Effective Nucleating Agent Research Articles

Polyvinylidene fluoride/maghnite nanocomposites: fabrication and study of structural, thermal and mechanical properties

Abstract An in-depth study of polyvinylidene fluoride (PVDF) based nanocomposite systems will be the focus of this research. This polymer being hydrophobic and apolar, it will be unlikely to generate strong interactions with clay leaves called organophilic maghnite. The challenge of this study will therefore be to manage the load/polymer interfaces by using montmorillonite with specific surface treatments by adding a surfactant Cetyltrimethylammonium bromide. Therefore, a significant improvement in mechanical and thermal properties was observed. The properties of PVDFNC nanocomposites were evaluated using various physico-chemical techniques (XRD, FTIR, TGA, DSC, TEM, SEM). The results of the structural and thermal measurements carried out on these products reveal that the structural concept of the surfactant influences both the morphological profile, the thermal and mechanical properties of the nanocomposites obtained. Accelerated crystallization is observed in PVDNC nanocomposites as an effective nucleation agent, the crystals formed are predominantly β shaped and have a small number of polar α crystals. Measurements by X-ray diffraction, as well as transmission and scanning electron microscopy indicated that modified maghnite was perfectly distributed 3 % by weight in the polyvinylidene fluoride matrix. The mechanical properties of the nanocomposites were evaluated according to the filler material used and the polyvinylidene fluoride matrix.

CeO2 Protective Material against CMAS Attack for Thermal–Environmental Barrier Coating Applications

Calcium–magnesium–alumina–silicate (CMAS) attack is a crucial issue for thermal–environmental barrier coatings (T/EBCs) with the ever-increasing operating temperature of turbine engines. In this study, CeO2 has been demonstrated as a promising protective material for T/EBCs against CMAS attack. At 1300 °C, CeO2 powder kept excellent phase and structural stability in molten CMAS; there were some CMAS constituents dissolved into the CeO2 lattice to form a solid solution. With higher CeO2 contents and longer duration time, more CeO2 solid solution particles were formed, which acted as the nucleating agent for CMAS crystallization. As a result, apatite, anorthite and wollastonite crystalline products were easily generated. At 1300 °C for 10 h, CeO2 pellets covered with CMAS powder had limited degradation, which was attributed to the rapid crystallization of molten CMAS due to the excellent nucleating agent effect of the precipitated CeO2 solid solution.

Effects of self‐assembled nucleating agent on the crystallization behavior, thermal properties, and mechanical properties of polylactic acid

AbstractPolylactic acid (PLA) is a biodegradable polyester, but its low crystallization rate and excessive embrittlement limit its application. Decanedioic acid 1,10‐bis (2‐benzoylhydrazide) (TMC‐300) as an effective nucleating agent of PLA will induce PLA epitaxial crystallization and improve the crystallization rate of PLA. This article studied the promoting behavior of TMC‐300 with different contents in composite systems on PLA crystallization. The results showed that with the increase of TMC‐300 content, the crystallinity can be significantly increased, up to 22 times, and t1/2 significantly decreases. Meanwhile, with the addition of TMC‐300, the typical spherical crystal morphology of PLA gradually became attached to TMC‐300 fibrous crystal morphology. In terms of mechanical properties, the tensile strength reached its maximum at 0.5 wt% of TMC‐300 content, increasing from 60.60 MPa (PLA) to 74.59 MPa (0.5‐TMC‐300), an increase of 23.09%. At this time, due to the reduction in spherical crystal size, the elongation at break also increased significantly. However, the thermal stability of PLA composites deteriorated with the increase of nucleating agent content due to the low thermal decomposition temperature of TMC‐300 itself, and the Tmax decreased from 372°C (PLA) to 353°C (5‐TMC‐300), a decrease of 19°C.

Effect of Shear Stress during Processing on Structure, Morphology, and Properties of Isotactic Polypropylene Nucleated with Silsesquioxane-Based β-Nucleating Agent.

