Ayse Aytac

Effects of initial fiber length and fiber length distribution on the properties of carbon-fiber-reinforced-polypropylene composites

In this study, short carbon fiber-reinforced polypropylene composites with three different initial carbon fiber lengths were prepared by using extrusion compounding and injection molding techniques. The physical and morphological properties of the prepared short carbon fiber-reinforced composites were investigated by means of tensile test, differential scanning calorimetry and scanning electron microscopy. Final fiber length distributions of composites were also determined by using an image analyzing program. It was found that the maximum number of fibers was observed in the range from 51 to 100 µm. Number average final fiber lengths were calculated between 230 and 280 µm. Regardless of the used initial carbon fiber length, tensile strength and modulus values of the composites increased with the increasing carbon fiber content. It has been concluded that the initial fiber length at the studied range did not have any significant effect on the properties of composites.

Properties of alkali treated short flax fiber reinforced poly(lactic acid)/polycarbonate composites

The main focus of this study is to investigate the properties of alkali treated flax fiber reinforced poly(lactic acid)/polycarbonate (PLA/PC) composites. Characterization of these composites was performed by conducting tensile strength, dynamic mechanical analysis (DMA), differential scanning calorimeter (DSC) and scanning electron microscope (SEM) analyses. Tensile strength results revealed that the highest mechanical performance was observed for 2 % sodium hydroxide (NaOH) treated flax fiber reinforced PLA/PC composites. DMA analysis also supported the results of the tensile tests. Tan delta (δ) curves were used for evaluating the fiber-matrix adhesion in flax fiber reinforced composites. The lowest peak magnitude and consequently the best fiber-matrix adhesion were also observed for 2 % NaOH treated flax fiber reinforced composites. DSC results showed that slight changes occurred in glass transition and melting temperature values. Moreover, crystallinity of PLA was affected by the flax fiber reinforcement. The maximum crystallinity value was observed in 2 % NaOH treated flax fiber reinforced composites. Furthermore, SEM analysis showed that 2 % NaOH treated flax fibers have better interfacial bonding with PLA/PC matrix among the flax fibers.

Properties of modified ethylene terpolymer/poly(lactic acid) blends based films

In order to explore an alternative method instead of plasticization for improving the toughness, flexibility and processability of PLA based packaging films, two different kinds of modified polyethylene based elastomers, such as glycidyl methacrylate or maleic anhydride functionalized ethylene-acrylate based elastomers, were melt blended with PLA. Their properties were compared with conventional PEG plasticized PLA. The chemical interaction between end groups of PLA and epoxide or maleic anhydride functional groups of elastomers was shown by FTIR. Scanning electron microscopy showed that up to 20 % PEG loading, one phase morphology was achieved, however beyond this point, a phase separation was observed for plasticized PLA. For PLA/elastomer blends, a two-phase morphology was obtained as a result of immiscible nature of PLA and elastomers. Tensile and dynamic mechanical properties indicated that elastomer based blends were better than plasticized PLA independently from elastomer type. Differential scanning calorimeter (DSC) analysis exhibited that the Tg value was remarkably lowered in the plasticized PLA; however, it did not change in the case of elastomers. In terms of oxygen permeability and biodegradability, plasticized PLA was found to be better than elastomer based blends.

FATIGUE PROPERTIES OF NYLON 66/POLYESTER HYBRID CORDS

Abstract In this study, the fatigue and mechanical properties of Nylon 66/Polyester (Ny 66/PET) hybrid cords and Ny 66 and polyester reference cords which are being used in tire industry were studied. The most effective parameters and the optimum twist levels were determined for the fatigue performance of Ny 66/PET hybrid cords. Taguchi design of experiment method is used to minimize the required number of experiments. Different sets of nylon and PET reference cords were prepared in order to make a comparison of fatigue performance. The selected process parameters for Taguchi experimental analysis were Ny 66, PET, and cable ply twist levels. The effects of the selected parameters were investigated. It was found that the most effective factor was cable twist level and better fatigue resistance for hybrid cords with high cable and PET ply twist level can be obtained.

Influence of different surface-coated carbon fibers on the properties of the poly(phenylene sulfide) composites

This paper aims to study the effect of different surface coatings of carbon fiber on the thermal, mechanical, and morphological properties of carbon fiber reinforced poly(phenylene sulfide) composites. To this end, unsized and different surface-coated carbon fibers were used. Prepared poly(phenylene sulfide)/carbon fiber composites were characterized by using Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, tensile test, dynamic mechanical analysis, and scanning electron microscopy. Tensile strength values of the surfaced-coated carbon fibers reinforced poly(phenylene sulfide) composites are higher than the unsized carbon fiber reinforced poly(phenylene sulfide) composite. The highest tensile strength and modulus values were observed for the polyurethane-coated carbon fiber reinforcement. Dynamic mechanical analysis studies indicated that polyurethane-coated carbon fiber reinforced composite exhibited higher storage modulus and better adhesion than the others. Differential scanning calorimetry results show that melting and glass transition temperature of the composites did not change significantly. Scanning electron microscopic studies showed that polyurethane and epoxy-coated carbon fibers exhibited better adhesion with poly(phenylene sulfide).

