Biobased PLA/NR-PMMA TPV with balanced stiffness-toughness: In-situ interfacial compatibilization,performance and toughening model

Using rubber to toughen polylactide (PLA) is always accompanied by the sharp reduction in stiffness. Herein, PLA/poly (methyl methacrylate) grafted natural rubber (NR-PMMA) thermoplastic vulcanizates (TPVs) with balanced stiffness-toughness were fabricated. With the addition of 40 wt % NR-PMMA, the impact strength and tensile toughness of PLA/NR-PMMA TPV significantly improved to about 102.7 kJ/m² and 66.1 MJ/m³, respectively, compared with those of 2.7 kJ/m² and 2.4 MJ/m³ for the pure PLA. Meanwhile, the yielding stress was maintained at 34.5 MPa. Fourier transform infrared spectroscopy (FTIR) confirmed the formation of in-situ interfacial compatibilization between PLA and rubber phases. Both tensile and impact toughening mechanism were studied and deduced as considerable energy dissipation provided by the continuous rubber phase. Instrumented notched impact tests demonstrated that the energy dissipating in crack propagation process contributed to the main part of impact toughness. In addition, a novel toughening model based on bicontinuous structure was incorporated, which showed good applicability in predicting the impact strength of PLA/NR-PMMA TPVs.     

Enhancing toughness of poly (lactic acid)/Thermoplastic polyurethane blends via increasing interface compatibility by polyurethane elastomer prepolymer and its toughening mechanism

Due to the environmental pollution caused by the petroleum-based polymer, poly (lactic acid) (PLA), a biodegradable and biocompatible polymer that obtained from natural and renewable sources, has attracted widespread attention. However, the brittleness of PLA greatly limits its application. In this study, the super toughened PLA-based blends were obtained by compatibilizing the PLA/thermoplastic polyurethane (TPU) blends with the polyurethane elastomer prepolymer (PUEP) as an active compatibilizer. The mechanical properties, thermal properties and corresponding toughening mechanism of PLA/TPU/PUEP system were studied by tensile test, instrumented impact test, dynamic mechanical analysis (DMA), scanning electronic microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). All the results demonstrate that the isocyanate (−NCO) group in PUEP is successfully reacted with the –OH groups at both sides of the PLA and the obtained polyurethane (PU)~PLA copolymer (PU ~ cõ PLA) significantly improves the interfacial compatibility of PLA/TPU blends. The gradually refined dispersed phase size and fuzzy phase interface as displayed in SEM images suggest a good interfacial compatibilization in the PLA/TPU/PUEP blends, probably due to the isocyanate reaction between PLA and PUEP. And the interfacial reaction and compatibilization among the components led to the formation of super toughened PLA/TPU/PUEP blends. And the instrumented impact results indicate that most of the impact toughness is provided by the crack propagation rather than the crack initiation during the entire fracture process.     

Comparison of low-velocity impact damage in thermoplastic and thermoset composites by non-destructive three-dimensional X-ray microscope

This paper presents a method for the non-destructive inspection and quantitative comparison of low-velocity impact damage in thermoplastic and thermoset composites. X-ray microscope (XRM) computed tomography is used to analyse the three-dimensional internal damage in carbon fibre/poly-ether-ether-ketone (AS4/PEEK) and carbon fibre/epoxy (CCF300/Epoxy) laminates. With the materials and testing conditions used, it was shown that thermoplastic composites have better interlaminar and intralaminar properties, and the following quantitative conclusions were drawn. Under the same impact energy, the maximum contact force of AS4/PEEK laminate was approximately twice that of CCF300/Epoxy laminate. Dissection of the reconstructed XRM volume along a characteristic slicing surface showed that AS4/PEEK had less internal damage than CCF300/epoxy. When the impact energy was 15 J, the XRM results showed that the sum of delamination areas between each ply in AS4/PEEK was only 9% of that in CCF300/Epoxy, whereas the ultrasonic C-scan results showed that the total delamination area of AS4/PEEK was 54.78% of that of CCF300/Epoxy.     

Direct diazotization of graphite nanoplatelets with melamine and their favorable application in epoxy resins

The ease of undesirable agglomeration and a low efficiency are two problems that restrict the application of graphite nanoplatelets (GNPs) in epoxy resins (EP). Herein, a new strategy with melamine (MEL) as the precursor to functionalize GNPs chemically, which form a bonding layer that is compatible with epoxy matrix, is reported. The MEL fragments with secondary amine groups were grafted uniformly on the GNPs surface by covalent junctions to exploit the diazonium chemistry. This behavior led to a better dispersion and a stronger interaction with the epoxy matrix and resulted in an enhanced glass transition temperature and bending strength, compared with the pure EP. When only 1 wt% functionalized GNPs (f‐GNPs) was used, the Tg of the modified EP raised of about 15°C compared with pure EP, and the bending strength increased by approximately 39%. The dielectric constant of the EP with f‐GNPs was impacted slightly, and the dielectric loss decreased. At 10⁵ Hz, the dielectric loss of the EP with 1 wt% f‐GNPs decreased by approximately 11% compared with pure EP. Therefore, diazotization modification of the GNPs is a useful approach to improve the compatibility in nanoparticle networks.     

