Surface Modification of Montmorillonite
Due to their small size, surface interactions, such as hydrogen bonding become magnified. What this implies is that the particles tend to agglomerate and dispersion in polymer matrix is difficult, even in polymers that should be relatively compatible. Using compatibilization agents that will bond to the montmorillonite surface & also interact with the polymer resin to form a more miscible system solves the problem. The process of compatibilization of montmorillonite is the job of companies like Nanocor. Once compatible, the particles can be dispersed into the polymer matrix through a process called Exfoliation. Exfoliation can be done by in-situ reactor polymerization or through melt compounding.
Recently, layered silicate based nanocomposites have found a lot of attention as a simple and cost effective method to enhance polymer properties by the addition of a small amount of suitable designed fillers (organoclays), leading to the creation of composite materials where the reinforcing particles are distributed in the polymeric matrix at the nanometer level. Depending on the nature of the filler distribution within the matrix, the morphology of the generated nanocomposites can evolve from the so-called intercalated nanocomposites with a regular alternation of the layered silicates and polymer monolayers to the exfoliated (delaminated) type of nanocomposites where the layered silicates are randomly and homogeneously distributed within the polymer matrix (figure 1).
The easiest and economic most interested way to produce these types of materials is kneading the polymer in the molten state with a layered silicate such as montmorillonite, usually modified organophilic by exchanging the native Na+ interlayer cation with an alkyl ammonium cation. A large number of polymer matrices have successfully been used for the formation of nanocomposites by this technique, such as PS, PA, EVA, EVOH or SIR. However, non-polar polymers like polyolefins (PE or PP) cannot easily form nanocomposites by this method due to fundamental thermodynamic laws, which demand strong polar interactions between polymers and organoclays for a nanocomposites formation.
Interest of Nanocomposites to plastics industry
Nanocomposites are of great interest to the global plastics markets. Polymer compounds containing only low levels (mainly 5 weight-%) of organoclays can be used for automotive applications), barrier packaging films and improved flame retardant wire & cable jackets and many other applications.
The optimism linked to organoclays has continuously increased since the industry started research investigations since 4-6 years ago. But often it is difficult for the industry to transfer this new class of nanocomposites to real end products because industrial applications must be cost-effective and the relative high prices of organoclays compared to traditional filler prices can hinder real applications. Few years ago some early application development programs have been stopped for cost reasons.
Supplier & Trade name |
Matrix Resin |
Nano-filler |
Target Market |
| Bayer AG (Durethan LPDU) |
Nylon 6 |
Organo-clay |
Barrier films |
| Clariant |
PP |
Organo-clay |
Packaging |
| Creanova (Vestamid) |
Nylon 12 |
Nano-tubes |
Electrically conductive |
| GE Plastics (Noryl GTX) |
PPO/Nylon |
Nano-tubes |
Automotive painted parts |
| Honeywell (Aegis) |
Nylon 6 |
Organo-clay |
Multi-purpose |
| Barrier Nylon |
Organo-clay |
Bottles and Film |
| Hyperion |
PETG, PBT, PPS, PC, PP |
Nano-tubes |
Electrically conductive |
| Kabelwerk Eupen of Belgium |
EVA |
Organo-clay |
Wire & Cable |
| Nanocor (Imperm) |
Nylon 6 |
Organo-clay |
Multi-purpose |
| PP |
Organo-clay |
Molding |
| Nylon MDX6 |
Organo-clay |
PET beer bottles |
| Polymeric Supply |
Unsaturated polyester |
Organo-clay |
Marine transportation |
| RTP |
Nylon 6, PP |
Organo-clay |
Multi-purpose, Electrically conductive |
| Showa Denko (Systemer) |
Nylon 6 |
Clay, Mica |
Flame Retardant |
| Acetal |
Clay, Mica |
Multi-purpose |
| Ube (Ecobesta) |
Nylon 6, 12 |
Organo-clay |
Multi-purpose |
| Nylon 6, 66 |
Organo-clay |
Auto-fuel systems |
| Unitika |
Nylon 6 |
Organo-clay |
Multi-purpose |
| Yantai Haili Ind. & Commerce of China |
UHMWPE |
Organo-clay |
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Table 1: Partial Listing of Nanocomposite Suppliers
Source: Bins & Associates, Sheboygan, Wis., Report on the prospects for nanocomposites |
Such steps included an automotive timing-belt cover based on nylon 6 nanocomposites from Japan's Unitika and an automotive mirror housing of conductive PPO/nylon alloy from GE Plastics. But the research for nanocomposites applications by the plastics industry is unbroken. Nanocomposites can improve polymers' stiffness, enhance applications for higher temperature classes and show improved properties like dimensional stability, gas barrier improvements, increased electrical conductivity and flame retardancy.
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