Novel Biocomposites from Microfibrillated Cellulose...
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Novel Biocomposites from Microfibrillated Cellulose grafted with Poly(ε-caprolactone) – Synthesis and Characterization Hanna Lönnberg, Linda Fogelström, Lars Berglund, Eva Malmström, and Anders Hult * Dept. of Fibre- and Polymer Technology, The Royal Institute of Technology, SE-10044 Stockholm, Sweden KEYWORDS: biocomposites, microfibrillated cellulose, grafting of polymer, ring-opening polymerization, poly(ε-caprolactone), thermal and mechanical properties INTRODUCTION Environmental concerns have led to a rapid growing interest in replacing traditional petroleum-based technology with more green alternatives. Cellulose, one of the main components in plants, is a biodegradable and renewable recourse. The use of cellulose fibers, instead of traditional fibers such as glass and carbon, offers a way to make more environmental friendly biocomposites. By replacing the traditional fibers with cellulose fibers several benefits are achieved, such as low density, low cost, good specific mechanical properties, reduced tool wear, and biodegradability.[1] Microfibrillated cellulose (MFC) is moderately degraded, nano-sized cellulose, which exhibits unique properties with high modulus and strength, and at the same time a high aspect ratio.[2] These are important properties for development of novel, environmentally friendly, cellulose-based biocomposites, suitable for high-performance applications. Nevertheless, there are limitations restricting the use of cellulose fibers, or nano-sized cellulose as reinforcements and the most important one is the poor compatibility between the hydrophobic polymer matrix and the hydrophilic cellulose fiber.[3] Firstly, this causes difficulties in dispersion of the fiber homogenously in the matrix. Secondly, the poor compatibility gives rise to low interfacial adhesion between the components. Thereby, when the material is subjected to a tensile force, the performance of the material is limited by fiber-pull out rather than fiber-break. Hence, the full potential of the cellulose fiber as reinforcement is not utilized, and in order to do so the compatibility between the hydrophobic matrix and the hydrophilic fiber must be improved. This can be obtained by grafting of a nonpolar polymer from the cellulose surface.[4] The concept of the study is shown in Fig 1. Ring-opening polymerization was used to successfully graft poly(ε-caprolactone) (PCL) directly from the MFC surface; this was confirmed with Fourier Transform Infrared Spectroscopy (FTIR) analysis. The obtained MFC-g-PCL was dispersible in nonpolar solvents, which is in contrast to unmodified MFC that only can be dispersed in polar solvents. By changing the amount of free initiator and monomer added to the system, the amount of polymer on the MFC surface was tailored. Hence, optimization of the graft length for composite applications is possible. Biocomposite films will be prepared from a PCL polymer matrix with different amounts of MFC-g-PCL as reinforcement. The mechanical properties of the films will be analyzed using dynamic mechanical analysis (DMA), and the results will be compared to reference films made from unmodified MFC.
Transcript of Novel Biocomposites from Microfibrillated Cellulose...
Novel Biocomposites from Microfibrillated Cellulose grafted with Poly(ε-caprolactone) – Synthesis and Characterization
Hanna Lönnberg, Linda Fogelström, Lars Berglund, Eva Malmström, and Anders Hult*
Dept. of Fibre- and Polymer Technology, The Royal Institute of Technology, SE-10044 Stockholm, Sweden
KEYWORDS: biocomposites, microfibrillated cellulose, grafting of polymer, ring-opening polymerization, poly(ε-caprolactone), thermal and mechanical properties
INTRODUCTION Environmental concerns have led to a rapid growing interest in replacing traditional petroleum-based technology with more green alternatives. Cellulose, one of the main components in plants, is a biodegradable and renewable recourse. The use of cellulose fibers, instead of traditional fibers such as glass and carbon, offers a way to make more environmental friendly biocomposites. By replacing the traditional fibers with cellulose fibers several benefits are achieved, such as low density, low cost, good specific mechanical properties, reduced tool wear, and biodegradability.[1] Microfibrillated cellulose (MFC) is moderately degraded, nano-sized cellulose, which exhibits unique properties with high modulus and strength, and at the same time a high aspect ratio.[2] These are important properties for development of novel, environmentally friendly, cellulose-based biocomposites, suitable for high-performance applications. Nevertheless, there are limitations restricting the use of cellulose fibers, or nano-sized cellulose as reinforcements and the most important one is the poor compatibility between the hydrophobic polymer matrix and the hydrophilic cellulose fiber.[3] Firstly, this causes difficulties in dispersion of the fiber homogenously in the matrix. Secondly, the poor compatibility gives rise to low interfacial adhesion between the components. Thereby, when the material is subjected to a tensile force, the performance of the material is limited by fiber-pull out rather than fiber-break. Hence, the full potential of the cellulose fiber as reinforcement is not utilized, and in order to do so the compatibility between the hydrophobic matrix and the hydrophilic fiber must be improved. This can be obtained by grafting of a nonpolar polymer from the cellulose surface.[4] The concept of the study is shown in Fig 1. Ring-opening polymerization was used to successfully graft poly(ε-caprolactone) (PCL) directly from the MFC surface; this was confirmed with Fourier Transform Infrared Spectroscopy (FTIR) analysis. The obtained MFC-g-PCL was dispersible in nonpolar solvents, which is in contrast to unmodified MFC that only can be dispersed in polar solvents. By changing the amount of free initiator and monomer added to the system, the amount of polymer on the MFC surface was tailored. Hence, optimization of the graft length for composite applications is possible. Biocomposite films will be prepared from a PCL polymer matrix with different amounts of MFC-g-PCL as reinforcement. The mechanical properties of the films will be analyzed using dynamic mechanical analysis (DMA), and the results will be compared to reference films made from unmodified MFC.
The increased hydrophobicity of the MFC is expected to improve the interfacial adhesion between the components in the biocomposite. Consequently, improved mechanical properties of the novel biocomposites are also anticipated.
Grafting of polymer Mixing with polymer
matrix
MFC MFC-g-PCL Biocomposite
Fig. 1: Conceptual figure – Grafting of poly(ε-caprolactone) from the MFC surface, and subsequent mixing with a polymer matrix to prepare a biocomposite.
REFERENCES
1. Mohanty, A.K., M. Misra, and G. Hinrichsen, Biofibres, biodegradable polymers and biocomposites. An overview. Macromolecular Materials and Engineering, 276/277: p. 1-24, 2000
2. Turbak, A.F., F.W. Snyder, and K.R. Sandberg, Microfibrillated cellulose, a new cellulose product: properties, uses, and commercial potential. Journal of Applied Polymer Science: Applied Polymer Symposium, 37(Proc. Cellul. Conf., 9th, 1982, Part 2): p. 815-27, 1983
3. Samir, M.A.S.A., F. Alloin, and A. Dufresne, Review of Recent Research into Cellulosic Whiskers, Their Properties and Their Application in Nanocomposite Field. Biomacromolecules, 6(2): p. 612-626, 2005
4. Lonnberg, H., et al., Grafting of cellulose fibers with poly(epsilon-caprolactone) and Poly(L-lactic acid) via ring-opening polymerization. Biomacromolecules, 7(7): p. 2178-85, 2006