The study aimed to determine the influence of shear stress during real-life industrial processes such as compression molding and injection molding to different cavities on the crystallization of the isotactic polypropylene nucleated with a novel silsesquioxane-based β-nucleating agent. Octakis(N2,N6-dicyclohexyl-4-(3-(dimethylsiloxy)propyl)naphthalene-2,6-dicarboxamido)octasilsesquioxane (SF-B01) is a highly effective nucleating agent (NA) based on the hybrid organic-inorganic silsesquioxane cage. The samples containing various amounts of the silsesquioxane-based and commercial iPP β-nucleants (0.01-0.5 wt%) were prepared by compression molding and injection molding, including forming in the cavities with different thicknesses. The study of the thermal properties, morphology, and mechanical properties of iPP samples allows for obtaining comprehensive information about the efficiency of silsesquioxane-based NA in shearing conditions during the forming. As a reference sample, iPP nucleated by commercial β-NA (namely N2,N6-dicyclohexylnaphthalene-2,6-dicarboxamide, NU-100) was used. The static tensile test assessed the mechanical properties of pure and nucleated iPP samples formed in different shearing conditions. Variations of the β-nucleation efficiency of the silsesquioxane-based and commercial nucleating agents caused by shear forces accompanying the crystallization process during forming were evaluated by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). The investigations of changes in the mechanism of interactions between silsesquioxane and commercial nucleating agents were supplemented by rheological analysis of crystallization. It was found that despite the differences in the chemical structure and solubility of the two nucleating agents, they influence the formation of the hexagonal iPP phase in a similar way, taking into consideration the shearing and cooling conditions.

Novel, solvent‐based method for the production of polymer sheets with a superhydrophobic surface

AbstractWe have introduced a novel solvent‐based method to roughen polymer surfaces and characterized treated polypropylene (PP). The method consists of three main steps: solvent treatment, drying, and peeling. We investigated the effects of process parameters such as time of immersion in the solvent, solvent temperature, and drying temperature on the surface morphology created. The structure formed on the surface is mainly influenced by solvent temperature and drying temperature. We also characterized the wetting behavior of the surfaces. The patterned surfaces exhibit superhydrophobic characteristics with a high water contact angle (CA) (>155 °) and low water contact hysteresis (<5°). Adding an effective nucleating agent to PP makes it possible to generate outstanding CAs (>160°) and tailor spherulite sizes. The method is simple and scalable, therefore this superhydrophobic material is easy to mass‐produce.

Crystallization Kinetics of Modified Nanocellulose/Monomer Casting Nylon Composites.

Polyisocyanate and caprolactone were used to chemically functionalize nanocellulose (CNF). Composites of CNF, caprolactone-modified nanocellulose (CNF-CL) and polyisocyanate-modified nanocellulose (CNF-JQ)/MC nylon were fabricated by anionic ring-opening polymerization. The effects of the crystal structure, crystal morphology and crystallization process of MC nylon composites have been characterized by wide-angle X-ray diffraction (WAXD), polarized optical microscopy(POM) and differential scanning calorimetry (DSC). Isothermal crystallization kinetics were analyzed using the Avrami equation, and the crystallization rate, half-time, and Avrami exponent were calculated. The results show that the nucleation effects of CNF-JQ/MC nylon composites is increased with the CNF-JQ increase, and it is best compared with MC nylon, CNF/MC nylon and CNF-CL/MC nylon composites, so CNF-JQ can play the role of effective nucleating agent in MC nylon. We also discussed the non-isothermal crystallization of the composites. Analysis of the Jeziorny and Mo model demonstrates that the Zc values of CNF, CNF-CL, CNF-JQ/MC nylon composites increase, and the F(T) values decrease in order. This indicates that CNF-JQ can better promote the crystallization rate of non-isothermal crystallization of MC nylon. The results of this work demonstrate that CNF-JQ can be an effective nucleation agent and increase the crystallization rate of MC nylon compared with CNF-CL. The activation energy of the composites was studied using the kissing method, and the results showed that CNF-CL decreased the activation energy of MC nylon, and CNF and CNF-JQ increased the activation energy of MC nylon.