Alev geciktiricilik özelliği geliştirilmiş ve plastikleştirilmiş poli(laktik asit)’in özelliklerine farklı nano katkıların etkisinin incelenmesi

Bu calismada, trifenil fosfat ile yanmazlik ozelligi gelistirilmis ve plastiklestirilmis poli(laktik asit)’in ozellikleri uzerine farkli nano katkilarin etkisi incelenmistir. Bunun icin oncelikle plastiklestirilmis ve trifenil fosfat eklenmis poli(laktik asit) kompoziti kontrol numunesi olarak uretilmistir. Bu kompozite uc farkli oranda nanokil, karbon nanotup ve amino propil izobutil poli(hedral oligomerik silseski okzan), alev geciktirici miktari azaltilarak eklenmistir. Ornekler, ekstruderde eriyikten karistirma ve enjeksiyon kaliplama yontemleri ile hazirlanmistir. Elde edilen orneklerin isil, mekanik, yanmazlik ve morfolojik ozellikleri incelenmistir. Cekme testine gore %1 amino propil izobutil poli(hedral oligomerik silseski okzan) iceren nanokompozit en yuksek cekme dayanimi ve kopma uzamasi degerini gostermistir. Karbon nanotup ve amino propil izobutil poli(hedral oligomerik silseski okzan) kullanildigi durumda, artan yukleme miktarina bagli olarak kopma uzamasi ve cekme dayanimi degerleri dusmustur. Termogravimetrik analiz sonuclarina gore tum nanokompozitlerin bozunma sicakliklarinin uretim sicakligindan yuksek oldugu gorulmustur. Taramali elektron mikroskobu analizinde, trifenil fosfat, nanokil ve karbon nanotup icerikli kompozitlerde homojen bir dagilim gozlenmistir. Gecirimli elektron mikroskobu analizi bu sonucu desteklerken, amino propil izobutil poli(hedral oligomerik silseski okzan) icerikli nanokompozitde nanoboyutta agregalar gozlenmistir. Yapilan sinirlayici oksijen indeksi testi sonucunda en iyi deger nanokil icerikli kompozitlerde elde edilmistir. Dikey yanma testinin sonuclarina gore ise %1-2 nanokil iceren kompozitler V-0 sinifi ile en iyi yanmazlik ozelligi sergilemistir.

Compatibilization of poly(lactic acid)/polycarbonate blends by different coupling agents

In this study, PLA/PC blends were prepared in order to investigate the effects of the addition of PC loading level into PLA matrix on the mechanical properties of these blends. After that, PLA/PC (70/30), which has the lowest tensile strength value, was selected as a control sample for the compatibilization study. Commercial styrene-acrylic multi-functional-epoxide oligomeric agent (SAmfE), styrene maleic anhydride copolymer (SMA), tetrasilanol phenyl polyhedral oligomeric silsesquioxane (T-POSS) and glycidyl isooctyl-polyhedral oligomeric silsesquioxane (G-POSS) were used as compatibilizers for PLA/PC blends. The variation of mechanical, thermal, structural and morphological properties were examined by conducting tensile tests, dynamic mechanical analyses, differential scanning calorimetry, Fourier Transform IR and scanning electron microscope analyses. Tensile test results showed that the tensile strength and elongation at break values of the PLA/PC blend compatibilized with SAmfE were higher than those of the other blends. DSC analyses revealed that Tg and Tm values of the blends were not significantly affected by compatibilizer but, degree of crystallinity was found to be sensitive to compatibilizer type. DMA results showed that the best mechanical properties were obtained for the PLA/PC/SAmfE blend. When all of the results evaluated, it was found that the SAmfE is the most effective compatibilizer among the using compatibilizer types for PLA/PC blends.

Improving the properties of recycled PET/PEN blends by using different chain extenders

Abstract The main aim of this study was to improve the mechanical properties of the recycled poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) (r-PET/PEN) blends by enhancing the miscibility between PET and PEN with the usage of chain extenders. This idea was novel for the recycled PET-based r-PET/PEN blends, as investigation of the effects of the chain extender usage on the properties of r-PET/PEN blends has not been studied in the literature, according to our knowledge. 1,4-Phenylene-bis-oxazoline (PBO), 1,4-phenylene-di-isocyanate (PDI), and triphenyl phosphite (TPP) were selected as chain extenders. The maximum tensile strength value was observed for the 1.0PDI sample. Moreover, PDI-based blends exhibited better Izod impact strength when compared with all other samples. The miscibility and degree of crystallinity values of all blends were discussed by means of thermal analysis. 1H-nuclear magnetic resonance (1H-NMR) analysis was carried out to determine transesterification reaction levels. According to 1H-NMR results, the increase in the level of transesterification was around 40% with the usage of PDI. The optimum loading level for selected chain extenders was determined as 1 wt.%, and PDI-based blends exhibited better properties when compared with those of the blends based on PBO and TPP at this loading level.