ВЫСОКОМОЛЕКУЛЯРНЫЕ СОЕДИНЕНИЯ, Серия А, 2011, том 53, № 2, с. 239-247
КОМПОЗИТЫ
УДК 541.64:547.915
PREPARATION OF POLYLACTIC ACID/EPOXIDIZED PALM OIL/FATTY NITROGEN COMPOUNDS MODIFIED CLAY NANOCOMPOSITES
BY MELT BLENDING1 © 2011 г. Emad A. Jaffar Al-Mulla
Department of Chemistry, College of Science, University of Kufa, AnNajaf, Iraq e-mail: emadaalmulla@yahoo.com Received March 21, 2010 Revised Manuscript Received July 9, 2010
Abstract—In this study, new biopolymer nanocomposites have been prepared. Fatty nitrogen compounds (FNCs); fatty amide (FA), fatty hydroxamic acid (FHA), and carbonyl difatty amide (CDFA), which were synthesized from palm oil, have been used as one of organic compounds to modify natural clay (sodium montmorillonite). The clay modification was carried out by stirring the clay particles in an aqueous solution of FA, FHA, and CDFA by which the clay layer distance increases from 1.23 to 2.71, 2.91 and 3.23 nm, respectively. The modified clay was then used in the preparation of the polylactic acid/epoxidized palm oil (PLA/EPO) blend nanocomposites. The interaction of the modifier in the clay layer was characterized by X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Elemental analysis was used to estimate the presence of FNCs in the clay. The nanocomposites were synthesized by melt blending of the modified clay and PLA/EPO blend at the weight ratio of 80/20. The nanocomposites were then characterized using XRD, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and tensile properties measurements. The XRD and TEM results confirmed the production of nanocomposites. PLA/EPO modified clay nanocomposites show higher thermal stability and significant improvement of mechanical properties in comparison with those of the PLA/EPO blend.
INTRODUCTION
Biodegradable polymers have recently much attracted in the scientific community due to a rapid growth of intensive interest in the global environment as alternative of petroleum-based polymeric materials.
One of the most promising candidates of biodegradable synthetic polymers is PLA [1]. PLA can be obtained from renewable resources by means of a fermentation process using sugar from corn either by ring-opening polymerization or by condensation polymerization. It is linear aliphatic thermoplastic polyester and is readily biodegradable by enzymatic way [2-4].
In addition to its application in textile industries, automotive and clinical uses, PLA represents a good candidate to produce disposable packaging due to its good mechanical properties and processability [5-7]. However, high tensile, high modulus, low elongation at break and high price limit its application. Therefore, the tailoring of its properties to reach end-users demands is required.
Attempts have been made to enhance the flexibility and other mechanical properties by blending of PLA with other polymers such as polycaprolactone, poly-butylene succinate or polyetherurethane [8-11]. Low molecular weight plasticizers such as polyethylene gly-
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col, polypropylene glycol and citrate esters were also used to improve of the thermal and mechanical properties of PLA [12-15].
The incorporation of organoclays in the polymer to produce nanocomposite is another mean to modify the property balance of a material. The improvements in thermal stability, physical and mechanical properties can be achieved by addition of 2-5 wt% of organoclays in comparison to the neat polymer [16-18].
The modifying natural clay (montmorillonite) may carried out via exchanging the original inter-layer cations by organic cations where transform from organo-phobic to organophilic materials and significantly increase the basal spacing of the clay layers [19]. It is generally accepted that the extent of swelling depends on the length of the alkyl chain and the cation exchange capacity of the clay [20]. Organoclays are mainly obtained by exchanging cations in the clay minerals which contain hydrated Na+ ions with alkyl-amidonium [21].
Processing and properties of PLA/thermoplastic starch/montmorillonite nanocomposites were investigated and characterized using X-Ray diffraction, transmission electron microscopy and tensile measurements. The results show improvement in tensile modulus and strength and to a reduction in fracture toughness [22].
Table 1. The optimization of basal spacing of modified montmorillonite with different amounts of fatty nitrogen compounds and hydrochloric acid
Amount of FNCs (g) in 4.00 g of MMT Conc. HCl, ml d- spacing, nm
FA-MMT FHA-MMT CDFA-MMT
1.00 4.00 1.29 1.32 1.59
1.50 4.00 1.30 1.39 1.77
2.00 4.00 1.34 1.44 1.85
2.50 4.00 1.40 1.54 1.91
3.00 4.00 1.45 1.60 2.03
3.50 4.00 1.50 1.67 2.10
4.00 4.00 1.55 1.73 2.19
4.50 4.00 1.62 1.82 2.27
5.00 4.00 1.63 1.83 2.29
4.50 6.00 1.72 2.01 2.48
4.50 8.00 1.87 2.29 2.59
4.50 10.00 2.01 2.42 2.72
4.50 12.00 2.12 2.61 2.91
4.50 14.00 2.41 2.74 3.11
4.50 16.00 2.69 2.89 3.21
4.50 18.00 2.70 2.91 3.22
Plasticized PLA based nanocomposites were prepared and characterized with polyethyleneglycol and montmorillonite. It is reported that the organo-modi-fied montmorillonites-based composites have shown the possible competition between the polymer matrix and the plasticizer for the intercalation between the alumino-silicates layers [23].
