Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA)
Abstract
:1. Introduction
- (1)
- In general, temperature most directly affects the crystallization behavior by affecting chain mobility.
- (2)
- The pressure dominates the solubility of the blowing agent and, thereby, the amount of it that is solved in the polymer matrix. Hence, the plasticization effect as well as the gas-induced crystallization is directly influenced by the applied pressure.
- (3)
- During an isothermal saturation phase (time), the crystallization kinetics of PLA is promoted by elevated temperature and the plasticization effect from dissolved blowing agent and is generally governed by the duration.
- (4)
- As a consequence of a sudden pressure drop, which actually induces a thermo-dynamic instability and the prompt oversaturation of the sample the foaming takes place. Hence, the pressure drop rate guides the nucleation rate and the extent of the strain-induced crystallization.
2. Materials and Methods
2.1. Materials
2.2. Methods
2.2.1. Size Exclusion Chromatography (SEC)
2.2.2. Differential Scanning Calorimetry
2.2.3. Rheology
- (1)
- Complex Viscosity: The rheological characterization in shear flow was performed with a plate-plate rheometer Discovery HR-2 hybrid from TA Instruments Waters LLC (New Castle, DE, USA) at 180 °C with a diameter of 25 mm and a gap of 1 mm under nitrogen atmosphere. Dynamic mechanical experiments were carried out in a frequency range from 500 to 0.01 rad/s. The deformation amplitude was set to 5% for all of the measurements. The zero shear viscosity was determined in the frequency region of the Newtonian plateau at a frequency of 0.1 rad/s.
- (2)
- Melt Strength: The Rheotens measurements were carried out to prove the ability of the polymer melt to withstand uniaxial strain. The melt strength was measured while using a Göttfert Rheotens device (Buchen, Germany). The melt strength test samples were prepared using a single screw extruder (L/D ratio of 26) from Göttfert (Buchen, Germany), equipped with a round die of 6 mm in diameter. For each test, a molten polymer strand was drawn down from the die by the two counter-rotating measurement wheels that were mounted on a sensitive force transducer connected to the Rheotens Göttfert 71.97 unit. The tensile force on the polymer melt strand was measured as a function of time or velocity of the measurement wheels. The melt strength is represented by the force at which the strand breaks or in the plateau phase of the rheotens curve. The measurements were carried out at 180 °C and a constant acceleration of 2.4 mm/s2.
2.2.4. Autoclave Foaming
2.2.5. Foam Properties
- (1)
- Scanning Electron Microscopy (SEM): Cryogenic fractured foam samples were investigated by SEM JEOL JSM-6510 (Akishima, Japan). The cell sizes were determined by the use of image analysis software (ImageJ, v1.48, University of Wisconsin, Madison, WI, USA).
- (2)
- Density: The density was determined according to the Archimedes principle with a balance from Mettler Toledo AG245 (Columbus, OH, USA).
3. Results and Discussion
3.1. Basic Properties of the Neat Materials
3.2. Expansion of the Neat Grades
3.3. Foaming Conditions vs. Expansion
4. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Grade & Supposed Usage * (Data Sheet) | Notation | MFR * (g/10 min.) (@ 210 °C, 2.16kg) | D-Content * (%) | GPC Data ** Mw (103 g/mol); Mn (103 g/mol); PDI (-) | ZSV ** T = 180 °C, γ = 5%, 0.1 rad/s (Pas) |
---|---|---|---|---|---|
2003D Packaging | P_4.3D | 6 | 4.3 [4] | 232; 134; 1.73 | 8089 |
3100HP Injection Molding | IM1_2D | 24 | <2 [21] | 162: 107; 1.51 | 1869 |
3251D Injection Molding | IM2_1.4D | 80 | 1.4 [4] | 116; 78; 1.49 | 243 |
3260HP Injection Molding | IM3_2D | 65 | <2 [21] | 111; 75, 5; 1.47 | 483 |
4032D Film | Fi_2D | − | 1.4–2.0 [4] | 232; 149; 1.55 | 5716 |
4044D Extrusion | X_4D | − | ~4 [21] | 230; 117; 1.97 | 7794 |
4060D Hot Sealing | HS_12D | − | 12–12.3 [4] | 217; 118; 1.84 | 4200 |
7001D Injection Stretch Blow Molding | BM_4.4D | 6 | 4.4 ± 0.5 [4] | 242; 142; 1.71 | 8472 |
8052D Foaming | Fo_4.7D | 14 | 4.7 [4] | 178; 109; 1.64 | 3457 |
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Standau, T.; Long, H.; Murillo Castellón, S.; Brütting, C.; Bonten, C.; Altstädt, V. Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA). Materials 2020, 13, 1371. https://doi.org/10.3390/ma13061371
Standau T, Long H, Murillo Castellón S, Brütting C, Bonten C, Altstädt V. Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA). Materials. 2020; 13(6):1371. https://doi.org/10.3390/ma13061371
Chicago/Turabian StyleStandau, Tobias, Huan Long, Svenja Murillo Castellón, Christian Brütting, Christian Bonten, and Volker Altstädt. 2020. "Evaluation of the Zero Shear Viscosity, the D-Content and Processing Conditions as Foam Relevant Parameters for Autoclave Foaming of Standard Polylactide (PLA)" Materials 13, no. 6: 1371. https://doi.org/10.3390/ma13061371