What color are nanocomposites?
Nanocomposite color will vary depending on the resin system and the chemical treatment of the clay. Because the natural montmorillonite, Cloisite® Na+, is off-white or light tan colored, the nanocomposite will also at least be off white.  Examples of color variation that we have observed are as follows:

Are nanocomposites clear?
There is not a simple yes or no answer to this question. The particle size of montmorillonite is less than the wavelength of visible light, so they can be clear. Our experience making an injected molded part or a sheet from an opaque nanocomposite pellets, is the finished article will be opaque or hazy. Thin films we have made, even from an opaque pellet, are clear. Montmorillonite is an effective nucleating agent and the resulting nature of the crystalline polymer in the film may enable more clarity to the film.

What is the thermal stability of the organoclay?

The thermal stability of the organoclay is determined by the thermal stability of the onium ion treatment. The TGA curve for Cloisite® 20A and Cloisite® 15A is available (TGA figure). These results show the onset of decomposition begins above 200°C for the onium ion on montmorillonite. However, the onset temperature does not consider the kinetic of decomposition. We do not have data on the kinetics of the onium ion decomposition.
Taking into consideration of the thermal stability of the organoclay, extrusion is still an acceptable process to make many nanocomposites. Physical property results have been presented, tensile modulus as an example,(Tensile Modulus figure) comparing PA6 nanocomposite prepared by the in situ and melt blended process.  After normalization for mineral content, the modulus results are comparable. Significant decomposition of the onium ion on montmorillonite would plasticize the PA6 nanocomposite yielding a difference in modulus of melt blended and in situ polymerized PA6 nanocomposite, but the modulus is the same.

What Cloisite® nanoclay is recommended for various plastics?

The recommendations are made based on in-house evaluations. Complete exfoliation is not realized making every nanocomposite.  Also see FAQ 5 on delamination and dispersion.

There is not enough in-house data to make further recommendations for other resins. The structure of the chemical treatment of the various Cloisite® is shown in the Technical Data Sheet. The structures are provided to allow you to use your judgement in selecting samples that contain the chemical treatment that is the most compatible with your resin of interest.

How can I delaminate and disperse (exfoliate) Cloisite® nanoclays?

A. Thermosets:
It is assumed the Cloisite® will be added to a liquid component of the thermoset. Below are some general guidelines for dispersing an organoclay in a liquid. Other processing techniques can be used.

High shear mixing is required. As an example, mixing can be done using a Cowles Dissolver, a round blade with teeth at about 1/3 the tank diameter, turning at high rpm with a tip speed of ~65 feet per second.  For a five inch blade this is 1000-3000 rpm. There should be baffles in the tank.  We try to ensure a good vortex is accomplished.

There are literature reports that for epoxy resins increasing the temperature aids in exfoliation. Temperature of 110°C>90°C >60°C. There is also literature recommending cryogenic mixing.

Compatibility of the liquid with the organoclay is critical. Dispersion of the product could be accomplished at low shear rates if the compatibility is good and enough time is allowed. More time allows more energy, and eventually the clay could disperse. If not compatible, only excessive grinding (high impact with the clay particle) will disperse the clay particle. There can be a difference in what appears to be good dispersion and exfoliation. Good dispersion will not show specks in a draw down test such as in a Hegman Grind Test, but the platelets of the clay do not have to be exfoliated to be dispersed.

 We mix in water having a viscosity of 1 cps. Of course, the viscosity increases as the clay disperses and too much viscosity can slow the dispersion, but some viscosity can help impart the energy to the clay.  Adding clay to only a portion of the liquid dispersant will help build more viscosity and possibly improve dispersion and exfoliation.

Polar activators can also be used to improve exfoliation. Polar activators are polar solvents like low molecular weight alcohols or propylene carbonate. A good starting concentration of polar activator to add is 30 weight percent based upon the weight of the organoclay. The polar activator should be added after the organoclay dispersion process has been started.

B. Thermoplastics:
Cloisite® can be delaminated and dispersed into a thermoplastic by a variety of melting mixing/shearing equipment: extruder; bowl mixer; continuous mixer; two-roll mill, Buss Kneader, etc. The one type of mixing equipment we did not have success with in achieving exfoliation with PA6 and Cloisite® 30B was a single screw extruder.  The remaining comments will be directed at extrusion.

