Improving recyclebot concepts

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For main page see: recyclebot and latest version RepRapable Recyclebot: Open source 3-D printable extruder for converting plastic to 3-D printing filament

These ideas were generated from the study: Shan Zhong, Pratiksha Rakhe and Joshua M. Pearce. Energy Payback Time of a Solar Photovoltaic Powered Waste Plastic Recyclebot System. Recycling 2017, 2(2), 10; doi: 10.3390/recycling2020010 open access

Heating Section

  • Three heating sections with varied temperature are helpful, which can be obtained by changing the coil density.
  • Heating section-2 is in the middle of the heating tube. The temperature on the section-2 should be at a point where the plastic can be totally melted.
  • Heating section-1 is on the feeding side and heating section-3 is on the extrusion side. The temperatures on section-1 and section-3 should be slightly lower than that on section-2 [1]. Heating section-1 is for pre-heating the plastic. Plastic after heating section-3 should have enough viscosity to form filament, and the viscosity is varied with temperature for the same plastic.
  • The temperature on the nozzle should be close to the temperature on heating section-3. It is important to keep the nozzle with a stable temperature because the nozzle easily loses heat.

Driving Section

  • 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 tubes and rather high auger speeds, which can decrease the residential time and enable the plastic to 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 Section

  • Uniform feeding rate is important for keeping stable temperature and pressure in the heating tube.
  • Fluctuating temperature would lead to degradation of the plastic and unstable pressure in the heating tube would result in the variation of the filament diameter which is bad for accurate 3-D printing.

Chain Extender

  • To recycle the plastic which is easy to degrade, using a chain extender can increase the viscosity of plastic and make it easy to form filament. However, the amount of the chain extender used 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 [6] [7] [8] [9].


  1. Pettit, G. Plastic extruder temperature control system. U.S. Patent 3,733,059, issued May 15, 1973.
  2. 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.
  3. 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.
  4. 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.
  5. Oromiehie, Abdulrasoul, and Alireza Mamizadeh. Recycling PET beverage bottles and improving properties. Polymer international 2004;53(6):728-732.
  6. Torres, N., J. J. Robin, and B. Boutevin. Chemical modification of virgin and recycled poly (ethylene terephthalate) by adding of chain extenders during processing. Journal of Applied Polymer Science 2001;79(10): 1816-1824.
  7. Akkapeddi, M. K., and J. Gervasi. Chain extension of PET and nylon in an extruder. In ACS Division of Polymer Chemistry Meeting 1988:567-570.
  8. Inata, Hiroo, and Shunichi Matsumura. Chain extenders for polyesters. I. Addition‐type chain extenders reactive with carboxyl end groups of polyesters. Journal of applied polymer science 1985;30(8):3325-3337.
  9. Inata, Hiroo, and Shunichi Matsumura. Chain extenders for polyesters. III. Addition‐type nitrogen‐containing chain extenders reactive with hydroxyl end groups of polyesters. Journal of applied polymer science 1986:32(4):4581-4594.