Polylactide/poly[(R)‐3‐hydroxybutyrate] (PHB) blend fibers with superior heat‐resistance: Effect ofPHBon crystallization

AbstractBlending low content of poly[(R)‐3‐hydroxybutyrate‐co‐4‐hydroxybutyrate] (P34HB ≤8 wt %) with poly(L‐lactide) (PLLA) has proven effective in enhancing heat resistance of PLLA fibers. Unfortunately, the enhancement is relatively limited with boiling water shrinkage of PLLA/P34HB blend fibers reduced to 9.9% at most. In this study, a series of PLLA/poly[(R)‐3‐hydroxybutyrate] (PHB) blend fibers with low PHB content (≤8 wt %) was prepared with sound spinnability. Surprisingly, the PLLA/PHB blend fibers showed much lower boiling water shrinkage than the PLLA/P34HB blend fibers with the same blend ratio. In particular, the boiling water shrinkage was dropped from ca. 80% for neat PLLA fibers to 9.9% for the PLA/P34HB blend fibers and further to 3.8% for the PLA/PHB blend fibers with 8 wt % P34HB or PHB added. Such an exceptionally improved heat resistance of the PLLA/PHB blend fibers could be closely related to an increase in crystallinity (Xc,PLLA) of the PLLA phase. Specifically, the mobility of the PLLA segments was promoted in the presence of PHB, along with notably improved orientation of the PLLA phase in the PLLA/PHB blend fibers. More importantly, investigation on crystallization behaviors revealed that the PHB phase served as an effective nucleating agent to accelerate the overall crystallization of PLLA. By contrast, the P34HB phase only acted as spherulite growth‐accelerating and/or nucleation‐assisting agents. These findings help provide a facile and effective strategy to improve heat resistance of PLLA fibers more significantly.

Crystallization and mechanical property of fully biobased poly(hexamethylene 2,5-furandicarboxylate)/cellulose nanocrystals composites

Through a common solution and casting method, novel fully biobased poly(hexamethylene 2,5-furandicarboxylate) (PHF)/cellulose nanocrystals (CNC) composites were prepared in this research at low contents of CNC. Scanning electron microscopy result showed that CNC uniformly dispersed in the PHF matrix without obvious aggregations, even CNC content reached 1 wt%. CNC, as a relatively effective heterogeneous nucleating agent, promoted the melt crystallization of PHF under different conditions. In addition, to explore the nucleation effect, the nucleation activity as well as the nucleation efficiency of CNC were quantitively determined. In the composites, the crystallization mechanism and crystal structure of PHF remained unchanged despite the presence of CNC. Low loadings of CNC improved both the Young's modulus and the yield strength of PHF to some degree, indicating that CNC nanofiller reinforced PHF matrix. In sum, CNC improved both the crystallization and the mechanical property of PHF, favoring the potential wider application of PHF/CNC composites due to the fully biobased feature.

Optimum processing conditions for the maximum crystallization rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

The effect of thermal and shear histories on the crystallization rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) was studied. As with other crystalline polymers, the shear history greatly affected the crystallization rate when the shear rate was beyond a critical value, i.e., the inverse of the Rouse relaxation time. Even after the formation of extended chain crystals, spherulite texture was clearly discernable. It grew from certain points on the extended chain crystals. Consequently, a row of spherulites appeared along the flow direction. The resin temperature in the molten state was also significant. When the sample was heated to 170 °C, which is beyond the main melting peak in the differential scanning calorimetry curve, unmolten crystals did not affect the linear viscoelastic properties. They acted as effective nucleating agents for the rest of the polymer during cooling. Therefore, the shear history hardly affected the crystallization rate and the number of spherulites.

How nucleating particles migration affects the fractionated crystallization of isotactic polypropylene/polystyrene immiscible blends

