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Fused deposition modeling (FDM) is currently the most popular 3D printing method, where thermoplastic polymers are predominantly used. Among them, the biobased poly(lactic acid) (PLA) governs the FDM filament market, with demand higher than supply, since not all grades of PLA are suitable for FDM filament production. In this work, the effect of a food grade chain extender (Joncryl ADR® 4400) on the physicochemical properties and printability of PLA marketed for injection molding was examined. All samples were characterized in terms of their mechanical and thermal properties. The microstructure of the filaments and 3D-printed fractured surfaces following tensile testing were examined with optical and scanning electron microscopy, respectively. Molecular weight and complex viscosity increased, while the melt flow index decreased after the incorporation of Joncryl, which resulted in filaments of improved quality and 3D-printed constructs with enhanced mechanical properties. Dielectric spectroscopy revealed that the bulk properties of PLA with respect to molecular mobility, both local and segmental, were, interestingly, not affected by the modifier. Indirectly, this may suggest that the major effects of the extender are on chain length, without inducing chain branching, at least not to a significant extent.

Melts of multiarm stars of 1,4-polybutadiene (dendrimer arborescent hybrids) with very high branching functionality ($f$) and small arm molar mass behave as jammed colloids and show distinct layers of segmental mobility. Three mobility layers were identified, comprising outer, intermediate, and near-core segments, all displaying a Vogel-Fulcher-Tammann temperature dependence. The respective glass temperatures increase as ${f}^{1/2}$. Our findings pave the way for further progress in this field by reconsidering previous theoretical treatments based on a single friction coefficient in hybrid nanoparticles such as densely grafted stars.

Two different classes of hairy self-suspended nanoparticles in the melt state, polymer-grafted nanoparticles (GNPs) and star polymers, are shown to display universal dynamic behavior across a broad range of parameter space. Linear viscoelastic measurements on well-characterized silica-poly(methyl acrylate) GNPs at fixed core radius (R(core)) and grafting density (or number of arms f), but varying arm degree of polymerization (N(arm)) show two distinctly different regimes of response. A colloidal Regime I at small N(arm) (large core volume fraction), with a predominant low-frequency solid-like colloidal plateau and ultraslow relaxation, and a polymeric Regime II at large N(arm) (small core volume fractions), with a response dominated by the star-like relaxation of partially interpenetrated arms. The transition between the two regimes is marked by a cross-over where both polymeric and colloidal modes are discerned albeit without a distinct colloidal plateau. Similarly, polybutadiene multiarm stars also exhibit the colloidal response of Regime I at very large f and small N(arm). The star arm relaxation model and a simple scaling model of nanoparticle escape from the cage of neighbors by overcoming a hopping potential barrier due to their elastic deformation, describe quantitatively the linear response of the polymeric and colloidal regimes, respectively, in all these cases. The dynamic behavior of hairy nanoparticles of different chemistry and molecular characteristics, investigated here and reported in the literature, can be mapped onto a universal dynamic diagram of [Formula: see text] as a function of [Formula: see text] , where [Formula: see text] is the monomeric volume. In this diagram, the two regimes are separated by a line where the hopping potential ΔU(hop) is equal to the thermal energy, k(B)T. ΔU(hop) can be expressed as a function of the overcrowding parameter x, i.e. the ratio of f to the maximum number of unperturbed chains with N(arm) that can fill the volume occupied by the polymeric corona, hence this crossing is shown to occur when x=1. For x>1 we have colloidal Regime I with overcrowded volume, stretched arms and ΔU(hop) > k(B)T, while polymeric Regime II is linked to x