Magnetism and structure of nanocomposites made from magnetite and vegetable oil based polymeric matrices

https://doi.org/10.1016/j.matchemphys.2016.02.071Get rights and content

Highlights

  • Interparticle interactions are controlled by adjusting the matrix components.

  • Particle aggregation into the matrices was monitored by the Fractal Aggregate Model.

  • Magnetization results were analyzed by the Interacting Superparamagnetic Model.

  • Bio-based magnetic nanocomposites are promising materials in industrial applications.

Abstract

The aim of this work is to study the influence of the polymeric matrix composition on particle aggregation, magnetic interparticle interactions and nanoparticle surface effects, which affect the magnetic and structural properties of different ultra-diluted magnetite nanocomposites (MNCPs). Bio-based matrices were selected as a possible response to the increasing demand for renewable materials. To investigate the influence of different bio-based polymeric matrices on the magnetic behavior, three different bio-based polymers were used to prepare MNCPs with 1 wt.% of magnetite nanoparticles (MNPs). One of them was prepared using a tung oil (TO)/styrene (St) weight ratio of 70/30, a second one was prepared by replacing the styrene with methylester (green comonomer obtained from tung oil, ME, 70TO/30ME) and a third one that incorporated a green modifier, acrylated epoxidized soybean oil (AESO), using a tung oil/AESO weight ratio of 90/10. Structural features as nanoparticle aggregation state, nanoparticle and cluster sizes, and fractal dimension were studied and determined from small-angle X-ray Scattering (SAXS). The experimental SAXS data were analyzed by means of fractal aggregate model. Results indicate differences in nanoparticle arrangement depending of the containing matrix. The magnetic characterization of these materials indicates that the matrix strongly affects the physical and chemical properties of the MNCPs. All samples display superparamagnetic behavior at room temperature, but the blocking temperature varies from 75 K (tung oil/styrene with 1 wt.% MNPs) to 126 K (tung oil/AESO 1 wt.% MNPs). Furthermore, the temperature dependence of the coercive field changes for all samples, suggesting a strong influence of the polymer properties on the magnetic properties of the MNCPs.

Introduction

The production of polymeric bio-based nanocomposites has become an important area of research and development due to the potential applications of these materials in different scientific and industrial fields [1], [2] as well as biotechnology and biomedicine [3]. Particularly, in pharmaceutical applications, it is possible to control the drug delivery by using polymeric materials loaded with magnetic nanoparticles which are activated with external magnetic fields [4], [5], [6]. When a magnetic field is applied over a magnetic nanocomposite, drugs previously loaded into the MNCP can be released. On the other hand, the bio-based nanocomposites have numerous applications in the aircraft, automobile and machine industries, where they can be used for noise reduction and prevention of vibration induced fatigue failure [7].

In order to develop technological applications, cheap and easy-to-obtain magnetic nanocomposites are preferable. Specifically, the development of polymeric composites obtained from renewable raw materials additionally presents several environmental advantages [8], [9]. These bio-based nanocomposites can be described as bio-based matrices reinforced with magnetic nanoparticles [1], [3], [10]. Even though in the recent years the production of these kind of materials has grown considerably, few authors use vegetable oils as raw materials to prepare nanocomposites using magnetite nanoparticles as fillers [11], [12], [13].

Physico-chemical properties of this class of MNCPs are regulated by several factors, such as type of magnetic particles, size, polydispersity, coating and concentration within the matrix, as well as the chemical nature of the containing matrix, among others. In the last few years, the ability to control the aforementioned aspects has led to a number of potential applications. Some of these are centered on the fact that the magnetic nanoparticles can be thermally activated by an alternating magnetic field, producing a release of heat, which under specific conditions, can be used to change the mechanical properties of the MNCPs, e. g. stress for MNCPs for shape memory or actuators, diffusion coefficient for MNCPs for drug delivery, etc [14], [15], [16], [17], [18], [19], [20], [21]. Such release of heat also can be exploited for hyperthermia treatment of cancer [22], [23], [24], [25], in this sense and according to latest reports, increase in magnetic interactions between nanoparticles amplifies the specific absorption rate (SAR) [22], [23], which is an important parameter to take in account for hyperthermia treatments. Usually, to obtain polymer-magnetic nanocomposites with higher interparticle interactions is necessary to increase the percentage of magnetic nanoparticles with respect to the total volume of the composite. However, for in-vivo applications, such as magnetic hyperthermia, an increase in the amount of magnetic nanoparticles may not be viable. Thus, it is necessary to find alternatives that would allow enhancing the magnetic interparticle interactions without increasing the nanoparticle concentration. Concerning this we explore a way to increase the interparticle interactions by adjusting the matrix components, but keeping the nanoparticle concentration constant.

