In this study, the performance of three aliphatic oxalamide based compounds as nucleating agent (NA) for isotactic polypropylene (iPP) has been evaluated. The NAs evaluated in this study contain two oxalamide motifs that are connected through linking spacers with 2, 3, or 4 methylene units in between the oxalamide groups, while containing flexible hexyl end-groups on the outside. It is demonstrated that the onset of crystallization in the presence of these NAs under quiescent conditions, generally observed around 120−125 °C, is strongly dependent on both the crystallization conditions and NA concentration. Although these oxalamide compounds are only moderately effective under quiescent conditions, they show promise for use under industrially relevant processing conditions that require high cooling and shear rates: When the NA is forced to undergo shear-induced self-assembly and shearalignment during cooling, the onset of crystallization of the iPP phase is observed in SAXS at temperatures up to 140 °C.

We report on the effect of an aliphatic oxalamide based nucleating agent (OXA3,6) on the melt and crystallization behavior of isotactic polypropylene (iPP) under defined shear conditions. Through polarized optical microscopy, we demonstrate that OXA3,6 self-assembles from the iPP melt into rhombic crystals whereas their size and distribution proved highly dependent on the employed cooling rates. The presence of 0.5 wt % of OXA3,6 in iPP results in a significant suppression in iPP melt viscosity, which could not be explained via molecular modeling. A possible cause for the drop in viscosity in the presence of OXA3,6 is attributed to the interaction (absorption) of high molecular weight iPP chains with the nucleating agent, thereby suppressing their contribution to the viscoelastic response of the melt. This proposed mechanism for the suppression in melt viscosity appears similar to that encountered by the homogeneous distribution of nanoparticles such as CNTs, graphene, and silica. Shear experiments, performed using a slit flow device combined with small-angle X-ray diffraction measurements, indicate that crystallization is significantly enhanced in the presence of OXA3,6 at relatively low shear rates despite its lowered sensitivity to shear. This enhancement in crystallization is attributed to the shear alignment of the rhombic OXA3,6 crystals that provide surface for iPP kebab growth upon cooling. Overall, the suppression in melt viscosity in combination with enhanced nucleation efficiency at low as well as high shear rates makes this self-assembling oxalamide based nucleating agent a promising candidate for fast processing.

We report on the role of temperature and shear on the melt behavior of iPP in the presence of the organic compound N1,N1′-(propane-1,3-diyl)bis(N2-hexyloxalamide) (OXA3,6). It is demonstrated that OXA3,6 facilitates a viscosity suppression when it resides in the molten state. The viscosity suppression is attributed to the interaction of iPP chains/subchains with molten OXA3,6 nanoclusters. The exact molecular mechanism has not been identified; nevertheless, a tentative explanation is proposed. The observed viscosity suppression appears similar to that encountered in polymer melts filled with solid nanoparticles, with the difference that the OXA3,6 compound reported in this study facilitates the viscosity suppression in the molten state. Upon cooling, as crystal growth of OXA3,6 progresses, the decrease in viscosity is suppressed. Retrospectively, segmental absorption of iPP chains on the surface of micrometer-sized OXA3,6 crystallites favors the formation of dangling arms, yielding OXA3,6 crystallites decorated with partially absorbed iPP chains. In other words, the resulting OXA3,6 particle morphology resembles that of a hairy particle or a starlike polymer chain. Such hairy particles effectively facilitate a viscosity enhancement, similar to branched polymer chains. This hypothesis and its implications for the shear behavior of iPP are discussed and supported using plate–plate rheometry and slit-flow experiments combined with small-angle X-ray scattering analysis.

In this study, we report on the visco-elastic response during start-up and cessation of shear of a novel bio-based liquid crystal polymer. The ensuing morphological changes are analyzed at different length scales by in-situ polarized optical microscopy and wide-angle X-ray diffraction. Upon inception of shear, the polydomain texture is initially stretched, at larger strain break up processes become increasingly important, and eventually a steady state texture is obtained. The shear stress response showed good coherence between optical and rheo-X-ray data. The evolution of the orientation parameter coincides with the evolution of the texture: the order parameter increases as the texture stretches, drops slightly in the break up regime, and reaches a constant value in the plateau regime. The relaxation of the shear stress and the polydomain texture showed two distinct processes with different timescales: The first is fast contraction of the stretched domain texture; the second is the slow coalescence of the polydomain texture. The timescale of the orientation parameter’s relaxation matched with that of the slow coalescence process. All processes were found to scale with shear rate in the tested regime. These observations can have far reaching implications for the processing of liquid crystal polymers as they indicate that increased shear rates during processing can correspond to an increased relaxation rate of the orientation parameter and, therefore, a decrease in anisotropy and material properties after cooling.