Little information has been published teaching how to make a dispersed and delaminated nanocomposite by melt blending. We have done studies looking at different types of extruders, various screw designs and different process conditions using a specific screw configuration. Varying the process condition does have an affect on delamination and dispersion when making a nanocomposite, as is true when compounding most other types of products. We have much evidence that achieving good delamination and dispersion is dependent upon both the choice of the organoclay and the process conditions.

1. A. Key background points:
   • A nominal sized Cloisite® particle of 8 microns contains over 1,000,000 platelets.
   • The improved properties of nanocomposites depend on the high aspect ratio and surface area of the individual platelets of montmorillonite (MMT).
   • Both the compatibility of the clay chemical treatment with the resin matrix and the melt blending conditions determine the degree of delamination and dispersion. The primary controlling factor of the two is compatibility.
2. The delaminating and dispersion mechanism is proposed to be. (Dispersion Mechanism Figures)
   • The MMT particles shear apart giving tactoids or polymer intercalated MMT.
   • Intercalated MMT in stacks about 100-150nm high disperse when polymer enters the galleries of the clay pushing platelets apart which eventually allows the platelets to peel off the intercalated MMT stack.
   • The peeling takes residence time, not high shear intensity. Increased mean residence time increases delamination and dispersion, but increased shear intensity can decrease delamination and dispersion.
   • Lowering the temperature of the extrusion as much as possible after the resin is melted with help increase shear stress and enhance platelet peeling if there is adequate compatibility.
   • The more compatible the clay chemical treatment and the resin matrix, the faster delamination and dispersion take place.
   • When there is poor compatibility tactoids are dispersed in the polymer matrix yielding a microcomposite.
3. We have not been able to make a single screw extruder work, and recommend the use of a twin screw extruder.
4. Feed the polymer first, and then feed the organoclay into the molten polymer.
5. Pre-blending then adding the resin and the clay together can be done, but may lead to clay particles being compacted and not delaminating.
6. Feeding downstream into the top of the extruder is better than using a side feeder to minimize clay compaction.
7. The downstream clay feeder should be sized to deliver the clay in a smooth stream.
8. The screw configuration used should take into account the proposed delamination and dispersion mechanism.  
9. In our screw design studies, some process parameters were held constant. They need to be optimized, but are a good starting point. 
   • In the MMT mixing part of the screw, we kept the barrel temperature near the melting point of the resin. The die temperature was raised ~5°C.
   • The extruder had a screw speed limit of 500rpm, and we ran 200-300 rpm.
   • On our ZSK-25 we do screening work with a screw speed of 500 rpm.
   • For clay screening evaluations on our ZSK-25 in olefins we run at 18.2kg/hr although we have made well exfoliated PA6 nanocomposites at 50kg/hr.
10. Use of vacuum is advised as air is given off when the MMT delaminates and disperses.

Polyethylene and Polypropylene Nanocomposites

• We recommend the use of Cloisite® 20A  or Cloisite® 15A.
• Additional compatibilization is required to make a polyolefin nanocomposite.
• Maleated polyolefins are probably the best co-compatibilizers known at this time.
• The higher the concentration of maleated polyolefin used, the better the exfoliation and delamination.
• Most of our studies have been with PP. The %MA in the compatibilizer should be in the range of 0.7-1.3%MA. If higher %MA is used, it is important the MAPP and PP be compatible.
• A masterbatch can be used to make a nanocomposite.  TEM micrographs showed the platelets were very crowded together.
• The masterbatch can be let down with a single-screw or twin-screw extruder.  The single–screw extruder had a high intensity mix-head just before the die.
•  We do not recommend the use of a single-screw extruder to let a masterbatch down for a film application where improved barrier is the desired application.

Polyamide Nanocomposites

• We recommend the use of Cloisite® 93A or Cloisite® 30B.
• A variety of polyamides have been made into nanocomposites with these organoclays.
• A good PA6/Cloisite® 30B nanocomposite will be slightly amber in color and transparent, especially at extruder die.
• Process conditions can be varied to optimize process conditions using Cloisite® 30B/PA6 monitoring the extrudate at the die for transparency.

Should I dry my Cloisite® nanoclay before making a nanocomposite?