We investigate the inter-phase migration of nucleating particles and their effect on the fractionated crystallization of polypropylene droplets dispersed in an immiscible polystyrene matrix by preparing melt-mixed 90/10 wt% PS/PP blends with selected nucleating agents. Different concentrations of nucleating agents (NAs): Phtalocianene Blue, NA11, Talc, and sodium benzoate, were initially incorporated either in neat PP or in neat PS. Then the different PS/PP/NAs blends were prepared. Contact angles were determined for the neat polymers and the NAs, and the results indicated that, from a thermodynamics point of view, all NAs should remain or migrate to the PS phase. According to SEM observations, a sea-island morphology was obtained that did not vary with NA addition. Hence the results should be independent of differences in the morphology.PP droplets crystallized in neat blends in three well-differentiated crystallization peaks (i.e., fractionated crystallization). The NAs induce a concentration-dependent increase in the high-temperature crystallization peak at the expense of reducing the low-temperature peaks, as droplets become in contact with or contain the NAs. When compared at a constant concentration in one of the phases, the nucleating agents have efficiencies that decrease in the order: Pht Blue ≈NA11>Talc>Sod Benz. Surprisingly, for the three most effective NAs, it was found that adding them initially to the PS phase led to a much higher nucleation efficiency (evaluated in terms of increases in peak crystallization temperature) than adding them to PP. This indicates that these NAs, initially present in the PS phase, migrate to the interface or to the bulk of the PP phase (against thermodynamics). Sod Benz was the only exception, as it shows a higher thermodynamic affinity to the PS phase. We explain the migration of most particles from the PS phase to the phases’ boundary or to the bulk of the PP droplets by considering that kinetic factors dominate the behavior, as, from a rheological perspective, the minor component (PP) always displays a lower viscosity than the matrix component (PS) under the chosen mixing conditions.

Renewable rice straw cellulose nanofibril reinforced poly(ε-caprolactone) composite films

In this study, cellulose nanofibrils (CNFs) fabricated from rice straw were utilized to reinforce poly(ε-caprolactone) (PCL), and the structure and properties of these CNF/PCL composite films were analyzed by morphology observation and the measurements of X-ray diffraction (XRD), differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), mechanical property and water absorption. The experimental results revealed that in PCL matrix, CNF exhibits a homogeneous distribution at low content, but shows some aggregates at high content. The incorporated CNF doesn't change the crystal type, crystallinity and melting temperature of PCL, but accelerates the crystallization of PCL due to its heterogeneous nucleating agent effect. Compared with PCL film, the CNF/PCL composite films show obvious improvement of tensile strength and Young's modulus with the increments of 7.5% at 10% CNFs and 76% at 15% CNFs respectively. However, after the CNF content exceeds 10%, the tensile strength of the composite films begins to decrease, and high loading of CNFs also causes remarkable negative influences on the thermal stability and hydrophobicity of the composite films. The straw CNFs reinforced PCL composite films can be employed in packaging and biomedical applications.

Enhancement in Crystallizability of Poly(L-Lactide) Using Stereocomplex-Polylactide Powder as a Nucleating Agent.

High-molecular-weight poly(L-lactide) (HMW-PLLA) is a promising candidate for use as a bioplastic because of its biodegradability and compostability. However, the applications of HMW-PLLA have been limited due to its poor crystallizability. In this work, stereocomplex polylactide (scPLA) powder was prepared by precipitation of a low-molecular-weight poly(L-lactide)/poly(D-lactide) (LMW-PLLA/LMW-PDLA) blend solution and investigated for use as a fully-biodegradable nucleating agent for HMW-PLLA compared to LMW-PLLA powder. The obtained LMW-PLLA and scPLA powders with a nearly spherical shape showed complete homo- and stereocomplex crystallites, respectively. HMW-PLLA/LMW-PLLA powder and HMW-PLLA/scPLA powder blends were prepared by melt blending. The LMW-PLLA powder was homogeneously melted in the HMW-PLLA matrices, whereas the scPLA powder had good phase compatibility and was well-dispersed in the HMW-PLLA matrices, as detected by scanning electron microscopy (SEM). It was shown that the enthalpies of crystallization (ΔHc) upon cooling scans for HMW-PLLA largely increased and the half crystallization time (t1/2) dramatically decreased as the scPLA powder content increased; however, the LMW-PLLA powder did not exhibit the same behavior, as determined by differential scanning calorimetry (DSC). The crystallinity content of the HMW-PLLA/scPLA powder blends significantly increased as the scPLA powder content increased, as determined by DSC and X-ray diffractometry (XRD). In conclusion, the fully biodegradable scPLA powder showed good potential for use as an effective nucleating agent to improve the crystallization properties of the HMW-PLLA bioplastic.

