# Comparative Analysis of the Solid Conveying of Regrind, Virgin and Powdery Polyolefins in Single-Screw Extrusion

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Used Materials and Characterization of the Geometrical Dimensions and Bulk Density

_{1}, d

_{2}and its height h with 200 measurements for each dimension. The mean value of d

_{1}is 3.55 mm ± 0.14 mm, the mean value of d

_{2}is 4.10 mm ± 0.19 mm and h possesses a mean value of 1.98 mm ± 0.18 mm. The mean projected area of the virgin PP is 12.4 mm

^{2}with a relative standard deviation of 8% (see Figure 4a). Hence, the virgin material shows a very narrow respectively homogeneous granule geometry and size distribution.

^{2}with a large relative standard deviation of 54%, as can be seen in Figure 4b. The large deviations in particle thickness as well as in the projected area make clear that the regrind material exhibits a very inhomogeneous particle shape (see Figure 3) and size (see Figure 4).

#### 2.2. Experimental Set-Up of the Mere Solid Conveying Zone and of the Entire Extruder

^{2}for all three barrels. Employing Equation (4) leads to a free cross-sectional area of the grooves, which is 140.2 mm

^{2}for the helical grooves and 154 mm

^{2}for the axial grooves. In terms of the total free cross-sectional area, which is the sum of ${A}_{\mathrm{s}}$ and ${A}_{\mathrm{g}}$, the helically and the axially grooved barrel purposely show a similar total free cross-sectional area, which only differs by approximately 2%. Thus, differences in throughput between both of the grooved solid conveying zones are primarily caused by a different axial conveying velocity. The values of BZ and BS contained in Equations (7) and (8) are BZ = 0.623 and BS = 0.105 for the helically grooved barrel as well as BZ = 0.578 and BS = 0.105 for the axially grooved barrel.

## 3. Results

#### 3.1. Virgin PP Granule—Results of the Measured, Calculated and Observed Solid Conveying

#### 3.2. Regrind PP Flakes—Results of the Measured, Calculated and Observed Solid Conveying

#### 3.3. Powdery PE Particles—Results of the Measured, Calculated and Observed Solid Conveying

#### 3.4. Results of the Entire Extruder Set-Up Compared to the Mere Solid Conveying Zone

## 4. Conclusions

#### 4.1. Conclusions

#### 4.2. Outlook

## Supplementary Materials

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Schematic representation of three different areas exhibiting varying bulk densities due to different dumping heights in a grooved solid conveying zone. Drawn and kindly provided with the permission to use by E. Grünschloß (author of [10]), March, 2022.

**Figure 2.**Schematic representation of (

**a**) the lenticular virgin PP, (

**b**) the irregularly shaped regrind PP and (

**c**) the powdery PE.

**Figure 4.**Projected area of (

**a**) the virgin PP granule (

**b**) the regrind PP material determined by using a flatbed scanner.

**Figure 5.**Bulk density measurements for increasing dumping height and respective 4-parameter-fits for the virgin PP, the regrind PP and the powdery PE.

**Figure 8.**Virgin PP granule processed with a transparent PMMA barrel exhibiting (

**a**) helical grooves (

**b**) axial grooves.

**Figure 11.**Comparison of the measured throughput for the powdery PE to the calculated throughput (

**a**) for the helically grooved and (

**b**) for the axially grooved barrel.

**Figure 12.**Powdery PE processed with a transparent PMMA barrel exhibiting (

**a**) helical grooves, (

**b**) axial grooves.

**Figure 13.**Comparison of the mass throughput in a whole extrusion set-up at different throttle die pressures to the throughput in a mere helically grooved solid conveying zone (

**a**) for the virgin PP and (

**b**) for the powdery PE.

**Table 1.**Bulk density fit parameter as well as the calculated bulk density values for the three different areas in the grooved solid conveying zone.

Granule | Bulk Density Fit Parameter | Bulk Density | |||||
---|---|---|---|---|---|---|---|

${\mathit{\rho}}_{0}$ in g/cm ^{3} | ${\mathit{h}}_{0}$ in mm | A (Dimensionless) | B (Dimensionless) | ${\mathit{\rho}}_{\mathrm{zz}}$ (2.8 mm) in g/cm^{3} | ${\mathit{\rho}}_{\mathrm{ss}}$ (5.5 mm) in g/cm ^{3} | ${\mathit{\rho}}_{\mathrm{sz}}$ (5.5 mm) in g/cm ^{3} | |

PP-Virgin | 0.519 | 1.698 | 1.095 | 0.518 | 0.303 | 0.420 | 0.462 |

PP-Regrind | 0.218 | 0.230 | 0.042 | 0.914 | 0.069 | 0.113 | 0.144 |

PE-Powder | 0.463 | 1.047 | 2.122 | 0.193 | 0.419 | 0.435 | 0.442 |

**Table 2.**Geometrical dimensions of the utilized screw and of the helically and the axially grooved barrel (data from [28]).

Geometry Parameters | Dimension |
---|---|

Outer screw diameter ${D}_{\mathrm{s}}$ | 34.85 mm |

Core diameter of the screw ${D}_{\mathrm{c}}$ | 23.85 mm |

Helix angle of the screw $\phi $ | 17.73° |

Screw channel depth ${h}_{\mathrm{s}}$ | 5.5 mm |

Width of the screw flight ${w}_{\mathrm{f}}$ | 3.5 mm |

Number of screw flights ${i}_{\mathrm{s}}$ | 1 |

Width of a groove ${w}_{\mathrm{g}}$ | 5.5 mm |

Groove angle $\omega $ | 41.19° (helical) 90° (axial) |

Groove depth ${h}_{\mathrm{g}}$ | 2.8 mm |

Number of grooves ${i}_{\mathrm{g}}$ | 6 (helical) 10 (axial) |

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**MDPI and ACS Style**

Johann, K.S.; Reißing, A.; Bonten, C.
Comparative Analysis of the Solid Conveying of Regrind, Virgin and Powdery Polyolefins in Single-Screw Extrusion. *J. Manuf. Mater. Process.* **2022**, *6*, 56.
https://doi.org/10.3390/jmmp6030056

**AMA Style**

Johann KS, Reißing A, Bonten C.
Comparative Analysis of the Solid Conveying of Regrind, Virgin and Powdery Polyolefins in Single-Screw Extrusion. *Journal of Manufacturing and Materials Processing*. 2022; 6(3):56.
https://doi.org/10.3390/jmmp6030056

**Chicago/Turabian Style**

Johann, Kai S., Adrian Reißing, and Christian Bonten.
2022. "Comparative Analysis of the Solid Conveying of Regrind, Virgin and Powdery Polyolefins in Single-Screw Extrusion" *Journal of Manufacturing and Materials Processing* 6, no. 3: 56.
https://doi.org/10.3390/jmmp6030056