A R C H I V E S O F M E C H A N I C A L T E C H N O L O G Y A N D A U T O M A T I O N Vol. 33 no. 4 2013 MAREK SZOSTAK MECHANICAL AND THERMAL PROPERTIES OF PET/POSS NANOCOMPOSITES Polyethylene terephtalate PET and polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared by melt mixing. The mechanical and thermal properties of PET/POSS nanocomposites with three different types of POSS (heptaisobuthylotrihydroxy POSS1; octatisdimethylosiloxyethyloepoxy POSS2, and octatisdimethylosiloxy glicydoksypropylo POSS3) and two weight percentage contents (0.2 and 0.5) have been measured. There were no significant changes in the mechanical properties of obtained PET/POSS nanocomposites while the thermal properties changed significantly. DSC study shows big influence of silsesquioxanes type and their percentage content on the crystallization temperature and crystalinity of PET/POSS nanocomposites. The crystallization temperature increased by 5.1 o C for PET/POSS1, while for PET/POSS2 and PET/POSS3 decreased by 24.4 o C and 13.7 o C, respectively. Introduction of any POSS type into PET have a strong influence on the crystalization of PET/POSS nanocomposites. Observed crystalinity of obtained nanocomposites changed from 34 % in PET to 19 % (for POSS3 0.2 weight percentage) and 43 % (for POSS2 0.2 weight percentage). Key words: PET/POSS nanocomposites, mechanical and thermal properties 1. INTRODUCTION Polyethylene terephtalate PET is one of the most versatile thermoplastics polymers used for production of fibers, films, bottles and technical products. In the past decade clay nanoparticles have been used to improve thermal stability and mechanical properties of polymers, which is the most effective when they are fully exfoliated. Successful melt exfoliation requires presence of strong interactions between clay and the polymer. Recently, polyoligomeric silsesquioxane POSS nanoparticles have attracted interest of polymer researches because the resulting nanocomposites are much improved in mechanical and thermal properties [1 6], mostly for PET/POSS nanocomposites. In this study three types of POSS (heptaisobuthylotrihydroxy POSS1; octatis dimethylosiloxy ethyloepoxy POSS2, and octatis dimethylosiloxy glicydoksypropylo POSS3) were incor- Dr hab. in. Institute of Materials Technology, Poznan University of Technology.
32 M. Szostak porated into PET by melt mixing. Thermal and mechanical properties of PET/POSS nanocomposites were investigated. 2. EXPERIMENTAL SET UP 2.1. Materials Bottle grade PET SKYPET type BL-8050 with an intrinsic viscosity of 0.80 dl g 1 supplied by SK EUROCHEM Co. was used in the study. Three kinds of POSS were obtained from the Chemical Department of Adam Mickiewicz University Poznan: 1. Heptaisobutylotrihydroxyoctasilsesquioxane (Figure 1a). 2. Octakisdimetylosiloxyetyloepoxycylohexylooctasilsesquioxane (Figure 1b). 3. Octatisdimetylosiloxyglicydoksypropylooctasilsesquioxane (Figure 1c). a) b) c) Figure 1. Chemical structure of used silsesquioxanes 2.2. Preparation of PET/POSS nanocomposites POSS/PET nanocomposites were prepared by two-step melt melting in onescrew extruder. Before each processing, PET was dried for 4 hours at 120 o C. The first the PET/POSS concentrates were produced with 5 weight percentage of three different types of POSS. In the second extrusion the PET/POSS nonocomposites were prepared with the POSS concentration of 0.2 and 0.5 weight precentage. In order to measure the mechanical properties, the standard injection moulded PET/POSS nanocomposites samples with dimension of 20 mm (wide) 145 mm (length) 4 mm (thickness) were used. The mechanical properties were measured using the Instron 4481 universal instrument. The drawing speed was 50 mm/min. Data was taken as averages of 7 measurements at the minimum. Thermal properties were investigated using differential scanning calorimeter (Netsch DSC 204 F1). The samples were heated to 290 o C at
Mechanical and thermal properties of PET/POSS nanocomposites 33 a heating rate 10 o C/min, cooled down to 20 o C at a cooling rate 20 o C/min and again heated to 290 o C with the same heating rate. 3. RESULTS AND DISCUSSION 3.1. Mechanical properties The tensile strength and modulus of PET and PET/POSS nanocomposites are shown on Figure 2 and 3, while the elongation at break in the Figure 4. Figure 2. Tensile strength of PET and PET/POSS nanocomposites The results of mechanical tests showed small changes in tensile strength of PET/POSS blends depending on the type of POSS used. The highest values of maximum stress was observed for POSS3, lower for POSS2 and the lowest for POSS1. The PET reference value was between the values for POSS1 and POSS2. The greatest elongation was measured for PET/POSS nanocomposites with 0.5 weight percentage of POSS1, then for reference PET and finally for PET/POSS3 and PET/POSS2 nanocomposites. The lower values of Young's modulus were observed for PET/POSS1 nanocomposites. For reference PET and PET/POSS2 and PET/POSS1 nanocomposites the tensile modulus remained constant.
