Reviewed by Lexie CornerNov 5 2024
A team from Eindhoven University of Technology in the Netherlands recently investigated how a novel process can create thermoplastic blends with high interfacial strength using two base materials, utilizing the BESSY II facility. Images captured at the new nano station of the IRIS beamline revealed the formation of nanocrystalline layers during this process, which enhances material performance. The study was published in ACS Applied Materials & Interfaces.
In nano-IR imaging, the layer structures of the pure PVDF/PLLA mixture (left) and the SAD additive (right) are clearly distinguishable. The light and dark colors correspond to the PLLA and PVDF phases, respectively. When SAD is added, the domain sizes of the two phases are reduced. Image Credit: TU Eindhoven/HZB
Bio-based thermoplastics, made from organic, renewable resources, can be recycled after use. Blending these materials with other thermoplastics can enhance their durability; however, the material-to-material contact in these mixtures often needs improvement to achieve optimal properties.
Considered environmentally friendly, bio-based thermoplastics are derived from non-petroleum raw materials and are recyclable like conventional thermoplastics. For example, polylactic acid (PLA), a thermoplastic base material, can be produced from corn or sugar cane.
Researchers worldwide are working to optimize the properties of PLA-based polymers, often by combining them with other thermoplastic base materials. However, this presents significant challenges.
A New Process for Better Blends
A research group from TU Eindhoven, led by Professor Ruth Cardinaels, is currently demonstrating how PLA can be effectively combined with another thermoplastic. They developed a method that allows for the production of certain PLA-based copolymers, such as SAD, during the manufacturing process.
This innovation facilitates the mixing of the two raw materials by creating highly stable (stereo)-crystalline layers at the interfaces between the different polymer phases, utilizing the ICIC approach.
Insights at the IRIS-Beamline
They have identified the processes at BESSY II that ensure the mechanical properties of the mixed thermoplastic are significantly enhanced. To achieve this, they analyzed samples containing PLA-based copolymers at the BESSY II IRIS beamline, as well as pure 50 % blends of the thermoplastics PLA and PVDF.
Stereocomplex Crystals at the Interfaces
Hamid Ahmadi, a Ph.D. student, demonstrated the formation of the PLA-based copolymer SAD using infrared spectroscopy at the IRIS beamline. Additional X-ray observations revealed how SAD formation influences crystallization behavior. The new nano-imaging and spectroscopy capabilities at the IRIS beamline enable advanced chemical visualization and identification of sample areas as small as 30 nm.
This level of precision was essential for determining that stereocomplex crystals are exclusively located at the interface. Infrared nanoscopy images showed a layer of stereocomplex crystals measuring 200–300 nm thick at the interfaces.
Reason for More Stability
The formation of stereocomplex crystals at the interfaces enhances both stability and crystallization temperature. Nucleation at the interface accelerates the overall crystallization process of the PLLA/PVDF blend.
Additionally, the interfacial crystalline layer improves tensile properties by facilitating the transmission of mechanical stresses between the phases, leading to an elongation at break that can increase by as much as 250 %.
By elucidating the location and distribution of the crystalline layer in our samples, we could understand the procedure of mixing much better.
Hamid Ahmadi, Department of Mechanical Engineering, Eindhoven University of Technology
“By developing a new strategy, we have cleared a path for the development of high-performance polymer blends,” Ruth Cardinaels added.
Journal Reference:
Ahmadi, H., et al. (2024) Toughening Immiscible Polymer Blends: The Role of Interface-Crystallization-Induced Compatibilization Explored Through Nanoscale Visualization. ACS Applied Materials & Interfaces. doi.org/10.1021/acsami.4c10829.