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A simple route towards polycarbonate–silica nanocomposite
Advanced Powder Technology 21 (2010) 341–343
Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Rapid Communication
A simple route towards polycarbonate–silica nanocomposite Joseph Lik Hang Chau a,*, Steve Lien-Chung Hsu b, Yi-Ming Chen a, Chih-Chao Yang a, Peter C.F. Hsu c a
Nanopowder and Thin Film Technology Center, ITRI South, Industrial Technology Research Institute, Tainan County, Taiwan Department of Materials Science and Engineering, National Cheng Kung University, Tainan City, Taiwan c Division of Mechanical Technology Development, Wistron Corporation, Taipei County, Taiwan b
a r t i c l e
i n f o
Article history: Received 17 December 2009 Received in revised form 5 February 2010 Accepted 12 February 2010
Keywords: Nanocomposite Nanopowder Silica Polycarbonate Hardness
a b s t r a c t This work reports the preparation of polycarbonate–silica nanocomposite by simple one-step injection moulding process. Silica nanopowder was first functionalized with a silane coupling agent, (3-methacryloxypropyl)trimethoxysilane (MPS). Polycarbonate pellets mixed with 5 wt% functionalized-silica nanopowders were then compounded by using a Brabender counter-rotating twin screw compounder followed by subsequent injection molding process. The distribution of silica was examined using transmission electron microscopy (TEM). The FT-IR spectra were used to investigate the MPS-modified SiO2 nanopowders. The thermal properties of the nanocomposite were studied by differential scanning calorimeter (DSC). Pencil hardness is increased from B to HB with the incorporation of 5 wt% silica nanopowder. Ó 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction Incorporating nanoparticles or nanofillers into polymer matrix have attracted increasing attention recently. Among the nanocomposite materials, silica-polymer nanocomposite is the most widely studied due to the potential applications in protective coatings, reinforced plastics and optical devices [1–3]. The distinctive properties of these nanocomposites can be greatly affected by both the dispersion degree of nanoparticles in the polymer matrix and the interfacial interaction between the inorganic and organic matrix [4]. Surface functionalization of nanoparticles thus plays a critical role in these issues. Many approaches were developed to prepare polymer-silica nanocomposite in recent years such as miniemulsion polymerization by using methyl methacrylate/butyl acrylate mixture containing silica nanoparticles [5]. The silica nanoparticles in the nanocomposite was usually prepared from alkoxysilanes [6] or colloidal silica [7] through different chemical means. Nanocomposites are then formed by carrying out polymerization in the presence of surface modified-silica nanoparticles. Kim et al. reported the surface modification of silica nanoparticles with methyl methacrylate by UV-induced graft polymerization reaction [8]. The resulting nanocomposites were fabricated without homopolymerization of the monomer. Yu et al. synthesized surface modified-silica particles and copolymerized the modified-silica with methyl methacrylate (MMA) monomers [9]. Another approach that frequently used is the sol–gel process coupled with polymerization to generate organ* Corresponding author. Tel.: +886 6 3847275; fax: +886 6 3847288. E-mail address: [email protected] (J.L.H. Chau).
ic–inorganic hybrid materials [10]. However, the removal of solvent and complex polymerization process during the reaction hindered the industrial applications of these nanocomposites. Hard-coating is a mature technique to enhance the surface hardness of different materials. However, the major drawback falls on the two-step processing conditions. After molding the desired object, dip-coating or spin-coating with harder layer is performed in order to increase the mechanical properties of the surface. This is time consuming and more expensive than using one-step process. The objective of this work is to find a simple, cheaper and one-stage direct process to enhance the mechanical properties of polycarbonate, which is the main component of notebook case commonly used in computer notebook industries. In this work, silica nanopowder was functionalized with a silane coupling agent, (3-methacryloxypropyl)trimethoxysilane (MPS). The surface modified-silica nanopowder was then directly mixed with the polycarbonate pellets and compounded by using a Brabender counter-rotating twin screw compounder followed by subsequent injection molding process. In this process, because the silica nanoparticle is not in colloidal form, removal of solvent is not necessary. Nanocomposite with improved hardness can be formed in simple one-stage process. 2. Experimental 2.1. Surface functionalization of silica nanopowders Silica nanopowders were purchased from UniRegion Bio-Tech company (UR-ISIL001, average primary particle size 40 nm, pur-
0921-8831/$ - see front matter Ó 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2010.02.005
342
J.L.H. Chau et al. / Advanced Powder Technology 21 (2010) 341–343
T (%)
MPS
SiO2
MPS-SiO2 -CH3 or =CH2
4000
3000
C=O
Si-O-Si
2000
1000 -1
Wavenumber (cm ) Fig. 1. FT-IR spectra of pure MPS, commercial silica nanopowder and MPS modified-silica nanopowder.