34 M. Szostak Figure 3. Tensile modulus of PET and PET/POSS nanocomposites Figure 4. Elongation at break of PET and PET/POSS nanocomposites
Mechanical and thermal properties of PET/POSS nanocomposites 35 3.2. Thermal properties The melting and crystallization temperatures determined from heating and cooling curves as well as crystallinity of PET and PET/POSS composites are listed in Table 1 and shown in Figures 5 and 6. The results of DSC study showed that the melting point of all the tested polyesters and their nanocomposites with POSS are in the range from 249 o C to 251.2 o C (Figure 5). These values keep within the broader range of 248 o C to 252 o C, which is usually given by the manufacturers of PET granulates. In spite of small changes of melting temperature, it can be said that the increase of POSS content in the PET results in decrease in temperature of 1.1 o C for POSS1 and POSS2 and of 0.3 o C for POSS3, respectively. Thermal properties and crystallinity of PET and PET/POSS nanocomposites Table 1 PET/POSS samples Tm [ºC] Tc [ºC] Crystallinity [%] PET org 35s 250.9 197.4 19.2 PET org 60s 249.6 196.4 31.9 PET ref 249.4 199.7 34.2 PET+0.2%POSS1 251.2 204.8 33.5 PET+0.5%POSS1 250.1 192.7 33.2 PET+0.2%POSS2 250.1 175.3 43.3 PET+0.5P%OSS2 249 197.7 28.5 PET+0.2%POSS3 250.3 186 19.4 PET+0.5%POSS3 250 198.2 29.4 The effect of POSS content on crystallization temperature of PET/POSS nanocomposites is much larger (Figure 6). For the PET/POSS nanocomposite with 0.2 weight percentage of POSS1 the crystallization temperature is the highest 204.8 o C. It is about 5 o C higher than for the reference PET granulates and respectively about 7.4 o C and 8.4 o C compared to pure PET injected into molds at a temperature of 35 o C and 60 o C. For other silsesquioxanes crystallization temperature decrease of over 20 o C for POSS2 and over 10 o C for POSS3. Crystallization temperature for PET/POSS2 nanocomposites with 0.2 weight percentage of POSS2 is equal 175.3 o C, while for PET/POSS3 nanocomposites with the 0.2 weight percentage of POSS3 186 o C. The increase of POSS content in the PET to 0.5% in weight causes an increase of crystallization temperature to the level as for the reference PET.