L‐lysine and EDTA polymer mimics as resins for the quantitative and reversible removal of heavy metal ion water pollutants

Traditional precipitation methods for inorganic micropollutant removal from waters are increasingly being replaced by sorption methods based on both natural and synthetic materials. In this context, two novel effective heavy metal ions absorbers are presented. These resins, LYMA and LMT85, were crosslinked poly(amidoamine)s carrying amine and carboxyl groups in their repeating units. In particular, the LYMA‐repeating unit contains one carboxyl and two amine groups and is a mimic of L ‐lysine, whereas LMT85 contains two amine and five carboxyl groups and is a mimic of EDTA. Both resins were prepared at moderate cost by simple eco‐friendly procedures. The heavy metal ion set adopted as benchmark was Cu²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Ni²⁺, and Co²⁺. LYMA proved selective for Cu²⁺ and Ni²⁺, the other ions tested being negligibly absorbed, whereas LMT85 proved capable of rapidly and quantitatively absorbing all the ions tested either singly or in mixed solution. The absorption process was reversible, and the resins were easily regenerated by acidification. The absorption of several metal ions imparted intense coloring to the resins, a feature possibly exploitable for analytical purposes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The dispersion of pigment slurries via incorporation with water-soluble sulfonate poly(ethylene terephthalate)

A water-soluble sulfonate poly(ethylene terephthalate) copolymer has been synthesized and identified as a high-temperature endurable surfactant. The glass-transition temperature and the storage modulus increase in correlation to the increase in sulfonate content. Various characterization studies were performed, including light scattering, zeta-potential measurement and a sedimentation test. The results suggest that at equal numbers of sulfonate units in a solution, a low concentration of a dispersant of high sulfonate content is more effective than a high concentration of a dispersant of low sulfonate content. Received: 6 April 2000 Accepted: 23 September 2000     

A new strategy for solid phase synthesis of a secondary amide library using sulfonamide linker via radical traceless cleavage

A new strategy for solid phase synthesis of a secondary amide library using sulfonamide linker via radical traceless cleavage is reported. Polystyrylsulfonyl chloride (1) reacted with primary amines to afford polystyryl-supported N-alkyl sulfonamides (2), which were acylated with acid chlorides and followed by radical cleavage with TiCl₄/Zn to afford secondary amides. It was interestingly found that the products released from acyl alkanesulfonamide resins are closely dependent on the substituents of benzene rings of alkyl or acyl groups on the resins. When the substituent on benzene ring of N-benzyl group of sulfonamides is an electron rich MeO-group, the products released from sulfonamide resins are dependent on the substitution position on benzene ring: para-MeO- to yield 1,2-bis (p-methoxylphenyl)ethane and N-p-methoxylbenzyl benzamide (30:1); ortho-MeO- to give 1,2-bis (o-methoxylphenyl)ethane and N-o-methoxylbenzyl benzamide (1:15); and meta-MeO- only to release N-m-methoxylbenzyl benzamide. Neither N-benzoyl sulfonamide resins on benzene ring with electron-drawing para-O₂N-, nor the one with electron-donating para-H₂N- could release any amide product, while the N-benzoyl sulfonamide resins on benzene ring with para-acetamido group released para-acetamidobenzamides. The conjugation effect to stabilize the radical groups in the radical cleaving process was observed.     

Multigraft copolymer superelastomers: Synthesis morphology, and properties

The synthesis of well-defined multigraft copolymers having a polydiene backbone with polystyrene side chains is briefly reviewed, with particular focus on controlling branch point spacing and branch point functionality. Use of living anionic polymerization and chlorosilane linking chemistry has led to the synthesis of series of materials having regularly spaced trifunctional (comb), tetrafunctional (centipede), and hexafunctional (barbwire) branch points. The morphologies of these materials were characterized by transmission electron microscopy and small-angle X-ray scattering, and it was found that the morphologies were controlled by the local architectural asymmetry associated with each branch point. Mechanical properties studies revealed that such multigraft copolymers represent a new class of thermoplastic elastomers (TPEs) with superior elongation at break and low residual strains as compared to conventional TPEs.