CPVC vs PVC Dry Blending

[Len]

Dear Members and Friends,

I know there are few CPVC formulators and compounders out there, and most of what they know is proprietary information. I can’t ask for details regarding formulation or proprietary processing, but I could sure use some helpful advice.

I'm looking for insight into the differences and similarity between dry blending techniques for PVC resin and CPVC resin. General consideration for dry blending that set CPVC apart from or mimic rigid PVC dry blending.

Too Much Resin - For example, is batch weight/load the same for both resins, given a constant mixer volume? I've been using about 1600 to 2000 g as my initial PVC resin weight (rigid compound) in my lab mixer. When I mix CPVC at that same resin weigh, 1600 g, (on the low end of my batch weight), the mixer seems to bog down and struggle to maintain rpm during the mix cycle. Do I need to start w/ a smaller batch weight?

Sequence of Addition - I us a standard mixing sequence for rigid PVC, would I need to make changes for a CPVC batch? Sequence/Temps:

Resin.... Start, Ambient
Stabilizer.... 80 F
Lubs.... 125 F
PA/IM, Acrylic.... 175 F
Pigment/filler.... 180 F
Drop.... 200 - 205 F

When dry blend processing CPVC, at about 125 - 175 F I start to lose mixer speed and frictional heat. The 1600 g resin load appears to be sticky, not a free-flowing powder. Other than specific details about time and drop temperature, is this sequence good for CPVC? Or should I be aware of some changes; like adding the IM separate for the PA, or dropping the lubs earlier/later?

Please help me to understand this beast, so I can make a better CPVC dry blend. Hints and advice much appreciated.

Thanks,

Len

[Skip]

Len---I've not had much experience blending CPVC, and very little extrusion experience--except to know that it's a high amp, high torque melt during extrusion---and I used a good slug of AC629A PE wax to get decent rates.
As to blending, I don't know particle morphology--whether it's an aborbing popcorn particle or not. Also, how does bulk density compare to PVC---grams/liter? If much higher, that could translate to higher mixer torques.

Two folks who would know alot about this are Jim Summers and Ella Rabinowtz (ex Geon) who formed P3 Consulting.
I think they have a web site.
Sorry I couldn't be more help.

[Len]

Thank you for the help, Skip!

I'll follow up on the leads, too.

Len

[NickTucker]

Len, I have done some work in the past and here are some observations which may help a) the bulk density is much higher for CPVC compounds(0.65g/cc) and the batch weight would be definitely more with CPVC b) the overloading you are seeing is because of the dry blend fusing in the mixer . you need to optimise on the processing aid and lubricants c) the drop temperature is a bit higher for CPVC , but iam not sure about the exact temperature.

iam not sure whether this helped...let me know if you need anything more.
Nick

[Len]

Nick,

Thanks for the tips!

Just for added clarification, the formulation has a huge shot of CPE. I don't quite understand why it has 25 phr of CPE in it, but there it is! I added the CPE w/ the CPVC on my first attempt, dry blending. This batch seemed to get lumpy and wet looking after the lubs and PA were added, temp at about 175. The mixer would not continue heating the blend at that point. Like a plasticized compound, awaiting dry up; lose of amps and slow or no heating. Puzzling. I've made some progress since these early mixer trials, but still need some help.

There is no other impact Modifier in the formulation, PA's are typical of rigid PVC K-125/K-175, w/ a bit more K-175 than the usual PVC compound. Lubs are AC629A and Wax 250.

I thought a little more detail would help guide your advice.

Len

[NickTucker]

Hi Len, the CPE loading is toooooooo high. CPE does have a fluidising/plasticating effect(not too sure whether this is way to express it) and this is possibly what you are seeing in the mixer. Total impact modifier loading should not exceed 7-8phr(Iam assuming this is a plumbing pipe formulation). Try a MBS type. It works better. Yes a combination of K120/K175 (with higher K175) should work. And yes a combination of an oxidised PE wax and Paraffin/non-polar/FT wax would work well.
Just curious...If you can share...what are you working on??
Nick