if we got shielding properties of composite 50%filler and 50%wax and achieved 23 dB shielding properties it is good or not? the filler is conductive polymer with low loading of CNT.
Have you done a literature search so you can compare your results with other CNT-containing polymeric materials (for example, on a quick google search, things like this: Article Electromagnetic Interference Shielding Mechanisms of CNT/Pol...
)
Or articles such as this for 100% CNT films (Article Electromagnetic interference shielding of carbon nanotube macrofilms
)
These and the references within them should give you a baseline to work from.
You asked if it is good or not a shielding effectiveness of 23 dB? That’s depend of your target!
You obtained now a field attenuation of about 14 times (corresponding to 23 dB). That’s could be or not enough for your interest. But the shielding effectiveness always depends of the frequency (I suppose that you have measured on a sample and not of a real shield, because in this last case must be taken in consideration, additionally, other parameters). If in the interesting frequency range the attenuation is about 120 dB it is almost perfect. But practically, it is very difficult to obtain such attenuation, and also it is very difficult to measure it.
Very roughly: you can routinely achieve shielding effectiveness of about 20-30 dB wih carbon based fillers (carbon black, graphite, carbon nanotube and their combinations) but that is not too much. 30-40-50 dB can be achiwved with metal-coated glass or carbon fibers or with stainless steel fibers which is almost aceptable. 60-70 dB can be achieved with high quality electroless plating on plastics, which is excellent.