This article describes the results of an investigation on the influence of loading silane treated sugar cane bagasse (SB) on the morphology and properties of recycled polypropylene (rPP). The samples are prepared through melt extrusion followed by injection moulding. The Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) results show that SB-rPP composites have a fairly strong interfacial interaction and a change in crystallization for the highest containing SB composite, however, some fibre pull-outs are observed as the SB content is increased. The interaction influences the thermal and mechanical properties of the samples in a complex way. There are strong indications of a stronger interfacial interaction on the highest containing SB composite, which is supposedly accountable for the increased crystallinity and melting temperature.
Interest in composite materials reinforced with natural fibres has recently increased considerably due to some natural benefits of the fibres. These materials present low cost, low density, high specific properties and are biodegradable [
Neto et al. [
Nonetheless, the greatest drawback to the utilization of natural fibers is related to matrix/filler adhesion due to the fact that natural fibers are hydrophilic and the polymeric matrix is hydrophobic, yielding composites with poor mechanical properties. In order to overcome the problem, many papers have reported that the modification of fibers surface increases the compatibility between the matrix and the reinforcement. In fact, most of these publications have used the same treatments, which are alkaline, acetylation and bleaching [
One of the important commonly applied commercial polymer that received a minimum attention as a matrix of sugar bagasse filler is polypropylene (PP). PP is widely used in packaging and in a variety of other applications due to their great potential in terms of barrier properties, brilliance, dimensional stability and processability. As the use of the material widens, the waste disposed of into the environment also escalates. It is for that reason recycled PP (rPP) is used in this study. Besides, rPP has higher biodegradation rate compared to PP [
SB was supplied by a farm in Craddock near Port Elizabeth, South Africa. 3-aminopropyl tri-ethoxysilane was purchased from Sigma Aldrich, South Africa. All chemicals were used as received without further purification.
1% solution 3-aminopropyl tri-ethoxysilane (A1100) was prepared by mixing the silane with an ethanol/water mixture in the ratio 6/4. The pH of the solution was adjusted to 4 with acetic acid. The SB was soaked in the solution and allowed to stand for 2 hours. The silane solution was drained out and the fibres were washed with distilled water. Finally the SB was dried in an oven at 70˚C until completely dry.
A co-rotating twin-screw extruder (CTE-20, Coperion, China) equipped with a main feeder and side feeder as well as a strand pelletizer with an L/D ratio of 40 was employed to compound the rPP and SB. SB and rPP were dried in a convection oven at 40˚C for 24 h before extrusion. The temperature profile during extrusion was set from 160˚C - 170˚C and screw speed was maintained at 40 rpm.
BOY 22M (Germany) injection moulding machine was used to form dumbbell of rPP/SB composites.
FTIR of the samples were carried out on a Spectrum 100 FTIR (Perkin Elmer, Waltham, MA, USA). The range used was between 500 and 4000 cm−1.
XRD patterns of the samples were recorded using Philips PW 1830 X-ray diffractometer with Cu Kα radiation (λ = 0.154 nm). The crystallinity index (CI) was determined by using XRD deconvolution method.
Thermogravimetric analysis was carried out with a Perkin Elmer Pyris 1 TGA. The analyses were done under flowing nitrogen at a constant flow rate of 20 mL∙min−1. The samples (5 - 10 mg) were heated from 25˚C - 600˚C at a heating rate 10˚C∙min−1.
The DSC analyses were performed on a Perkin Elmer Pyris-1 differential scanning calorimeter (Waltham, Massachusetts, USA). The analyses were performed under flowing nitrogen (20 mL∙min−1). The instrument was calibrated using the onset temperatures of melting of indium and zinc standards, as well as the melting enthalpy of indium. 5 - 10 mg samples were sealed in aluminium pans, heated from 0˚C to 160˚C at a heating rate of 10˚C∙min−1, and cooled at the same rate to 0˚C. For the second scan, the samples were heated and cooled under the same conditions. The onset and peak temperatures of melting as well as crystallization enthalpies were determined from the second scan. At least three different samples from each composite were analysed, and the average and standard deviation values for each property were calculated.
The tensile strength of the composite samples were measured according to ASTM methods D882 (E) using an Instron model 3369 testing machine (Instron, Morwood, Massachusetts, USA) at a strain rate of 10 mm∙min−1.
pull-outs and breakage of fibres. More fibre ends appeared in the highest SB containing composites (indicated by the arrows) with the larger fibre pull-outs, although some remained trapped in rPP. The pull-outs in both 15% and 25% SB (
where Acryst and Aamorp are the fitted areas of the crystal and amorphous domains, respectively.