In this study, fatty nitrogen compounds (FNCs) synthesized from palm oil were used for modification of montmorillonite. The presence of long chains fatty acids (mainly 16 and 18 carbon atoms) in FNCs containing O and N donor set suggests FNCs should be very useful as surfactants for clay modification. The use of FNCs reduces the dependent on petroleum based surfactants. The present study show plasticized PLA based nanocomposites with epoxidized palm oil (EPO) and montmorillonite modified by DNCs. EPO is an epoxidized derivative of a mixture of esters of glycerol with various saturated and unsaturated fatty acids. It is important for many chemical industries as they are derived from renewable, biodegradable, environmental friendly and easily available raw materials.
EXPERIMENTAL
Materials
Epoxidized palm oil was provided by Advanced Oleochemical Technology Division (AOTD), Malaysia. Sodium montmorillonite (Kunipia F) was ob-
tained from Kunimine Ind. Co. Japan. Polylactic acid and chloroform were purchases through local suppliers from T.J. Baker, USA and Merck, Germany, respectively.
Preparation of Organoclay
Organoclay was prepared by cationic exchange process where Na+ in the montmorillonite was exchanged with alkylamidonium ion from FNCs synthesized from triacylglycerides, which were reported in our previous papers [24—26], in an aqueous solution. 4.00 g of sodium montmorillonite (Na-MMT) was stirred vigorously in 600 ml of hot distilled water for one hour to form a clay suspension. Subsequently, designated amount of fatty nitrogen compounds which had been dissolved in 400 ml of hot water and desired amount of concentrated acid hydrochloride (HCl) was added into the clay suspension of fatty nitrogen compounds. After stirred vigorously for one hour at 80°C, the organoclay suspension was filtered and washed with distilled water until no chloride was detected with 1.0 M silver nitrate solution. It was then dried at 60 °C for 72 hours. The dried organoclay was ground until the particle size was less than 100 ^m before the preparation of nanocomposite. The amounts of hydrochloric acid, and FNCs used in this study were listed in Table 1.
Preparation of PLA/EPO—clay Nanocomposites
The designed amount of PLA/EPO ratio were prepared by an internal mixer (Haake Polydrive), using different conditions (temperature, speed and time) in order to obtain the optimum conditions which were 185°C, 50 rpm and 12 minutes, respectively. To prepare a sample of the composite, a specific amount of PLA was first melted and mixed thoroughly with appropriate amount of PCL for 2 minutes. Various amounts of organoclays (1, 2, 3, 4, and 5%) were incorporated into the blend in the third minute. The mixture was compressmoulded into sheet of 1 mm thickness sheets under a pressure of 100 kg cm-1 in a standard hot press at 150°C for 15 min, and cooled pressed process for 10 minutes to obtain a good blend film. The amount of PLA/EPO and the modified clay used in this study are listed in Table 2.
Characterization
X-Ray diffraction (XRD) analysis. X-ray Diffraction (XRD) study was carried out using Shimadzu XRD 6000 diffractometer with CuK radiation (X = = 0.15406 nm). The diffractogram was scanned in the ranges from 2° to 10° at a scan rate of 1° min-1.
Fourier transform infrared (FTIR) spectroscopy. The FTIR spectra of the samples were recorded by the FTIR spectrophotometer (Perkin Elmer FT-IR-Spectrum BX, USA) using KBr disc technique.
Elemental analysis. Elemental analyzer (LEO CHNS-932) was used for quantative analysis of nitrogen contents in the organoclay. The determination was carried out under N2 atmospheric conditions using the sulfamethazine as a standard.
Thermogravimetric analysis (TGA). The thermal stability of the samples was studied by using Perkin Elmer model TGA 7 Thermogravimetry Analyzer. The samples were heated from 35 to 800°C with the heating rate of 10°C/min under nitrogen atmosphere with a nitrogen flow rate of 20 mL/min.
Transmission electron microscopy (TEM). The dispersion of clay was studied by using Energy Filtering Transmission Electron Microscopy (EFTEM). TEM pictures were taken in a LEO 912 AB Energy Filtering Transmission Electron Microscope with an acceleration voltage of 120 keV. The specimens were prepared using a Ultracut E (Reichert and Jung) cryomicro-tome. Thin sections of about 100 nm were cut with a diamond knife at —120°C.
Tensile properties measurements. The tensile strength, tensile modulus and elongation at break were measured by using Instron Universal Testing Machine 4301 at 5 mm/min of cr
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