Fig. 2. SEM micrograph of the functionalized-silica nanopowders.
ity >99.9%). (3-methacryloxypropyl)trimethoxysilane (MPS) is used to functionalize the commercial silica nanopowders. The functional group –Si(OCH3)3 can be chemically bonded to the surface of silica nanopowder and the carbon–carbon double bond can be reacted with polymer during the injection moulding process. In a typical preparation, 1500 ml of tetrahydrofuran and 117 g of MPS surface modifying agent was mixed well. About 250 g of silica nanopowders was then added into the mixture. The resulting suspension was ultrasonically stirred for 2 h. White precipitate was formed after sedimentation at ambient environment. The surface modified-silica nanopowders were then washed with tetrahydrofuran (THF) several times to remove excess MPS and dried at ambient environment for further processing. The dried silica nanopowders can also be stored for long time without the problem of stabilization. Scanning electron microscopy (SEM, JEOL-5400) was used to observe the morphology of the functionalized-silica nanopowders. 2.2. Compounding and injection molding to form nanocomposite Polycarbonate pellets with 5 wt% of dried surface modified-silica nanopowders were compounded by using a Brabender counter-
Fig. 3. (a) TEM micrograph of polycarbonate–silica nanocomposite containing 5 wt% of silica, (b) higher magnification TEM micrograph of polycarbonate–silica nanocomposite containing 5 wt% of silica.
rotating twin screw compounder. The nanocomposite extrudates were granulated for subsequent injection molding. Sample of size 4 12 0.3 cm3 were injection molded from silica–polycarbonate blends prepared using a reciprocating-screw machine. TEM images were taken from microtome ultrathin sections of the molded nanocomposite using a transmission electron microscope (JEOL2000EX). The glass transition temperature (Tg) was evaluated by using differential scanning calorimetry (Thermal analysis DSCQ10). The IR spectra were recorded on a Jasco 460 FTIR spectrometer. The hardness was measured by using a pencil test. 3. Results and discussion The silica nanopowders can be grafted with many allyl functional groups and act as cross-linking agent with the polymer matrix. Dried surface functionalized-silica nanopowders can be incorporated directly into polymer matrix using compounding and injection molding process. This process enables the industrial users to manipulate the silica content of the nanocomposites according to their product specifications. Modification of molding
J.L.H. Chau et al. / Advanced Powder Technology 21 (2010) 341–343
machinery or molding process is not necessary. The dried surface modified-nanopowders were mixed directly with polymer pellets during the compounding stage and can significantly simplify the process for preparing nanocomposite materials. The FT-IR spectra were used to investigate the MPS-modified SiO2 particles. From Fig. 1, the absorption peak at 2945 cm 1 was attributed to the absorption of the alkyl chain and the peak around 1720 cm 1 was the C@O bond vibration. The MPS-modified SiO2 with these absorption peaks can be clearly distinguished from the unmodified SiO2. Fig. 2 shows the SEM micrograph of the functionalized-silica nanopowders. The average particle size of silica is about 40 nm. The dried surface modified-silica nanopowders can be easily dispersed in THF and remain stable without aggregation or sedimentation after one month. Fig. 3(a) shows the typical TEM micrograph of polycarbonate–silica nanocomposite containing 5 wt% of silica. From the TEM analysis (Fig. 3(b)), the primary silica nanopowders aggregate into some small nano-clusters and these nano-clusters dispersed well in the polymer matrix. However, well dispersion of primary silica particles inside the polymer matrix was not observed. The surface functionalized-silica nanopowders will form aggregates after the drying process. It is expected that the silica nanopowders aggregates cannot be dispersed into primary nanoparticles during the short time interval in the compounding process. The thermal property of the nanocomposite was investigated by DSC analysis. The glass transition temperature of the polycarbonate was found to be 110 °C, while with the addition of 5 wt% silica nanopowder increases the Tg of the nanocomposite to 115 °C. The DSC results showed that the incorporation of silica nanopowders enhanced the thermal stability of the polycarbonate–silica nanocomposite. The polymer chain motion was thus restricted by the interfacial-particle interactions between the surface functionalized-silica nanopowders and the polymer molecules. The polycarbonate have hardness grade of B and the hardness grade of
343