In a previous work [12], superparamagnetic polymer nanocomposites were prepared from the incorporation of magnetite nanoparticles (1 and 9 wt.%) into a matrix composed by tung oil and styrene using a weight ratio of 50/50. We studied the morphology, dynamic-mechanical and mechanical properties of these MNCPs, as well as basic magnetic properties, from which we concluded that they were significantly affected by the variation of the concentration of the MNPs.

From previous results, we inferred that it would be necessary to consider systems with low concentration of MNPs (1 wt.%) in other matrices, in order to study how the interaction among the MNPs and the matrices affects the thermal, dynamic-mechanical, mechanical and magnetic properties, among others. Considering this objective, three novel matrices with 1 wt.% of MNPs concentration were prepared. The same matrices without MNPs were also prepared and previously characterized [26]. The first one was prepared using a tung oil/styrene weight ratio of 70/30 (called S1). A second one (called S2) was prepared replacing the styrene monomer for methylester (ME), which is a green monomer (obtained by transesterification of the tung oil with methanol) in the same weight ratio (70/30). Finally, a last one (called S3), consisted in the incorporation of a green modifier, a commercial acrylated epoxidized soybean oil (AESO), using a tung oil/AESO weight ratio of 90/10.

Small angle X-ray scattering method was used to investigate the structure of the MNPs within the non-magnetic matrix. Cluster formation was followed by means of the fractal aggregate model. Magnetic experimental results were analyzed by means of the interacting superparamagnetic model (ISP) [27] that takes into account magnetic interactions of dipolar origin. This model gives an indirect analysis of MNP aggregations in the MNCPs, obtaining an excellent agreement for magnetic nanocomposites with low MNPs concentration (1 wt.%). When the ISP model is used in magnetic nanocomposites with concentrations higher than 1 wt.% spurious results appear as a consequence of stronger–dipolar interactions among MNPs, possibly due to a more compact agglomeration of the nanoparticles.

The aim of this work is to study more exhaustively the magnetic and structural properties of bio-based nanocomposites synthesized from different bio-based polymeric compounds, which were used as support matrix for magnetite nanoparticles (1 wt.%). Magnetic results of the three samples synthesized for this work are compared with those already reported for a sample made from tung oil and styrene with 1 wt.% MNPs [12].

Section snippets

Materials

The vegetable oil used, tung oil (TO), is a triester of glycerol and fatty acids, being the major fatty acid constituent α-elaeostearic acid (84 wt.%). The monomers used in the copolymerization with tung oil were: styrene (St) 99.95% pure supplied by Cicarelli and a monomer synthesized in our laboratory, methylester from tung oil (ME) obtained by transesterification reaction [26]. The modifier was a commercial acrylated epoxidized soybean oil (AESO) purchased from Sigma–Aldrich. Boron

Thermogravimetric analysis (TGA)

TGA analysis of the materials with and without 1 wt.% of MNPs was performed to evaluate the effect of the addition of magnetic nanoparticles on the thermal degradation of the composites.

Fig. 1 shows the TGA curves of the magnetic (M1, M2 and M3) and non-magnetic (S1, S2 and S3) samples. MNCPs loaded with 1 wt.% of MNPs have a similar weight loss than the original matrices in the temperature range 420–620 K. The most important differences with respect to the degradation of the original matrices,

Conclusions

Physicochemical properties of novel synthesized ultra-diluted green nanocomposites, based on a vegetable oil and 1wt.% of magnetite nanoparticles coated with oleic acid, were studied.

The glass transition temperature (Tg) of the three nanocomposites increased due to incorporation of 1wt.% of MNP as a consequence of the different relaxation mechanisms and inhomogeneities that appeared in the materials because of the presence of the magnetic nanoparticles. The storage modulus and mechanical

Acknowledgments

The work at UNICAMP was supported by FAPESP (2011/01235-6, 2011/02356-11, and 2014/26672-8) and CNPq (506394/2013-1) Brazil. Small-angle X-ray scattering data were acquired at beamline D11A-SAXS1 (17036), D11A-SAXS2 (14355) at LNLS (Campinas, SP, Brazil) and SEM images (17596) were taken at the LNNano of National Nanotechnology Laboratory (CNPEM, Campinas, Brazil). The authors thanks M. E. F. Brollo for help during the SAXS acquisitions and Cooperativa Agrícola de Picada Libertad for the supply

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