36 M. Szostak Figure 5. Cooling DSC curves of PET and PET/POSS nanocomposites Figure 6. The second heating DSC curves of PET and PET/POSS nanocomposites Analyzing the degree of crystallinity of the tested PET/POSS nanocomposites, the measured values were in the range from 19 to 43 %. The highest degree of crystallinity was measured for the nanocomposites with 0.2 weight percentage of POSS2 in PET and the lowest for the nanocomposites with
Mechanical and thermal properties of PET/POSS nanocomposites 37 0.2 weight percentage of POSS3 in PET. PET with the degree of crystallinity below 20 % is suitable for the production of amorphous products (packaging) and with the crystallinity above 40 % for manufacturing of technical products (housing, fuel system components). 4. CONCLUSIONS 1. Results of mechanical testing show only small changes in mechanical properties (tensile strength, Young modulus and elongation at break) of tested PET/POSS nanocomposites dependending on POSS types use. The highest tensile strength and modulus were obtained for PET/POSS3 nanocomposites while the best elongation for PET/POSS1 nanocomposites. 2. The 0.2 weight percentage of POSS in PET/POSS nanocomposites significantly increase (POSS1) or decrease (POSS2 i POSS3) the crystallization temperature of that nanocomposites. The increase in temperature was 5.1 o C for PET/POSS1 while the decrease 24.4 o C and 13.7 o C for PET/POSS2 and PET/POSS3 were observed, respectively. 3. Introduction of any POSS type into PET strongly influence the crystallization of PET/POSS nanocomposites. Observed crystallinity of obtained nanocomposites change from 19 % (for 0.2 weight percentage of POSS3 in PET) to 43 % (for 0.2 weight percentage of POSS2 in PET). 4. Introduction of POSS into PET did not have a significant influence the melting temperature of the obtained PET/POSS nanocomposites. 5. Obtained results lead to a conclusion that observed influence of POSS types and its percentage contents in PET/POSS nanocomposites allow to design their properties in dependence on requirements set by customers. ACKNOWLEDGEMENTS This work was supported by Grant No. UDA-POIG.01.03.01-30-173/09 Silsesquioxane as a nanofillers and modifiers in polymer composites form European Regional Development Fund under the Operational Programme Innovative Economy 2007-2013.
38 M. Szostak REFERENCES [1] Kim H.U. et al., Morfology and mechanical properties of PET by incorporation of aminepolyhedral oligomeric silsesquioxane, Composities Science and Technology, 2008, 68, p. 2739 2747. [2] Kim J.K. et al., Morfology and rheological behaviours of poly(ethylene terephtalate) nanocomposites containing polyhedral oligomeric silsesquioxane, Journal of Applied Polymer Science, 2008, 107, p. 272 279. [3] Lee S.J. et al., Effects of clay and POSS nanoparticles on the quiescent and shear-induced crystallization behaviour of high molecular weight poly(ethylene terephthalate), Polymer Engineering and Science, 2009, p. 317 323. [4] Lim S.K. et al., Poly(ethylene terephthalate) and polyhedral oligomeric silsesquioxane nanohybrids and their physical characteristics, Journal of Material Science, 2010, 45, 5984 5987. [5] Yoon K.H. et al., Properties of poly(ethylene terephtalate) containing epoxy-functionalized polyhedral oligomeric silsesquioxane, Polymer International, 2005, 54, p. 47 53. [6] Zeng J. et al., Reinforcement of poly(ethylene terephtalate) fibers with polyhedral oligomeric silsesquioxanes (POSS), High Performers Polymers, 2005, 17 (3), p. 403 424. MECHANICZNE I TERMICZNE W A CIWO CI NANOKOMPOZYTÓW PET/POSS S t r e s z c z e n i e Nanokompozyty PET/POSS wytworzono przez mieszanie w stopie. Zbadano w a ciwo ci mechaniczne i termiczne nanokompozytów PET/POSS otrzymanych z trzech typów POSS (hepta (isobuthylo) tri-(hydroksy) POSS1; octatis dimethylosiloxy ethyloepoxy POSS2 i octatis dimethylosiloxy glicydoksypropylo POSS3) z dwoma wagowymi udzia ami procentowymi POSS w PET 0,2 % i 0,5 %. Nie zaobserwowano znacz cych zmian w a ciwo ci mechanicznych uzyskanych nanokompozytów PET/POSS, natomiast w a ciwo ci termiczne takich nanokompozytów zmieniaj si istotnie. Badania DSC wykaza y du y wp yw typu silsekwioksanu i jego procentowej zawarto ci na temperatur krystalizacji i krystaliczno badanych nanokompozytów PET/POSS. Zaobserwowano wzrost temperatury krystalizacji o 5,1 o C nanokompozytów PET/POSS1 oraz spadek odpowiednio o 24,4 C i 13,7 C kompozytów PET/POSS2 i PET/POSS3. Wprowadzenie do PET ka dego typu POSS wp ywa istotnie na szybko krystalizacji nanokompozytów PET/POSS. Zmierzony stopie krystaliczno ci otrzymanych nanokompozytów zmieni si z 19 % dla czystego PET do 34 % dla nanokompozytu PET/POSS o zawarto ci 0,2 % wag. POSS 3 i nawet do 43 % dla zawarto i 0,2 % wag. POSS 2 w PET. S owa kluczowe: nanokompozyty PET/POSS, w a ciwo ci mechaniczne i termiczne