Material propertiesTensile properties of PLLA/PCL composites filled with nanometer calcium carbonate
Introduction
Polycaprolactone (PCL) is one of the biodegradable polymeric materials. Biodegradable polymers have been quickly developed in recent decades and produced commercially. They have been widely used for production of bags, sacks and food packaging because these polymers prepared from renewable resources can undergo biodegradation upon disposal [1]. For improving further the processing and mechanical properties, PCL is usually modified by blending with other resins or filled with inorganic particles. Since the 1990's, PCL blend systems have been studied extensively, such as polyvinyl chloride (PVC)/PCL [2], styrene acrylonitrile (SAN)/PCL [3], polybutylene terephthalate (PBT)/PCL [4] and polystyrene (PS)/PCL [5] binary blend systems, as well as poly(epsilon-caprolactone)/poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/PCL blend systems [6]. Recently, a number of studies on fabrication and characterization of inorganic particle-filled PCL composites have been made [1], [7], [8], [9]. Roohani-Esfahaniand and co-workers [8] investigated the effects of bioactive glass nanoparticles on the mechanical and biological behavior of composite coated scaffolds. Xiao and his colleagues [9] researched the electro-active shape memory properties of poly(epsilon-caprolactone)/functionalized multiwalled carbon nanotube nanocomposite.
Poly (l-lactic acid) (PLLA) is one type of PLA. Due to its low molecular weight and relatively high cost, the applications of PLLA have been limited to pharmaceutical and biomedical uses. For improving further the processing and mechanical properties, PLLA is usually modified by blending with other resins or filling with inorganic particles [10], [11]. Wang and his colleagues [12] investigated the effects of calcium hydrogen phosphate (DCP) content on the mechanical properties, thermal and rheological behavior and phase morphology, as well as the toughening mechanism of PLLA/poly(butylene succinate) (PBS) blends, and found that the notched Izod impact strength of PLLA/PBS (80/20) blend significantly increased after the addition of 0.05-0.2 phr DCP, but the strength and modulus monotonically decreased with increasing DCP content.
Besides good biodegradable behavior, PLA and PCL have certain shape memory performance [13]. To improve the comprehensive performance of the biodegradable shape memory resins, PLA and PCL resins are usually modified through blending with other resin [14], [15] or filling with inorganic particles [7], [16]. More recently, the authors [10], [11], [17] researched the melt flow behavior in capillary extrusion of nanosized calcium carbonate respectively filled PLLA and PCL bio-composites, getting some interesting results.
Tensile mechanical properties, which include tensile modulus, tensile strength, tensile strength at fracture and elongation at break, are important for application performance of materials [18], [19], [20]. More recently, the authors [10], [11], [21] investigated the melt flow properties of nanometer calcium carbonate (nano-CaCO3) filled PLLA and PCL composites. However, there have been few studies on the tensile properties for PCL/PLLA blend and composites. The objective of this article is to investigate the effects of PCL content and tensile rate on the tensile properties of filled PLLA/PCL/nano-CaCO3composites.
Section snippets
Raw materials
The biodegradable PCL resin with the trademark of PCL6800 serving as a matrix material was supplied by Shenzhen Bright China Industrial Co. Ltd, China. The melt flow rate and density of the PCL were 10.3 g/10 min and 1.09 g/cm3, respectively.
The other biodegradable resin, PLLA with the trademark of AI-1001, also serving as a matrix material, was supplied by Shenzhen Bright China Industrial Co. Ltd, China. The melt flow rate and density of the PLLA were 7.5 g/10 min and 1.25 g/cm3, respectively.
Tensile curves
Fig. 1 shows the tensile stress strain curves of the PLLA/PCL/nano-CaCO3 composites at a rate of 10 mm/min. It can be seen that the maximum tensile stress for PLLA resin is reached at a tensile strain about 9%, and the tensile strain at the maximum tensile stress for the composites increases with increasing PCL content. The elongation at break increases, while the maximum tensile stress decreases with increase of the PCL content. When the PCL weight fraction is more than 40%, the composites
Conclusions
The influence of the PCL content and tensile rate on the tensile mechanical properties of PLLA/PCL/nano-CaCO3 composites was significant. With increasing PCL weight fraction, the tensile elastic modulus, tensile strength and tensile strength at fracture decreased nonlinearly. When the PCL weight fraction was constant, the tensile elastic modulus, tensile strength, tensile strength at fracture and tensile elongation at break of the PLLA/PCL/nano-CaCO3 composites increased slightly with an
Acknowledgement
The authors would like to thank for the support from the Research Committee of the Hong Kong Polytechnic University (Project code: G-U844).
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