polycarbonate–silica nanocomposite with 5 wt% surface modified-silica content can be increased to HB. Although commercial silica nanopowder (5 wt%) without surface modification can be incorporated directly into polymer matrix using compounding and injection molding process, this nanocomposite only have hardness grade of B, indicating the surface functionalization of silica nanopowders plays an important role as cross-linking agent with the polymer matrix. 4. Conclusion Surface functionalized-silica nanopowders can be directly compounded with polycarbonate pellets. Polycarbonate–silica nanocomposite can be formed and produced at large-scale by onestage injection molding process. Hardness of the polycarbonate can be improved by directly incorporation of these silica nanopowders into the polymer matrix without the need of performing subsequent surface hard-coating process. Addition of 5 wt% silica nanopowder can increase the glass transition temperature and hardness of the polycarbonate. Other types of nanocomposites can also be potentially prepared in large-scale production by using the simple process described in this work. References [1] A. Erashad-Langroudi, C. Mai, G. Vigier, R. Vassoille, J. Appl. Polym. Sci. 65 (1997) 2387. [2] L.H. Lee, W.C. Chen, Chem. Mater. 13 (2001) 1137. [3] M. Yashida, P.N. Prasad, Chem. Mater. 8 (1996) 235. [4] M.N. Xiong, L.M. Wu, S.X. Zhou, B. You B, Polym. Int. 51 (2002) 693. [5] D.M. Qi, Y.Z. Bao, Z.X. Weng, Z.M. Huang, Polymer 47 (2006) 4622. [6] B.K. Coltrain, C.J.T. Landry, J.M. O’Reilly, A.M. Chamberlain, G.A. Rakes, J.S. Sedita, L.W. Kelts, M.R. Landry, V.K. Long, Chem. Mater. 5 (1993) 1445. [7] J.M. Jethmalani, W.T. Ford, G. Beaucage, Langmuir 13 (1997) 3338. [8] S.Y. Kim, E.H. Kim, S.S. Kim, W.S. Kim, J. Colloid Interface Sci. 292 (2005) 93. [9] Y.Y. Yu, C.Y. Chen, W.C. Chen, Polymer 44 (2003) 593. [10] J.Z. Ma, J. Hu, Z.J. Zhang, Eur. Polym. J. 43 (2007) 4169.
Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Rapid Communication
A simple route towards polycarbonate–silica nanocomposite Joseph Lik Hang Chau a,*, Steve Lien-Chung Hsu b, Yi-Ming Chen a, Chih-Chao Yang a, Peter C.F. Hsu c a
Nanopowder and Thin Film Technology Center, ITRI South, Industrial Technology Research Institute, Tainan County, Taiwan Department of Materials Science and Engineering, National Cheng Kung University, Tainan City, Taiwan c Division of Mechanical Technology Development, Wistron Corporation, Taipei County, Taiwan b
a r t i c l e
i n f o
Article history: Received 17 December 2009 Received in revised form 5 February 2010 Accepted 12 February 2010
Keywords: Nanocomposite Nanopowder Silica Polycarbonate Hardness
a b s t r a c t This work reports the preparation of polycarbonate–silica nanocomposite by simple one-step injection moulding process. Silica nanopowder was first functionalized with a silane coupling agent, (3-methacryloxypropyl)trimethoxysilane (MPS). Polycarbonate pellets mixed with 5 wt% functionalized-silica nanopowders were then compounded by using a Brabender counter-rotating twin screw compounder followed by subsequent injection molding process. The distribution of silica was examined using transmission electron microscopy (TEM). The FT-IR spectra were used to investigate the MPS-modified SiO2 nanopowders. The thermal properties of the nanocomposite were studied by differential scanning calorimeter (DSC). Pencil hardness is increased from B to HB with the incorporation of 5 wt% silica nanopowder. Ó 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction Incorporating nanoparticles or nanofillers into polymer matrix have attracted increasing attention recently. Among the nanocomposite materials, silica-polymer nanocomposite is the most widely studied due to the potential applications in protective coatings, reinforced plastics and optical devices [1–3]. The distinctive properties of these nanocomposites can be greatly affected by both the dispersion degree of nanoparticles in the polymer matrix and the interfacial interaction between the inorganic and organic matrix [4]. Surface functionalization of nanoparticles thus plays a critical role in these issues. Many approaches were developed to prepare polymer-silica nanocomposite in recent years such as miniemulsion polymerization by using methyl methacrylate/butyl acrylate mixture containing silica nanoparticles [5]. The silica nanoparticles in the nanocomposite was usually prepared from alkoxysilanes [6] or colloidal silica [7] through different chemical means. Nanocomposites are then formed by carrying out polymerization in the presence of surface modified-silica nanoparticles. Kim et al. reported the surface modification of silica nanoparticles with methyl methacrylate by UV-induced graft polymerization reaction [8]. The resulting nanocomposites were fabricated without homopolymerization of the monomer. Yu et al. synthesized surface modified-silica particles and copolymerized the modified-silica with methyl methacrylate (MMA) monomers [9]. Another approach that frequently used is the sol–gel process coupled with polymerization to generate organ* Corresponding author. Tel.: +886 6 3847275; fax: +886 6 3847288. E-mail address: [email protected] (J.L.H. Chau).
