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.