Polymeric bionanocomposites

Polymeric Bionanocomposites as Promising Materials for Controlled Drug Delivery... 

Fu, Y., Li, P, Bu, L. et al (2010) Chemical/biochemical preparation of new polymeric bionanocomposites with enzyme labels immobilized at high load and activity for high-performance electrochemical immunoassay. J. Phys. Chem. C, 114,1472-1480. 

Habibi, Y. Goffin, A.L. Schiltz, N. Duquesne, E. Dubois, R Dufresne, A. Bionanocomposites based on poly(epsilon-caprolactone)-grafted cellulose nanocrystals by ring-opening polymerization. J. Mater. Chem. 2008, 18 (1), 5002-5010. 

Habibi, Y. (2008). Bionanocomposites based on poly( -caprolactone)-grafted cellulose nanociystals by ring-opening polymerization, /. Mater. Che.m.. 18, 5002-5010. 

Habibi Y, Goffin AL, Schiltz N et al (2008) Bionanocomposites based (m poly(epsilgrafted cellulose nanocrystals by ring-opening polymerization. J Mater Chan 18 5002-5010 Hakansson H, Ahlgren P (2005) Acid hydrolysis of some industrials pulps of hydrolysis conditions... 

A layered particle-reinforced bionanocomposite, also known as a layered polymer nanocomposite (LPN), can be classified into three subcategories depending on how the particles are dispersed in the matrix. Intercalated nanocomposites are produced when polymer chains are intercalated between sheets of the layered nanoparticles, whereas exfoliated nanocomposites are obtained when there is separation of individual layers, and flocculated or phase-separated nanocomposites are produced when there is no separation between the layers due to particle-particle interactions. This last class of composites is often named microcomposites as the individual laminas do not separate, thus acting as microparticles dispersed in the polymeric matrix. Their mechanical and physical properties are poorer than exfoliated and intercalated nanocomposites [17, 20, 21, 36, 37]. Figure 11.1 shows a schematic drawing of the structure of layered nanocomposites. 

This is of paramount importance because reinforcement content in bionanocomposites is low and also because high surface area nanoparticles have a natural tendency to agglomerate rather than disperse in the matrix [37, 45, 58, 59, 130], Bionanocomposites can be prepared mostly by solution and melt dispersion, and in situ polymerization [20, 36, 37, 131-134]. 

In situ polymerization is a method of bionanocomposite preparation whereby the nanostructured reinforcement, usually layered clays, is dispersed in a liquid monomer or a monomer dissolved in a suitable solvent for a certain amount of time, allowing monomer molecules to diffuse between the layers. Upon further addition of initiator or exposure of appropriate source of light or heat, the polymerization takes place in situ forming the nanocomposite. 

Bionanocomposites based on PLA and organically modified VMT by in situ in-tercalative polymerization were prepared by Zhang et al. [288]. They concluded that exfoliated composites were obtained and that the bionanocomposites had improved storage and loss modulus, as well as increased glass transition temperature. Tensile tests also showed that the exfoliated nanocomposites are reinforced and toughened by the addition of nanometer-size VMT layers. 

PCL, is an important APES with many potential applications in biomedical and environmental fields [144]. This polymer was the first one to be studied in bionanocomposite when in the early 1990s, GianneUs group from Cornell University (Ithaca, NY, USA) started to work on the elaboration of PCL-based nanocomposites by intercalative polymerization [295]. Since then, a vast number of bionanocomposites have been prepared [87]. Several groups used intercalation, master batches, and in situ polymerization of PCL with clays to produce a variety of nanocomposites as can be seen in Table 11.2. Not only clays, but also various types of nanoreinforcements such as cellulose [296] and StNs [297, 298], chitin [299] nanowhiskers, carbon nanotubes [300, 301], and silica nanoparticles [302] have been used to prepare bionanocomposites with PCL. 

Messersmith and GianneUs [303] developed bionanocomposites of PCL and MMT organically modified with a protonated amino acid to promote delamination/dispersion of the host layers and initiate ring-opening polymerization of s-caprolactone monomer. This resulted in PCL chains that were ionically bound to the siUcate layers (Figure 11.22). Films with a significant reduction... 

In other studies [307, 308], this same group produced bionanocomposites by melt intercalation of PCL and MMT modified by various alkylammonium cations. Depending on whether the ammonium cations contain nonfunctional alkyl chains or chains terminated by carboxylic acid or hydroxyl functions, microcomposites or nanocomposites were produced. The layered silicate PCL nanocomposites exhibited some improvement in mechanical properties and increased thermal stabihty as well as enhanced flame retardancy. The authors concluded that formation of PCL-based nanocomposites, not only depended on the nature of the ammonium cation and its functionaHty, but also on the selected synthetic route, that is, melt intercalation versus in situ intercalative polymerization. 

Morales et al. [323] prepared bionanocomposites of PEA (derived from glycohc acid and 6-aminohexanoic add by in situ polymerization) reinforced with OMMTs. The most dispersed structure was obtained by addition of C25A organoclay. Evaluation of thermal stability and crystallization behavior of these samples showed significant differences between the neat polymer and its nanocomposite with C25A. Isothermal and nonisothermal calorimetric analyses of the polymerization reaction revealed that the kinetics was highly influenced by the presence of the silicate particles. Crystallization of the polymer was observed to occur when the process was isothermally conducted at temperatures lower than 145 °C. In this case, dynamic FTIR spectra and WAXD profiles obtained with synchrotron radiation were essential to study the polymerization kinetics. Clay particles seemed to reduce chain mobility and the Arrhenius preexponential factor. 

PGA, is another biodegradable polymer with applicability in bionanocomposites [372] and, like PVA and PVAc, PGA is readily soluble in water and can be processed by extrusion, injection, and compression molding similarly to other thermoplastics. Murugan et al. [373] produced bionanocomposites of PGA and clay by polymerizing glycolic acid under vacuum in the presence and absence of nanoday which act as a catalyst to the condensation polymerization of PGA. They found that addition of clay improved flame retardancy. 

During the process, clay nanofiUers are initially swollen in the solvent prior to being mixed with bioepoxy matrices. Subsequently, bioepoxy molecules are intercalated into clay interlayers to substitute for solvent molecules that are eventually evaporated. Upon complete solvent removal, intercalated structures are formed in the bionanocomposite system with the aid of a continuous polymerization process. Figure 6.7. 

Table 6.5 Bionanocomposite materials made by in situ polymerization... 

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