Pure rPP showed well known prominent peaks in the 2θ range of 15 - 30, which correspond to monoclinic α-crystalline phase [
Sample | Ac | At | CI (%) |
---|---|---|---|
rPP | 44,451 | 98,939 | 31 |
SB-rPP 5 wt.% | 37,115 | 111,345 | 25 |
SB-rPP 15 wt.% | 37,040 | 157,907 | 19 |
SB-rPP 25 wt.% | 32,616 | 83,869 | 28 |
results were observed by Mi et al. [
The addition of SB decreased the intensities of most peaks, more evident from approximately 800 to 1100 cm−1, and an appearance of new peak at 1022 cm−1. Some of the peaks from the spectrum of SB-rPP 25 wt.% in the range are either not observed or much less intense. The decreased intensities could be due to the reorientation of polymeric chains as the results of interaction with SB fibres, whereas the significant intensity reduction in SB-rPP 25 wt.% spectrum could either be attributed to a change in crystal structure observed in XRD and/or a strong interfacial adhesion. The appearance of the new peak could results from the interfacial interaction between rPP and siloxane bridges of the natural fibres [
closer to the amount of sugar cane bagasse. That is confirmed by well resolved DTG’s first and second peaks around 340˚C and above 400˚C respectively. The two decomposition steps could, therefore, be attributed to the sugar cane bagasse and matrix decompositions respectively. The addition of SB significantly increased the thermal stability by approximately 50˚C difference compared to the pure rPP. This is further indicated in DTG by the shift of the major peaks, attributed to rPP degradation, to higher temperatures. Contrary to our trend, some researchers observed a decrease in thermal stability of SB-PP composites and related the observations to lower thermal decomposition temperatures of SB and moisture content [
The DSC curves for the samples are shown in
The melting enthalpy of 100% crystalline polymer, ∆H∞, was taken as 207 J∙g−1 for rPP [
A correction for diluting effect linked to the filler incorporation in the matrix was made when calculating the normalised melting enthalpy
From
The influence of sugar cane content on the modulus, stress and elongation at break of the different composites are shown in
Sample | Second heating | |||
---|---|---|---|---|
Tp,m(˚C) | χc/% | |||
rPP | 164.2 ± 0.4 | 80.0 ± 1.3 | 80 | 38.6 |
SB-rPP-5 wt.% | 163.9 ± 0.7 | 66.9 ± 1.5 | 70.4 | 34 |
SB-rPP-15 wt.% | 163.9 ± 0.5 | 52.5 ± 1.7 | 61.8 | 29.9 |
SB-rPP-25 wt.% | 166.4 ± 0.2 | 48.4 ± 0.2 | 64.5 | 31.2 |
tent (
The elongation at break of all SB-rPP composites decreases with an increase in SB content, although the effect is less significant in the highest containing SB composite (
Sugar cane bagasse-recycled polypropylene composites were successfully prepared by aninjection moulding technique. SEM analysis showed evidence of strong rPP-SB interface despite fibre pull-outs at higher SB contents. XRD results showed that the addition of SB decreased crystallinity and induced β-crystal growth in the highest SB containing composite. The β-crystal formation led to an improved crystallinity of the composite. FTIR analysis indicated that an addition of SB decreased intensities of most peaks and the observation was pronounced in the highest SB containing composite. The addition of SB improved thermal stability of all composites and the higher SB containing composite was the most thermally stable. The interaction of SB with the polymer led to the improved crystallinity, melting temperature and mechanical properties.
This paper forms part of a research project, “Greener Cities in South Africa”, funded by the Green Fund, an environmental finance mechanism implemented by the Development Bank of Southern Africa (DBSA) on behalf of the Department of Environmental Affairs (DEA) and CSIR. Opinions expressed and conclusions arrived at are those of the author and are not necessarily to be attributed to the Green Fund, DBSA or DEA.
Tshwafo E.Motaung,Linda Z.Linganiso,MayaJohn,Rajesh D.Anandjiwala, (2015) The Effect of Silane Treated Sugar Cane Bagasse on Mechanical, Thermal and Crystallization Studies of Recycled Polypropylene. Materials Sciences and Applications,06,724-733. doi: 10.4236/msa.2015.68074