ic–inorganic hybrid materials [10]. However, the removal of solvent and complex polymerization process during the reaction hindered the industrial applications of these nanocomposites. Hard-coating is a mature technique to enhance the surface hardness of different materials. However, the major drawback falls on the two-step processing conditions. After molding the desired object, dip-coating or spin-coating with harder layer is performed in order to increase the mechanical properties of the surface. This is time consuming and more expensive than using one-step process. The objective of this work is to find a simple, cheaper and one-stage direct process to enhance the mechanical properties of polycarbonate, which is the main component of notebook case commonly used in computer notebook industries. In this work, silica nanopowder was functionalized with a silane coupling agent, (3-methacryloxypropyl)trimethoxysilane (MPS). The surface modified-silica nanopowder was then directly mixed with the polycarbonate pellets and compounded by using a Brabender counter-rotating twin screw compounder followed by subsequent injection molding process. In this process, because the silica nanoparticle is not in colloidal form, removal of solvent is not necessary. Nanocomposite with improved hardness can be formed in simple one-stage process. 2. Experimental 2.1. Surface functionalization of silica nanopowders Silica nanopowders were purchased from UniRegion Bio-Tech company (UR-ISIL001, average primary particle size 40 nm, pur-
0921-8831/$ - see front matter Ó 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2010.02.005
342
J.L.H. Chau et al. / Advanced Powder Technology 21 (2010) 341–343
T (%)
MPS
SiO2
MPS-SiO2 -CH3 or =CH2
4000
3000
C=O
Si-O-Si
2000
1000 -1
Wavenumber (cm ) Fig. 1. FT-IR spectra of pure MPS, commercial silica nanopowder and MPS modified-silica nanopowder.
Fig. 2. SEM micrograph of the functionalized-silica nanopowders.
ity >99.9%). (3-methacryloxypropyl)trimethoxysilane (MPS) is used to functionalize the commercial silica nanopowders. The functional group –Si(OCH3)3 can be chemically bonded to the surface of silica nanopowder and the carbon–carbon double bond can be reacted with polymer during the injection moulding process. In a typical preparation, 1500 ml of tetrahydrofuran and 117 g of MPS surface modifying agent was mixed well. About 250 g of silica nanopowders was then added into the mixture. The resulting suspension was ultrasonically stirred for 2 h. White precipitate was formed after sedimentation at ambient environment. The surface modified-silica nanopowders were then washed with tetrahydrofuran (THF) several times to remove excess MPS and dried at ambient environment for further processing. The dried silica nanopowders can also be stored for long time without the problem of stabilization. Scanning electron microscopy (SEM, JEOL-5400) was used to observe the morphology of the functionalized-silica nanopowders. 2.2. Compounding and injection molding to form nanocomposite Polycarbonate pellets with 5 wt% of dried surface modified-silica nanopowders were compounded by using a Brabender counter-
Fig. 3. (a) TEM micrograph of polycarbonate–silica nanocomposite containing 5 wt% of silica, (b) higher magnification TEM micrograph of polycarbonate–silica nanocomposite containing 5 wt% of silica.
