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Macromol. Symp. 2012, 315, 24–29
DOI: 10.1002/masy.201250503
Thermal, Mechanical and Morphological Behavior of Poly(propylene)/Wood Flour Composites R. Adhikari,*1 N. L. Bhandari,1 H. H. Le,2 S. Henning,3 H.-J. Radusch,2 G. H. Michler,3 M.-R. Garda,4 J. M. Saiter4
Summary: The comparative studies on the thermal, mechanical and morphological behavior of compression molded poly(propylene) (PP)/wood flour (WF) composites were performed using wood flours (WFs) of different origins. The comparison has been made on the basis of results obtained from thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and tensile testing. It has been demonstrated that an addition of 5 wt.-% of maleic anhydride grafted polypropylene (PP-g-MA) has a significant effect on the morphological and thermomechanical behavior of the composites. Although, microscopic examinations revealed no significant differences in the morphology of the compatibilized composites, a remarkable improvement of thermal degradation behavior was observed. From the view point of mechanical properties, the composites with high amount of filler (60 wt.-%) showed similar behavior irrespective of the origin of wood flour. Keywords: DSC; electron microcopy; poly(propylene); wood flour
Introduction In recent years, polymer composites reinforced with bio-based lingo-cellulosic filler have become attractive areas of research activities that are aimed at the development of more environmentally friendly materials. In addition to their use as fillers for green polymer composites,[1] the natural fibers are introduced also into petroleum based polymers. The recent trends of polymer based composite researches have been mainly motivated by two reasons. First, the natural fibers are easily available (sometimes as waste materials, by-products 1
2
3
4
Central Department of Chemistry, Tribhuvan University, Kirtipur, Kathmandu, Nepal E-mail:
[email protected] Center for Engineering Sciences, Martin Luther University Halle-Wittenberg, Geusaer Str. Geb. 131, D - 06217 Merseburg, Germany Institute of Physics, Martin Luther University HalleWittenberg, D - 06099 Halle/Saale, Germany Laboratoire LECAP, Institut des Mate´riaux de Rouen, Universite´ de Rouen, Avenue de l’Universite´, BP 12, 76801, Saint Etienne du Rouvray, France
of different industries) and are biodegradable and renewable. Second, the natural fibers are low cost materials endowed with high strength and their easy processing into the polymer matrix. Nevertheless, one also has to take into account that the physical properties of such natural fiber modified composites exhibit a large scattering of the data sometimes reaching up to 100%. The common fillers of both scientific and economical interest have been the flours or fibers derived from wood flour,[2–8] rice husks,[8,9] natural fibers such as flax, sisal, kenaf, kraft, jute etc.[10–13] and sometimes, besides the use of plant based fibers even the rests of shell and scales bearing animals such as fish scales.[14] Particular attention has been paid in many studies on use of agricultural and carpentry wastes (such as rice husks, cotton rests, saw dusts etc.[2–4,15]) as filler in the new kinds of composite materials. In the literature, a large volume of references concerning the processing, properties and morphological aspects of natural fillers in thermoplastics polyolefins,[15,16]
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Macromol. Symp. 2012, 315, 24–29
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[17]
[14]
polyesters and thermosetting resins can be found. A thorough survey of the literature works makes it evident that, besides choice of proper coupling agent, the selection of suitable processing route (such as filler aspect ratio,[6] twin screw extrusion or single screw extruder),[7] micromechanical behavior of such composites,[18,19,20] their reclyclability[21] and rheological properties[22] are important issues to be taken into account for the development of new polymeric composites. On the other hand, in spite of a large number of works on several reinforcing natural fibres with synthetic polymers, a clear picture of structure-property relationships has not been obtained so far. Thus, there is still a need of systematic study of the correlation between morphology and deformation behavior of such composites, particularly with filler as majority phase. Thus, to begin with, the aim of the present paper is to study the thermal, mechanical and morphological properties of the composites of polypropylene with carpentry waste of Shorea robusta and Dalbergia sissoo (which come directly from the carpentries in Kathmandu) and compare their properties with the composites made up of commercially available European wood flour.
Experimental Part Materials The polymer used in this study is a commercial polypropylene homopolymer (Moplen PP562N) supplied by Basell Chemical Company with melt flow index of 11g/10 min. Three different kinds of wood flours named as WF1, WF2 and WF3 were used as fillers. (see Table 1). Maleic
anhydride grafted polypropylene (MA-gPP) used as compatibilizer was Exxelor PO 1020 (ExxonMobile). Sample Preparation The wood flours obtained from the carpentries were ground to fine powders, filtered through the sieves of various diameters (ranging from 180 mm to 500 mm) and stored in a vacuum oven for 12 h at a temperature of 80 8C. PP and WFs were mixed in different weight ratios (90/10, 80/20, 60/40 and 60/40). Two sets of samples were prepared: the composites containing pristine PP matrix and the composites having matrix containing 5 wt.-% of MA-g-PP. The diameter size of the WF particles was set to the range 180–250 mm. For the preparation of the composites, the components were mixed in an internal mixer at temperature of 170 8C for 5 min followed by compression molding to 1 mm thick plates at 180 8C and 120 bar for 2 min. Thermal Analysis Thermal studies were performed by means of thermogravimetric measurements using TGA 209 balance (Netzsch, Germany) in nitrogen atmosphere from 10 to 250 8C at a heating rate of 10 8C/min. The calorimetric measurements were performed with a differential scanning calorimeter DSC 2920 (TA Instruments, USA) under a nitrogen ambience (100 ml/min) with a heating rate of 10 8C/min within a temperature range of 0 8C to 180 8C. Mechanical Testing Tensile bars having a total length of 50 mm were prepared from the compression molded plates and strained at a crosshead speed of 50 mm/min at 23 8C using a Zwick universal tensile machine. At least 5
Table 1. Information about the wood flours used in this work. Designation WF1 WF2 WF3
Supplier
Source Tree
Native color
Wood Company, Finland Carpentry in Kathmandu Carpentry in Kathmandu
– Sorea robusta Dalbergia Sisaoo
light yellow brown brown
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Macromol. Symp. 2012, 315, 24–29
Normalized Heat Flow
Endo PP W3C5-60
W2C5-60
W1C5-60
60
80
100
120
140
160
180
Temperature (°C)
Figure 1. Comparison of DSC plots of PP and compatibilized PP/60 wt.-% wood flour composites comprising different kinds of flours.
Electron Microscopy Scanning electron microscopy (SEM) (JSM 6300, JEOL) was used to visualize the structural details of the composites using freshly cryofracturted surfaces. The surfaces were sputtered coated with thin gold film to avoid charging and irradiation damage during the SEM inspection of the samples.
Results and Discussion Characterization of Composites by Thermal Analysis Figure 1 shows DSC curves of PP/60 wt.-% wood flour composites in comparison with that of pure PP at temperatures ranging from 30 8C to 200 8C. In order to eliminate the influence of the processing history of the samples, the thermograms obtained during second heating runs are presented. In case of pure polymer, a heat flow peak centered around 1608C can noticed which corresponds to the melting point of isotactic polypropylene (iPP). The thermal degradation behavior of the composites exemplified by PP/60 wt.-% WF2 is presented by mass loss curve and
differential curves in Figure 2. The degradation of sample leading to almost no residual mass (which is