There is not a simple answer to that question and often the best way to determine an answer is to run some comparative experiments. Clay agglomeration during extruder processing is minimized by drying the Cloisite® (montmorillonite is a great desiccant and will have residual moisture unless that moisture is removed and then care needs to be taken to prevent moisture from being reabsorbed (Moisture Uptake Figure). Clay agglomerates can lead to surface defects in injection molded parts. Clay agglomerates can reduce impact strength.  The appearance of gels or unmelts in nanocomposite film can be attributed to clay agglomeration. One should also refer to question 5 for the affect of processing on nanoclay agglomeration.

What is CEC?

CEC is the cation exchange capacity of the montmorillonite clay. The CEC can be determined by titration by using an ammonium acetate method. (Titration Method). The CEC is a measure of the amount of cations available on the montmorillonite clay. Typically the cation on natural montmorillonite is Na+ or Ca++. These cations can be exchanged with an onium ion to make an organoclay by an ion exchange reaction. To make an organoclay at stoichiometry one equivalent of onium ion is exchanged with one equivalent of cation on the clay. The ion exchange does not have to be run at stoichiometry as the clay can be under or over exchanged.

How can I prepare an organoclay?

Cloisite® Na+ should be dispersed in water at a solids level below 7% using high shear. The CEC of Cloisite® Na+ is 92meq/100g clay so to make a clay at the CEC, 92meq of quat or onium ion should be added to the slurry. (The ion exchange can be done at room temperature, but would recommend running the reaction at a higher temperature, around 60°C. The reaction mixture will become quite viscous so an overhead stirrer is more effective to use for mixing than a magnetic stir bar.) Stir the reaction mixture for about an hour then filter to isolate the organoclay. Wash the organoclay with water and dry the clay. The drying can be done in an oven at about 80°C. There are a variety of ways to grind the clay to a finer particle size, but some simple ways are to use a coffee mill or food processor. A sieve can be used to remove large particles which can be milled again.

Is there a test to predict compatibility of Cloisite® nanoclays?

We are not aware of a simple test to predict which Cloisite® is compatible with different polymers and rubbers. A swelling test can be used for liquids as an initial screen. A general procedure is to add 0.1g of Cloisite® nanoclay to 10cc of a liquid in a 10cc graduated cylinder. Monitor the rate of settling and let the mixture sit for about 24 hours then measure the volume of Cloisite® in the bottom of the graduated cylinder. More detailed information can be obtained by using high shear to disperse the Cloisite® in a liquid and measuring the viscosity at three different shear rates. The higher viscosity result indicates a higher degree of network built (usually associated with a higher degree of exfoliation) when comparing different Cloisites® in a liquid.

What is the difference in, bentonite, smectite, montmorillonite and Cloisite® Na+ nanoclay?

• Bentonite is the rock or ore that contains the clay mineral montmorillonite.
• Smectite is a clay mineral group characterized as an expanding clay mineral which includes the clay minerals vermiculite, sauconite, saponite, nontronite and montmorillonite.
• Montmorillonite is a clay mineral species with a 2:1 expanding crystal lattice.
• Cloisite® Na+ is a highly refined, untreated montmorillonite sold under the trademark of Cloisite® nanoclay by Southern Clay Products.

Some literature can be confusing as the terms Montmorillonite, Smectite and Bentonite are used interchangeably.

Typical physical properties of montmorillonite.

• Chemical Formula: (Na,Ca)_0.33(Al,Mg)₂Si₄O₁₀(OH)₂?nH2O
• Molecular Weight: 540.46
• Density: 2-2.7, average 2.35
• Size: As measured by a transmission electron microscope for a PA6 nanocomposite – 75-150nm X 1nm
• Shape: Platelet
• Charge: 0.50-0.75 in the unit cell
• Surface Area: 750m²/g when exfoliated
• Modulus:  178GPa
• Refractive index: the RI varies with water and iron content
• Alpha: 1.45-1.48
• Gamma: 1.50-1.60
• Delta: 0.02-0.03
• Crystal system: Monoclinic
• Space Group: C2/m
• Bravais Structure:
• a=5.200Å, b=9.200 Å, c=10.130 Å
• α=90.00, β=99.00, γ=90.00
• Mor Hardness: 1-2