TY - JOUR
T1 - Thermoplastic PLA-LCP Composites
T2 - A Route toward Sustainable, Reprocessable, and Recyclable Reinforced Materials
AU - de Kort, Gijs W.
AU - Bouvrie, Lucienne H. C.
AU - Rastogi, Sanjay
AU - Wilsens, Carolus H. R. M.
N1 - Funding Information:
The research leading to these results has received funding by the H2020 Framework Program of the European Union under grant agreement no. 685614. Vectra LCP 400P grade is a registered trademark of Celanese Corporation, Dallas, TX. The material composition, as well as the results associated with this material are the property of Celanese Corporation. NWO (Nederlandse Organisatie voor Wetenschappelijk Onderzoek) is acknowledged for providing beam time at the ESRF. The staff of the DUBLLE (Dutch Belgian beamline, ESRF) are acknowledged for supporting the X-ray experiments.
Publisher Copyright:
© 2019 American Chemical Society.
PY - 2020/1/13
Y1 - 2020/1/13
N2 - Reprocessing of reinforced composites is generally accompanied by loss of value and performance, as normally the reinforcing phase is damaged, or the matrix is lost in the process. In the search for more sustainable recyclable composite materials, we identify blends based on poly(L-lactide) (PLA) and thermotropic liquid crystalline polymers (LCP) as highly promising self-reinforced thermoplastic composites that can be recycled several times without loss in mechanical properties. For example, irrespective of the thermal history of the blend, injection molded bars of PLA containing 30 wt % LCP exhibit a tensile modulus of 6.4 GPa and tensile strength around 110 MPa, as long as the PLA matrix has a molecular weight of 170 kg mol(-1) or higher. However, after several mechanical reprocessing steps, with the gradual decrease in the molecular weight of the PLA matrix, deterioration of the mechanical performance is observed. The origin of this behavior is found in the increasing LCP to PLA viscosity ratio: at a viscosity ratio below unity, the dispersed LCP droplets are effectively deformed into the desired fibrillar morphology during injection molding. However, deformation of LCP droplets becomes increasingly challenging when the viscosity ratio exceeds unity (i.e., when the PLA matrix viscosity decreases during consecutive reprocessing), eventually resulting in a nodular morphology, a poor molecular orientation of the LCP phase, and deterioration of the mechanical performance. This molecular weight dependency effectively places a limit on the maximum number of mechanical reprocessing steps before chemical upgrading of the PLA phase is required. Therefore, a feasible route to maintain or enhance the mechanical properties of the blend, independent of the number of reprocessing cycles, is proposed.
AB - Reprocessing of reinforced composites is generally accompanied by loss of value and performance, as normally the reinforcing phase is damaged, or the matrix is lost in the process. In the search for more sustainable recyclable composite materials, we identify blends based on poly(L-lactide) (PLA) and thermotropic liquid crystalline polymers (LCP) as highly promising self-reinforced thermoplastic composites that can be recycled several times without loss in mechanical properties. For example, irrespective of the thermal history of the blend, injection molded bars of PLA containing 30 wt % LCP exhibit a tensile modulus of 6.4 GPa and tensile strength around 110 MPa, as long as the PLA matrix has a molecular weight of 170 kg mol(-1) or higher. However, after several mechanical reprocessing steps, with the gradual decrease in the molecular weight of the PLA matrix, deterioration of the mechanical performance is observed. The origin of this behavior is found in the increasing LCP to PLA viscosity ratio: at a viscosity ratio below unity, the dispersed LCP droplets are effectively deformed into the desired fibrillar morphology during injection molding. However, deformation of LCP droplets becomes increasingly challenging when the viscosity ratio exceeds unity (i.e., when the PLA matrix viscosity decreases during consecutive reprocessing), eventually resulting in a nodular morphology, a poor molecular orientation of the LCP phase, and deterioration of the mechanical performance. This molecular weight dependency effectively places a limit on the maximum number of mechanical reprocessing steps before chemical upgrading of the PLA phase is required. Therefore, a feasible route to maintain or enhance the mechanical properties of the blend, independent of the number of reprocessing cycles, is proposed.
KW - mechanical reprocessing
KW - thermotropic polyester
KW - blend
KW - morphology
KW - MECHANICAL-PROPERTIES
KW - FIBER LENGTH
KW - MORPHOLOGY
KW - BLENDS
KW - POLYMER
KW - DEGRADATION
KW - POLYPROPYLENE
KW - RHEOLOGY
U2 - 10.1021/acssuschemeng.9b06305
DO - 10.1021/acssuschemeng.9b06305
M3 - Article
C2 - 32953282
SN - 2168-0485
VL - 8
SP - 624
EP - 631
JO - ACS Sustainable Chemistry & Engineering
JF - ACS Sustainable Chemistry & Engineering
IS - 1
ER -