Coupled effect of self-assembled nucleating agent, Ni-CNTs and pressure-driven flow on the electrical, electromagnetic interference shielding and thermal conductive properties of poly (lactic acid) composite foams

Biobased and biodegradable poly (lactic acid) (PLA) composite foams with good mechanical properties, a low percolation threshold, and absorption-dominant shielding properties with little reflection are considered suitable substitutes for traditional petroleum-based polymer composite foams in various applications. However, fabricating PLA composite foams that simultaneously satisfy all the above properties remains a significant challenge, particularly at low conductive filler addition. In this study, we successfully fabricated high-performance multifunctional PLA/self-assembled nucleating agent (TMC-306)@Ni-CNTs composite foams. In the ternary composites system, PLA and 0.5 wt% TMC-306 were melt mixed first to prepare granules and used as a polymer matrix, while Ni-CNTs were employed as a conductive segregated filler. To determine the coupled effect of TMC-306, Ni-CNTs, and pressure-driven flow on PLA composite foams, rheological, crystallization, and morphological properties of ternary composites were initially investigated. The results demonstrated that the increased complex viscosity of composites with increasing Ni-CNTs content affected the flow orientation under pressure-driven flow and the pore growth of the subsequent foaming process. The low content of Ni-CNTs could play a synergistic role with TMC-306 to improve PLA crystallization ability, whereas the nucleating agent effect was inhibited at high Ni-CNTs content. Additionally, pressure-driven flow induced the formation of segregated oriented conductive networks and ordered crystalline structures in the matrix, which significantly impacted on the low-temperature foaming performance of PLA composites. After supercritical carbon dioxide (Sc-CO2) foaming treatment, the composite foams exhibited an ultralow percolation threshold of 0.076 vol% and high electrical conductivity of 7.58 × 10−2 S/cm at an ultralow Ni-CNTs content of 0.805 vol%. Moreover, the composite foams containing 0.805 vol% Ni-CNTs achieved a high electromagnetic interference (EMI) shielding effectiveness (SE) of 25.2 dB and an absorption-dominant shielding mechanism with a high absorptivity of 86%. It also had a low density of 0.36 g/cm3, a high compressive strength of 5.42 MPa and a good thermal conductivity of 62.3 mW·m−1·K−1. In summary, this study may provide a facile and cost-effective strategy for developing high-performance PLA composite foams with broad applications.

Epoxy chain extender grafted pyrophyllite/poly(ethylene terephthalate) composites with enhanced crystallinity and mechanical properties

AbstractThe surface‐grafting modification of nano clay has become increasingly important for improving the practical application of clays. In this study, an epoxy chain extender ADR‐4468 was used to modify the surface of pyrophyllite (Prl), and the effect of ADR‐4468‐modified pyrophyllite (A‐Prl) on the properties of poly(ethylene terephthalate) (PET) and PET/poly(ethylene glycol‐co‐1,3/1,4‐cyclohexanedimethanol terephthalate) (PETG) composites was investigated. The modified composites were characterized by Fourier transformed infrared spectroscopy, X‐ray diffraction and TG, which proved that the A‐Prl was successfully synthesized, and the addition of ADR‐4468 did not change the crystal structure of pyrophyllite. The grafted ADR‐4468 improved the agglomeration of Prl, and some A‐Prl reached nano‐scale dispersion in PET and PET/PETG composites. The rheological properties, crystallization behavior and mechanical properties of PET and PET/PETG nanocomposites were systematically investigated. The results showed that A‐Prl was an effective nucleating agent for PET, which significantly improved the crystallization properties of PET composites. The A‐Prl also improved the comprehensive mechanical properties of PET and PET/PETG nanocomposites. In particular, the impact toughness of A‐Prl/PET/PETG composite with 1.5 wt % A‐Prl was increased by 120% compared with that of pure PET. The functional additive is expected to be used in the preparation of high‐performance and recyclable PET composites.