In this work, we report on a novel hydrogenb o n d i n g c o m p o u n d , N , N ′ -b i s ( 2 -h y d r ox y e t h y l )terephthalamide (BHET), and its potential as additive in poly-L-lactide (PLA). Although the hydroxyl groups of BHET can participate in transesterification with the PLA matrix, we demonstrate through gel permeation chromatography that extrusion at 200 °C does not result in a drastic decrease in molecular weight. When dissolved in the PLA matrix, BHET facilitates a plasticizing effect, indicated by a suppression in both melt viscosity and glass-transition temperature. Additionally, BHET can crystallize from the PLA melt during cooling, where the generated BHET crystals facilitate heterogeneous nucleation of the PLA matrix. In general, BHET crystallization is favored at high undercooling/superstaturation, as this yields BHET crystals with a high surface area-to-volume ratio. However, rapid cooling to temperatures below the glass-transition temperature prevents the crystallization of the BHET, effectively yielding samples where only the plasticizing effect of BHET is evident. A suppression in yield point is observed during mechanical analysis of samples with increasing BHET concentration, a characteristic feature for samples with decreasing glass-transition temperatures. In contrast, when allowed to crystallize during processing, BHET can be used to generate PLA crystals oriented along the flow direction, effectively enhancing the tensile modulus. Overall, the combined plasticizing and nucleating effect of BHET makes it a verstaile additive for controlled processing and performance of PLA.

In this study, we report on the synthesis and characterization of thermosets based on the renewable N,N′-octamethylene-bis­(pyrrolidone-4-carboxylic acid) (BP-C8) and 1,3-bis­(4,5-dihydro-2-oxazolyl)­benzene (IAox). The BP-C8, having two pyrrolidone rings, is obtained via a bulk aza-Michael addition reaction of 1,8-diaminooctane with 2 equiv of itaconic acid using water as catalyst. Thermosets are prepared by mixing the desired ratio of BP-C8 with IAox, followed by thermal curing at 180 °C. The cross-link density of the thermosets is controlled by the usage of an excess of bis­(2-oxazoline), and achievement of full conversion is confirmed by Fourier transform infrared spectroscopy. As anticipated, the glass transition temperature of the thermosets increases with increasing cross-linking density to values up to 100 °C. All thermosets are found to absorb water upon storage, resulting in a strong plasticizing effect and thus a suppression of the glass transition temperature. To assess the role of water on the thermo-mechanical properties, all thermosets are exposed to various relative humidities and their mechanical performance is evaluated. In general, we observe that the suppression in T g under the influence of water facilitates a brittle-to-ductile transition as the T g of the thermosets approaches room temperature. Additionally, in this study we demonstrate that hydrolysis of the ester bonds in the thermosets can be enforced at elevated temperatures in the presence of water, resulting in the liberation and migration of BP-C8 monomer. Interestingly, BP-C8 can readily be isolated by filtration as it crystallizes from water during cooling, thereby providing a promising route for its chemical recycling. Overall, these findings indicate that water plays a pivotal role in these poly­(ester–amide)­s as it functions as a catalyst in the BP-C8 synthesis, governs the thermal and mechanical properties of the thermosets, and opens up routes for chemical recycling of BP-C8 after hydrolysis as it acts as a recrystallization (co)­solvent.

Here we report on the influence of an aliphatic oxalamide-based nucleating agent (OXA3,6) on the viscoelastic and mechanical properties of isotactic polypropylene (iPP) blended with ultrahigh molecular weight iPP (UHMWiPP). The linear viscoelastic properties are investigated by using a plate−plate rheometer; the presence of only 0.5 wt % of OXA3,6 in the iPP−UHMWiPP blends results in a reduction of the complex viscosity in the entire frequency domain examined. This observation holds irrespective of the UHMWiPP weight fraction, up to 25 wt %. The viscosity suppression is attributed to an acceleration of the reorientation times of the chains, especially the longer ones, due to partial alignment of their molecular segments. Furthermore, SAXS measurements on cooled, injection molded samples hint that OXA3,6-containing samples display enhanced alignment under processing conditions (injection molding). Compared to samples without OXA, an increase in the SAXS intensity along the equator is observed in the OXA3,6 samples, implying an enhanced ability of shish-kebab formation. Such a morphological development results in higher yield stress while maintaining the elastic behavior.

In this work, we report on the small scale polycondensation and consecutive analysis of novel polyesters based on the potentially renewable 1,3-cyclopentanediol (CPdiol).