on the obtained results of structural, morphological and thermal analyses, it is established that the composite material samples indicate the potential for wider application. Also, the goal was to determine the influence of different doses of gamma radiation on the newly obtained material. The microbiological purity of the composite material was examined, as well as changes in mechanical and thermal properties along with changes in microstructure and color. The obtained material is of better quality and mechanically more resistant, and the results of the microstructure test showed that by adding reinforcement it is possible to obtain a finer and more homogeneous microstructure, and thus the mechanical properties are improved. Thereafter, mathematical models were applied - hemometrics, that is artificial neural networks (ANN models), in order to determine whether the same models can be used to predict the mechanical and thermal properties of materials

The use of coated micropowders to reduce radiation heat transfer in foam insulation

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1991.Includes bibliographical references (leaves 126-129).Polyurethane foam is the most effective insulation currently available for buildings. Chlorofluorocarbon (CFC) blowing agents, which have low thermal conductivities, contribute highly to the effectiveness of this insulation. However, CFC blowing agents are being phased out because they are depleting the earth's protective ozone layer. Alternate blowing agents, with higher thermal conductivities, will compromise the insulating value of the foam insulation. To counteract this effect, the author has sought to improve the effectiveness of foam insulation by increasing its extinction coefficient. In this work, theoretical analysis and experimental measurements have been used to study and increase the extinction coefficient of polyurethane foam insulation. Radiative heat transfer, which accounts for approximately 25% of the total heat transfer through foams, is inversely proportionate to the extinction coefficient. Foam cell walls presently have a transmissivity of about 80% to infrared radiation. The extinction coefficient of foams can be improved by decreasing the cell sizes or by increasing the absorptivity of the foam cell walls. The approach of this work has been to increase the cell wall opacity through the addition of opaque micropowders. Conduction through the solid polymer is of the same magnitude as the radiative transfer, also accounting for approximately 25% of the heat transfer of the foam. To maintain the low thermal conductivity of the polymer, the micropowders added to reduce radiative transfer through the foam must not change its characteristic conductivity. Polymer micropowders with thermally opaque coatings of graphite have been developed in this work using core micropowders with diameters between 8 and 30 [mu]m. Theory predicts that the smaller the particle size, the larger the resulting improvement in extinction coefficient. The coatings required for opacity are less than 0.1 [mu]m thick, composing less than 7% of the overall volume of the powder. The extinction coefficients of the coated micropowders have been experimentally derived and agree well with analytical predictions. These coated micropowders have been added to foams with the goal of increasing their extinction coefficients. The resulting foams indeed demonstrate improved extinction coefficients when compared to a powderless control foam. This improvement results both from reduction in cell size and increased cell wall opacity. The resulting effective conductivities of the foams have been decreased by as much as 6% through the addition of these relatively large micropowders. These results correlate well with predicted values and indicate that the addition of smaller particles will result in even more improvement.by Arlene Lanciani Marge.M.S