Molecular Dynamics Simulation of the Crystallization Behavior of Octadecane on a Homogeneous Nucleus

Latent heat storages have the ability to contribute to a more sustainable energy supply network. However, phase change materials (PCM) used for latent heat storages often show supercooling. This phenomenon takes place whenever the PCM begins crystallizing below the freezing point and is one of the biggest drawbacks holding back the widespread use of PCM. Nucleation agents (NA) can be used to avoid the supercooling, yet the choice of an effective NA is not straightforward. In this work, molecular dynamics (MD) simulation was tested in order to simulate the crystallization of Octadecane on a NA. The simulation results include density, phase change temperature and enthalpy as well as the crystal structure and lie in good agreement with literature values and the authors’ own experimental data. Further simulations of the crystallization process on different surfaces of homogeneous nuclei acting as a NA were performed. The results reflect the hypothesis that liquid molecules start crystallizing easier on surfaces exposing the whole chain side rather than the chain ends. With the result, that the choice of parameters for the MD simulation represent the Octadecane system reliably and further studies can be performed including heterogeneous NA.

The influence of nucleating agents, plasticizers, and molding conditions on the properties of injection molded PLA products

Poly(lactic acid) (PLA) is a “green” alternative to petroleum-based plastics and a desirable choice for many applications. However, low heat deflection temperature and lack of toughness, together with the slow crystallization kinetic of neat PLA hinder its widespread application. The weak properties of PLA can be improved with the improvement of crystallinity, which depends on molecular weight, D-lactide content, the presence of different modifiers and the processing conditions. We aimed to maximize the crystallinity and crystallization rate of PLA to explore the limitations of PLA when it is processed by injection molding. Therefore, we selected PLA with low D-lactide content, the three effective nucleating agents and the two suitable plasticizers. We found that the heat deflection temperature, tensile strength, and Young’s modulus of PLA modified with nucleating agents were considerably better than those of Acrylonitrile Butadiene Styrene (ABS). However, the elongation at break of the annealed and the simultaneously nucleated and plasticized PLA compounds was significantly lower than that of ABS. The addition of nucleating agents and plasticizers and the variation of mold temperature did not improve the brittleness of PLA. The elongation at break of PLA was still very low and stayed in the 1.7–2.5% range.

Dual effect of ZrO2 on phase separation and crystallization in Li2O–Al2O3–SiO2–P2O5 glasses

AbstractZrO2 is an effective nucleation agent for low‐expansion lithium–aluminum silicate (LAS) glass–ceramic (GC) with high Al2O3 content. However, the effect of ZrO2 is still not fully understood in LAS glasses with low contents of Al2O3 and P2O5. In this work, the effect of ZrO2 on the phase separation and crystallization of Li2O–Al2O3–SiO2–P2O5 glasses were investigated. The results revealed that ZrO2 significantly increased Tg and the crystallization temperature of Li2SiO3 and Li2Si2O5 crystals. Li3PO4 crystals precipitated preferentially in the glass containing 3.6‐mol% ZrO2, wherein Zr was stable in the network and no precipitation of ZrO2 nanocrystals was observed. Moreover, the separation of phosphate‐rich phases in the as‐quenched glasses increased with the addition of ZrO2. The findings of the study revealed a dual role of ZrO2. First, ZrO2 acted as a glass network former rather than a nucleation agent, increasing glass viscosity and the nucleation barrier of Li2SiO3 through its strong network connectivity. Second, as Zr preferentially combined with non‐bridging oxygen to form Si–O–Zr linkages, a sufficient amount of charge‐balancing Li+ ions existed in the network, which promoted the separation of phosphate‐rich phases. It indicated that the incorporation of ZrO2 contributes to the activation of the nucleation role of P2O5, thus contributing to the formation of nanocrystals and fine microstructure of GCs.

Functionalized carbon nanotubes for 3D-printed PLA-nanocomposites: Effects on thermal and mechanical properties

