Barrier properties melt intercalation

This is a highly polar polymer and crystalline due to the presence of amide linkages. To achieve effective intercalation and exfoliation, the nanoclay has to be modified with some functional polar group. Most commonly, amino acid treatment is done for the nanoclays. Nanocomposites have been prepared using in situ polymerization [85] and melt-intercalation methods [113-117]. Crystallization behavior [118-122], mechanical [123,124], thermal, and barrier properties, and kinetic study [125,126] have been carried out. Nylon-based nanocomposites are now being produced commercially. 

The PLA layered silicate nanocomposites were prepared by adding small amounts of the compatibilizer to form the randomly distributed intercalated silicate layers. Simple melt extmsion of PLA and organically modified montmorillonite lead to better parallel stacking of silicate layers and much stronger flocculation due to hydroxylated edge-edge interactions of silicate layers and consequently improved mechanical and barrier properties, which makes it suitable for food packaging applicatioa Fmther, Bondeson et al. used melt extmsion to fabricate a transparent bio-based nanocomposite of 5 wt% cellulose nanowhiskers (CNW) and cellulose acetate butyrate (CAB), plasticized by triethyl citrate (TEC) (2007). 

As described in Section 11.2.3.3.3, APES can be biodegradable depending on their chemical formulation. Park et al. [351] prepared bionanocomposites of a biodegradable APES prepared by polycondensation of aliphatic glycols (ethylene glycol and 1,4-butanediol) and ahphatic dicarboxylic acids (succinic and adipic acids), TPS, and MMT (Cloisite 30B) via melt intercalation. They found that adding APES to the TPS/Cloisite 30B hybrids led to higher TS and improved barrier properties. 

Layered silicate nanoparticles have also been used to prepare PEN-based nanocomposites through the direct intercalation of PEN polymer chains from the melt into the surface-treated clay. An internal mixer was used and exfoliated silicate layers within a PEN matrix were obtained. Mechanical and barrier properties measnred by dynamic mechanical and permeability analysis showed significant improvanents in the storage modulus and water permeabihty when compared to neat PEN (Wu and Liu, 2005). 

The preparation of PCL nanocomposites by melt blending leads to microcomposites when Cloisite Na is used whereas intercalated structures are obtained with organo-modified clays such as Cloisite 25A and Cloisite 30B. As expected, the mechanical and barrier properties of the conventional microcomposites are in the same range of unfilled PCL. In contrast, all main properties of the material are improved by intercalating polymer chains between silicate sheets. 

As far as Cloisite Na and Cloisite 25A are concerned, the obtained PCL-based nanocomposites present an intercalated structure. For these intercalated nanocomposites prepared by in-situ polymerization, the thermal and barrier properties are similar to those of intercalated nanocomposites obtained by melt blending. In contrast, the exfoliated nanocomposites show a dramatic improvement of the aforementioned properties, as reported by following. 

As expected, all intercalated nanocomposites show very similar "gas barrier" behaviour, whether they have been prepared by melt blending or by in-situ intercalative polymerization. In contrast, the exfoliated samples obtained by in-situ polymerization of e-CL in presence of Cloisite 30B show enhanced barrier properties, as evidenced by determining the zero concentration diffusion coefficient (Do) by microgravimetry (Figure 6). In... 

Aliphatic polyester layered silicate nanocomposites based on poly(e-caprolactone) (PCL) and on plasticized poly(L-lactide) (PLA) have been prepared first by melt blending of the respective polymer matrix with different (organo-modified) montmorillonites. It has been demonstrated that melt blending with organo-modified clay such as Cloisite 20A, 25A or SOB, yields intercalated nanocomposites with the possibility of partial exfoliation. Even at low organoclay content, substantial improvement of thermal stability, gas barrier properties and physical-mechanical performances have been noticed. However, melt blending of natural montmorillonite with PCL or neat (non plasticized) PLA leads to microphase-separated compositions. 

Nanometer-scale composites prepared from layered inorganic materials, especially clay, and polymers have also attracted much attention because of their unique optical, thermal, mechanical, gas barrier, and electrical properties. There are many reports describing polymer-clay nanocomposites. " The clay can be, for example, a sihca or silicate. In such a hybrid composite, weak dipolar and van der Waals forces provide the driving force for interactions between the layers, and they result in galleries being formed. There are three types of clay-polymer composites conventional, intercalated, and exfohated. Three mediods are widely used for the preparation of polymer-clay hybrid nanocomposites intercalation by in situ polymerization, direct intercalation, and polymer melt intercalation. Each of these methods has its advantages and disadvantages. For example, the in situ polymerization works only in tiie... 

Shafiee M, Ramazani SAA, Danaei M. Investigation of the gas barrier properties of PP/clay nanocomposite films with EVA as a compatibiliser prepared by the melt intercalation method. Polym-Plast Technol Eng 2010 49 991-995. 

---