Heating Session
- Three heating sessions with varied temperature is helpful. Three heating sessions can be obtained by changing the coil density.
- Heating session-2 is in the middle of the heating tube. The temperature on the session-2 should be at a point where the plastic can be totally melted in the session-2.
- Heating session-1 is on the feeding side and heating session-3 is on the extrusion side. The temperatures on session-1 and session-3 should be slightly lower than that on session-2 [1]. Heating session-1 is for pre-heating the plastic. Plastic after heating session-3 should have enough viscosity to form filament, and the viscosity is varied with temperature for the same plastic.
- The temperature on nozzle should be close to the temperature on heating session-3. It is important to keep the nozzle with a stable temperature because nozzle is easy to lose heat.
Driving Session
- The two main purposes for driving system are to deliver plastic and compress plastic.
- To reduce the degradation of the plastic during recycling, it is necessary to decrease the residential time for plastic in the heating tube. It is better to use long heating tube and rather high auger speed, which can decrease the residential time and make the plastic be heated more consistently. The normal screw rotation speed is 45-210 rpm [2] [3] [4] [5].
- If the size of the auger on the nozzle end is slight bigger than other parts, it’s better for the auger to compress the plastic in the tube.
Feeding Session
- Uniform feeding rate is important for keeping stable temperature and pressure in the heating tube.
- Fluctuated temperature would lead to degradation of the plastic and unstable pressure in the heating tube would result in the variation of the filament size.
Chain Extender
- To recycle the plastic which is easy to degrade, using the chain extender can increase the viscosity of plastic and make it easy to form filament. However, the usage amount of the chain extender is usually tiny, so it is difficult but important to make uniform distribution of chain extender in the plastic pellets.
- Some examples of chain extenders for PET cited in the literature are diepoxides, diisocyanates, dianhydrides, bis-oxazolines, carbodiimides, bis-dihydrooxazines.
Reference
- ↑ Pettit, G. Plastic extruder temperature control system. U.S. Patent 3,733,059, issued May 15, 1973.
- ↑ Cook, Wayne D., Graeme Moad, Bronwyn Fox, Gary Van Deipen, Tie Zhang, Ferenc Cser, and Lawry McCarthy. Morphology–property relationships in ABS/PET blends. II. Influence of processing conditions on structure and properties. Journal of applied polymer science 1996;62(10):1709-1714.
- ↑ Chengcheng, Wan, Wang Yilong, and Shen Rui. The Changes of Intrinsic Viscosity of PET Bottle Flakes after Reactive Extrusion. Modern Plastics Processing and Applications 2015;2:007.
- ↑ Awaja, Firas, Fugen Daver, and Edward Kosior. Recycled poly (ethylene terephthalate) chain extension by a reactive extrusion process. Polymer Engineering & Science 2004;44(8):1579-1587.
- ↑ Oromiehie, Abdulrasoul, and Alireza Mamizadeh. Recycling PET beverage bottles and improving properties. Polymer international 2004;53(6):728-732.