rotating twin screw compounder. The nanocomposite extrudates were granulated for subsequent injection molding. Sample of size 4 12 0.3 cm3 were injection molded from silica–polycarbonate blends prepared using a reciprocating-screw machine. TEM images were taken from microtome ultrathin sections of the molded nanocomposite using a transmission electron microscope (JEOL2000EX). The glass transition temperature (Tg) was evaluated by using differential scanning calorimetry (Thermal analysis DSCQ10). The IR spectra were recorded on a Jasco 460 FTIR spectrometer. The hardness was measured by using a pencil test. 3. Results and discussion The silica nanopowders can be grafted with many allyl functional groups and act as cross-linking agent with the polymer matrix. Dried surface functionalized-silica nanopowders can be incorporated directly into polymer matrix using compounding and injection molding process. This process enables the industrial users to manipulate the silica content of the nanocomposites according to their product specifications. Modification of molding
J.L.H. Chau et al. / Advanced Powder Technology 21 (2010) 341–343
machinery or molding process is not necessary. The dried surface modified-nanopowders were mixed directly with polymer pellets during the compounding stage and can significantly simplify the process for preparing nanocomposite materials. The FT-IR spectra were used to investigate the MPS-modified SiO2 particles. From Fig. 1, the absorption peak at 2945 cm 1 was attributed to the absorption of the alkyl chain and the peak around 1720 cm 1 was the C@O bond vibration. The MPS-modified SiO2 with these absorption peaks can be clearly distinguished from the unmodified SiO2. Fig. 2 shows the SEM micrograph of the functionalized-silica nanopowders. The average particle size of silica is about 40 nm. The dried surface modified-silica nanopowders can be easily dispersed in THF and remain stable without aggregation or sedimentation after one month. Fig. 3(a) shows the typical TEM micrograph of polycarbonate–silica nanocomposite containing 5 wt% of silica. From the TEM analysis (Fig. 3(b)), the primary silica nanopowders aggregate into some small nano-clusters and these nano-clusters dispersed well in the polymer matrix. However, well dispersion of primary silica particles inside the polymer matrix was not observed. The surface functionalized-silica nanopowders will form aggregates after the drying process. It is expected that the silica nanopowders aggregates cannot be dispersed into primary nanoparticles during the short time interval in the compounding process. The thermal property of the nanocomposite was investigated by DSC analysis. The glass transition temperature of the polycarbonate was found to be 110 °C, while with the addition of 5 wt% silica nanopowder increases the Tg of the nanocomposite to 115 °C. The DSC results showed that the incorporation of silica nanopowders enhanced the thermal stability of the polycarbonate–silica nanocomposite. The polymer chain motion was thus restricted by the interfacial-particle interactions between the surface functionalized-silica nanopowders and the polymer molecules. The polycarbonate have hardness grade of B and the hardness grade of
343
polycarbonate–silica nanocomposite with 5 wt% surface modified-silica content can be increased to HB. Although commercial silica nanopowder (5 wt%) without surface modification can be incorporated directly into polymer matrix using compounding and injection molding process, this nanocomposite only have hardness grade of B, indicating the surface functionalization of silica nanopowders plays an important role as cross-linking agent with the polymer matrix. 4. Conclusion Surface functionalized-silica nanopowders can be directly compounded with polycarbonate pellets. Polycarbonate–silica nanocomposite can be formed and produced at large-scale by onestage injection molding process. Hardness of the polycarbonate can be improved by directly incorporation of these silica nanopowders into the polymer matrix without the need of performing subsequent surface hard-coating process. Addition of 5 wt% silica nanopowder can increase the glass transition temperature and hardness of the polycarbonate. Other types of nanocomposites can also be potentially prepared in large-scale production by using the simple process described in this work. References [1] A. Erashad-Langroudi, C. Mai, G. Vigier, R. Vassoille, J. Appl. Polym. Sci. 65 (1997) 2387. [2] L.H. Lee, W.C. Chen, Chem. Mater. 13 (2001) 1137. [3] M. Yashida, P.N. Prasad, Chem. Mater. 8 (1996) 235. [4] M.N. Xiong, L.M. Wu, S.X. Zhou, B. You B, Polym. Int. 51 (2002) 693. [5] D.M. Qi, Y.Z. Bao, Z.X. Weng, Z.M. Huang, Polymer 47 (2006) 4622. [6] B.K. Coltrain, C.J.T. Landry, J.M. O’Reilly, A.M. Chamberlain, G.A. Rakes, J.S. Sedita, L.W. Kelts, M.R. Landry, V.K. Long, Chem. Mater. 5 (1993) 1445. [7] J.M. Jethmalani, W.T. Ford, G. Beaucage, Langmuir 13 (1997) 3338. [8] S.Y. Kim, E.H. Kim, S.S. Kim, W.S. Kim, J. Colloid Interface Sci. 292 (2005) 93. [9] Y.Y. Yu, C.Y. Chen, W.C. Chen, Polymer 44 (2003) 593. [10] J.Z. Ma, J. Hu, Z.J. Zhang, Eur. Polym. J. 43 (2007) 4169.