Elastomer toughening of plastics is extensively acknowledged as a robust route to develop high-performance materials. However, the drastic sacrifice of tensile strength resulting from overloading of the elastomer remains unresolved. So far, the elastomers used as toughening agents are mainly non-crosslinked since linear chains are usually considered to exhibit superiority in adsorbing the impact energy. Herein, we found that the microcrosslinking of a commercially available linear elastomer, ethyleneacrylic ester-glycidyl methacrylate terpolymer (EGMA), is significantly beneficial for the toughening of polylactide (PLLA). The reactive micro-crosslinked EGMA (RMCE) with various crosslinking densities was feasibly fabricated through melt processing and used as a more efficient toughener for the brittle PLLA than the linear elastomer. The notched impact strength of the PLLA/RMCE was 35.9 kJ/m 2 , which was more than 5 times that of PLLA/EGMA (7.0 kJ/m 2 ) at the same 15 wt % elastomer loadings. At the same time, the tensile strength and Young's modulus kept high values of 51 MPa and 1.4 GPa, respectively. Synergistic effects such as wide domain size distribution, small ligament thickness, and suitable interfacial adhesion were believed to be main contributors of the increase. The toughening mechanism was further clarified. This work provides a novel avenue to achieve supertoughened PLLA and new insights into the toughening mechanism as well. Such a feasible, versatile, and low-cost method should be widely applicable.
The toughening of poly(L-lactide) (PLLA) with reactive elastic polymers is regarded as an efficient long-standing modification strategy. Extensive investigation indicated the mathematical correlation between the crystallinity of PLLA matrix (X c,PLLA ) and impact toughness by cold crystallization (thermal annealing), but the detailed mechanism has not been clarified. Herein, we present a systematic study on PLLA/reactive elastomer (RECM) blends and demonstrate the significant role of interfacial postreaction during thermal treatment in enhancing toughness. It was confirmed that impact toughness was directly dependent on the time of thermal treatment rather than crystallinity: for the nucleated blend, notched impact strength with identical X c,PLLA increased from 15.0 to 45.3 kJ/m 2 on prolonging the melt crystallization time from 1 to 60 min. The results lead to the conclusion that in situ interfacial postreaction is a critical factor in initiating shear yielding within the entire deformation region and thereby leading to the drastic toughening of PLLA/RECM systems. Furthermore, this work provides deeper insight into the underlying toughening mechanism. The newfound role of interfacial postreaction may offer an industrially scalable relevant model to fabricate high-performance PLLA materials.
Interfacial
compatibilization is acknowledged to be the most effective
approach to improve interfacial strength between the thermodynamically
immiscible components of polymer blends. However, the compatibilizer,
mainly achieved by graft or block copolymers, necessarily connected
by covalent bonds, can rarely be satisfied presently. Herein, we propose
a concept of “quasi-block/graft copolymer” to compatibilize
the immiscible polyolefin elastomer (POE) and poly(styrene-acrylonitrile-glycidyl
methacrylate) (SAG) blends. The quasi-block/graft copolymer was achieved
by the stereocomplex crystals (SC) of poly-l-lactic acid
(PLLA) and poly-d-lactic acid (PDLA) moieties that reactively
grafted on the main chains of the components. By taking advantage
of the interfacial compatibilization through noncovalent forces, the
microphase morphology of the blend can be adjusted and the mechanical
properties can be improved: firstly, the curvature of the phase interface
decreases significantly, facilitating co-continuous morphology on
account of the “rigid” interfacial layers; secondly,
the tensile strength and modulus of the blend are obviously improved;
thirdly, the original phase structure of the blend can be well maintained
during long-term annealing due to the high melting point of the interfacial
SC. This strategy of compatibilizing immiscible blends by using the
hydrogen bonding force of the stereocomplex opens up an idea for interfacial
compatibilization.
Dynamic vulcanisation was employed to prepare blends of isobutylene-isoprene rubber (IIR) and isotactic polypropylene (iPP) with superior properties. The preparation technology, the effects of the presence of IIR on the crystallisation properties of iPP and the mechanical properties of the IIR/iPP thermoplastic vulcanisates (TPVs) were investigated. It was revealed that, under regular shearing at 180uC, dynamic vulcanisation for 10 min produced IIR/iPP TPVs of excellent properties; while degradation occurred when the duration of vulcanisation was extended to 15 min. Incorporation of IIR into iPP dramatically reduced the size of the iPP spherulites, and thus decreased the melting temperature and the degree of crystallinity of the iPP. When the IIR content was 50 wt-%, maximally balanced mechanical properties of IIR/iPP TPVs were obtained with a Charpy impact strength of 53?6 kJ m 22 and a tensile strength of 31?3 MPa.
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