The effects of rare earth based β-nucleating agent (WBG-II) and aryl amide derivative nucleating agent (TMB-5000) on the crystal structure, morphology, and dynamic mechanical behavior of poly(L-lactic acid) (PLLA) were systematically investigated. The presence of β-form crystal in PLLA composites has been confirmed through various techniques including wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The crystallization behaviors of WBG-II and TMB-5000 nucleated PLLA were studied via WAXD and polarized optical microscope (POM) techniques. The experimental results convincingly reveal that WBG-II and TMB-5000 not only accelerate the crystallization rate, but also alter the packing structure of PLLA chains in the crystals. Furthermore, a significant difference in crystal dimensions and nucleation density was observed clearly. Moreover, the effect of different β-nucleating agents on the storage modulus (E′) and dynamic loss (tan δ) of pure PLLA, PLLA/TMB-5000_0.25 and PLLA/WBG-II_0.25 were investigated by dynamic mechanical analysis (DMA).

In this study, a series of poly(l-lactide) and (3-amino)-propylheptaisobutyl cage silsesquioxane (PLLA-AMPOSS) intermediates were first fabricated using single-arm in situ solution polymerization of LLA monomers and AMPOSS nanoparticles with different contents, 0.02–1.00 mol%. Then, the PLLA-AMPOSS intermediate with 0.5 mol% AMPOSS was selected as a representative and investigated by nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). Afterwards, it was added into the pure PLLA with different mass fractions. Finally, the thermal behavior, crystallization kinetics, morphological characteristics, and mechanical properties of the obtained PLLA/PLLA-AMPOSS nanocomposites were carefully measured and investigated by differential scanning calorimetry (DSC), polarizing microscopy (POM), scanning electron microscopy (SEM), and tensile test. After comparing the PLLA-AMPOSS intermediate and PLLA/AMPOSS blend, the results show that the ring-open polymerization of PLLA-AMPOSS intermediate was successful. The results also show that the existence of PLLA-AMPOSS has a strong influence on the crystallization behavior of PLLA/PLLA-AMPOSS composites, which can be attributed to the heterogeneous nucleation effect of PLLA-AMPOSS. In addition, it was also found from the tensile test results that the addition of the PLLA-AMPOSS nanofiller improved the tensile strength and strain at break of PLLA/PLLA-AMPOSS nanocomposites. All of these results indicate the good nucleating effect of PLLA-AMPOSS and that the AMPOSS disperses well in the PLLA/PLLA-AMPOSS nanocomposites. A conclusion can be drawn that the selective nucleating agent and the combined method of in situ ring-opening polymerization and physical blending are feasible and effective.

The friction stir welding (FSW) of thermoplastic polymers is gradually receiving attention because of its advantages including high efficiency and pollution-free manufacturing. The extrusion-based additive manufacturing (EAM) of polymers has also become one of the main processing methods for thermoplastic parts. In this paper, a hybrid manufacturing method for the FSW process and EAM technology is proposed and explored. The effects of the FSW process using two different welding tools on the mechanical behaviors of 3D printing polymer parts were compared and investigated and the corresponding mechanism was analyzed. The results show that the appropriate welding tool is beneficial for eliminating the anisotropy and decreasing the porosity of 3D-printed parts. Therefore, the improving effects of the FSW process on the mechanical behaviors of the EAM parts are verified. The mechanism was attributed to the high-speed rotation of the welding tool with the appropriate shape, which can promote the flow of polymer melt in the welding region, leading to the formation of dense structures caused by the entanglement of the molecular chains. This study may provide some assistance in modern industrial manufacturing for the processing of large custom components.

Graphical abstract Polyglycolide-based polyurethane was synthesized via chain extension reaction. As the hard segment content increases, its thermal stability and mechanical properties are improved; and the weight loss rate in PBS solution is reduced. Abstract Novel degradable polyglycolide-based polyurethanes (PGAUs) were synthesized using polyglycolic diol (PGA diol) as soft segment, 1,6-n-hexane diisocyanate (HDI) as hard segment, and 1,4-butanediol (BDO) as chain extender agent. PGA diol (M _n = 10,000 g·mol⁻¹) was obtained by ring-opening polymerization of glycolide in the presence of BDO using stannous octanoate (Sn(Oct)₂) as a catalyst. The structures of PGA diol and PGAUs were characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR). The PGA diol and PGAUs were further studied by the means of differential scanning calorimetry, thermogravimetric analysis, tensile testing, scanning electron microscope, and hydrolytic degradation behavior testing. FTIR and ¹H NMR analyses indicated that the PGAUs were easily prepared by chain-extension reaction. The results showed that the PGAUs had improved thermal stability and enhanced mechanical properties with the hard segment increased. Degradation behavior suggested that the PGAUs could be degraded in phosphate-buffered saline solution.