PLA-based nanocomposites are of great interest to biomedical applications due to the biocompatibility and biodegradability of the Poly (lactic acid) (PLA), being, therefore, widely explored for application in additive manufacturing by fused filament fabrication (FFF). In this context, carbon nanotubes (CNT) have been an attractive additive to improve the mechanical strength of 3D printed PLA parts. However, a good dispersion of the CNT in the PLA matrix is essential to guarantee that it acts as a reinforcing material. Functionalized carbon nanotubes are able to increase the dispersibility and interaction of carbon nanotubes with polymers. Nonetheless, there is very limited information available about the incorporation of functionalized CNT in 3D printed PLA parts produced by FFF. In this study, CNT functionalization was performed with HNO3 solution to create defects and incorporate oxygen functional groups on the CNT surface in order to evaluate its influence on thermal and mechanical properties of 3D-printed PLA/CNT nanocomposites. The results indicated that functionalized CNTs (f-CNT) presented a better dispersion in the matrix and act as more effective nucleating agents for PLA crystallization, when compared with the use of commercial CNT (c-CNT). The addition of only 0.5 wt% of f-CNT was enough to provide a significant increase of the mechanical strength of the 3D printed parts (from 29.4 ± 0.7 MPa for PLA/c-CNT to 41.6 ± 1.4 MPa for PLA/f-CNT) and provide better interfacial adhesion between 3D printed layers, maintaining the thermal stability of the nanocomposites. Dynamic-mechanical analyses indicated a significant increase in the storage modulus (~ 43% at 37 °C) when f-CNT was used as reinforcement. Therefore, both thermal and mechanical properties of 3D-printed PLA/CNT nanocomposites were significantly improved when f-CNT were used, also indicating that percentages less than 1 wt% of this additive are required. Thus, the use of these nanocomposites to produce medical devices by FFF, for example, can be potentialized.

Poly (L-lactic acid) Modified by N, N -bis(Stearic acid)-1,4-Dicarboxybenzene Dihydrazide: Studies of Crystallization, Melting Behavior and Thermal Decomposition

In this study, a new organic nucleating agent N, N -bis(stearic acid)-1,4-dicarboxybenzene dihydrazide (PASH) to improve crystallization behavior of poly(L-lactic acid) (PLLA) along with the effect of PASH on melting behavior, thermal stability of PASH-nucleated PLLA was holistically reported. The melt-crystallization process illustrated that PASH as an effective heterogeneous nucleating agent could boost PLLA�s crystallization rate, but increasing PASH concentration and cooling rate conversely inhibited melt-crystallization process of PLLA in this study. With respect to melt-crystallization process, a larger amount of PASH leaded to a shift of cold-crystallization peak to lower temperature level. Isothermal crystallization revealed, in comparison to pure PLLA, that the half time of overall crystallization of PLLA/PASH was significantly decreased with PLLA containing 3 wt% PASH having the minimum t1/2= 67.3 s at 105şC. The different melting behaviors of PLLA/PASH under different conditions were attributed to the nucleating effect of PASH within PLLA. In particular, the melting behavior at a heating rate of 10�C/min after isothermal crystallization depended primarily on the crystallization temperature. Whereas, the impact of crystallization time on melting behavior was negligible. Nonetheless, the melting behavior was influenced by the heating rate after non-isothermal crystallization. The thermal stability of PLLA was detrimental with the addition of PASH owing to a typical drop in onset thermal decomposition temperature.

Comparison of the efficiency of the most effective heterogeneous nucleating agents for Poly(lactic acid)

We selected the thirteen most effective nucleating agents for Poly(lactic acid) (PLA) from the literature, and synthesized and compounded them with two different PLA grades: 3001D (1.4% D-lactide content) and 3100HP (0.5% D-lactide content, considered PLLA). We determined the crystallinity and crystallization of PLA with different nucleating agents in identical conditions (same nucleating agent content, same cooling rate) with the help of differential scanning calorimetry. We compared the efficiency of each nucleating agent and found that for both PLA grades, Zinc PhenylPhosphonate was the most effective. However, even when nucleated PLA was injection molded into a cold mold (25 °C), it still could not fully crystallize during cooling and the heat deflection temperature did not increase significantly. The maximum achieved crystallinity, in this case, was between 32.4 and 35.7%. On the contrary, when a 90 °C “hot mold” and in-mold crystallization together were applied, the specimens achieved full crystallization during the injection molding cycle (crystallinity was between 44.5 and 50.0%), and the heat deflection temperature increased to an average of 88.8 °C. We also examined the mechanical properties of the nucleated PLA and found that the usage of nucleating agents together with a hot mold improved tensile strength, tensile modulus, and Charpy impact strength but decreased elongation at break.