Preparation and characterization of thermoplastic polyurethane/organoclay nanocomposites by melt intercalation technique: Effect of nanoclay on morphology,mechanical, thermal,and rheological properties

Nanocomposites based on thermoplastic polyurethane (TPU) and organically modified montmorillonite (OMMT) were prepared by melt blending. Organically modified nanoclay was added to the TPU matrix in order to study the influence of the organoclay on nanophase morphology and materials properties. The interaction between TPU matrix and nanofiller was studied by infrared spectroscopy. Morphological characterization of the nanocomposites was carried out using X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy techniques. The results showed that melt mixing is an effective process for dispersing OMMT throughout the TPU matrix. Nanocomposites exhibit higher mechanical and thermal properties than pristine TPU. All these properties showed an increasing trend with the increase in OMMT content. Thermogravimetric analysis revealed that incorporation of organoclay enhances the thermal stability of nanocomposites significantly. Differential scanning calorimetry was used to measure the melting point and the glass transition temperature (T_g) of soft segments, which was found to shift toward higher temperature with the inclusion of organoclays. From dynamic mechanical thermal analysis, it is seen that addition of OMMT strongly influenced the storage and loss modulus of the TPU matrix. Dynamic viscoelastic properties of the nanocomposites were explored using rubber process analyzer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of thermoplastic polyurethane on the properties of poly(lactic acid)/organo‐montmorillonite nanocomposites based on novel vane extruder

Polylactic acid (PLA)/organo‐montmorillonite (OMMT) nanocomposites toughened with thermoplastic polyurethane (TPU) were prepared by melt‐compounding on a novel vane extruder (VE), which generates global dynamic elongational flow. In this work, the mechanical properties of the PLA/TPU/OMMT nanocomposites were evaluated by tensile, flexural, and tensile tests. The wide‐angle X‐ray diffraction and transmission electron microscopy results show that PLA/TPU/OMMT nanocomposites had clear intercalation and/or exfoliation structures. Moreover, the particles morphology of nanocomposites with the addition of TPU was investigated using high‐resolution scanning electronic microscopy. The results indicate that the spherical TPU particles dispersed in the PLA matrix, and the uniformity decreased with increasing TPU content (≤30%). Interestingly, there existed abundant filaments among amount of TPU droplets in composites with 30 and 40 wt% TPU. Furthermore, the thermal properties of the nanocomposites were examined with differential scanning calorimeter and dynamic mechanical analysis. The elongation at break and impact strength of the PLA/OMMT nanocomposites were increased significantly after addition of TPU. Specially, Elongation at break increased by 30 times, and notched impact strength improved 15 times when TPU loading was 40 wt%, compared with the neat PLA. Overall, the modified PLA nanocomposites can have greater application as a biodegradable material with enhanced mechanical properties. POLYM. ENG. SCI., 54:2292–2300, 2014. © 2013 Society of Plastics Engineers     

Mechanically adaptive thermoplastic polyurethane/cellulose nanocrystal composites: Process-driven structure–property relationships

To enable filament extrusion additive manufacturing of mechanically adaptive nanocomposites, the effect of melt extrusion on the tensile modulus and mechanical adaptiveness of cellulose nanocrystal (CNC)/thermoplastic polyurethane (TPU) composites was investigated. TPU (Texin RxT70A) was processed with 10 wt % CNC in multiple formats, including solvent-cast films and melt extrusion-produced filaments. CNC orientation is characterized by polarized Raman spectroscopy and small-angle X-ray scattering (SAXS) and found to be uniaxially oriented in extruded filaments, and randomly oriented in solvent-cast films. Dynamic mechanical analysis results show the addition of 10 wt % CNC increases the pure TPU storage modulus from 10 to 60–70 MPa in the dry state for solvent-cast and extruded nanocomposites. Following water saturation, all CNC-containing samples reach a similar wet storage modulus of approximately 26 MPa, regardless of CNC orientation and thermal history. Fickian diffusion scaling factors (6.8 to 11.6) scale closely to the time-dependent empirical scaling factors (4.9 to 7.2), confirming the rate of mechanical adaptivity is driven by water diffusion through sample thickness. Our results suggest that mechanical adaptivity is retained following processing, enabling use as a feedstock for extrusion-based additive manufacturing of CNC/TPU composites for mechanically adaptive parts. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46992.     

Electrical and rheological percolation in poly(vinylidene fluoride)/multi‐walled carbon nanotube nanocomposites

Nanocomposites of poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWCNTs) were prepared through melt blending in a batch mixer (torque rheometer equipped with a mixing chamber). The morphology, rheological behavior and electrical conductivity were investigated through transmission electron microscopy, dynamic oscillatory rheometry and the two‐probe method. The nanocomposite with 0.5 wt% MWCNT content presented a uniform dispersion through the PVDF matrix, whereas that with 1 wt% started to present a percolated network. For the nanocomposites with 2 and 5 wt% MWCNTs the formation of this nanotube network was clearly evident. The electrical percolation threshold at room temperature found for this system was about 1.2 wt% MWCNTs. The rheological percolation threshold fitted from viscosity was about 1 wt%, while the threshold fitted from storage modulus was 0.9 wt%. Thus fewer nanotubes are needed to approach the rheological percolation threshold than the electrical percolation threshold. Copyright © 2010 Society of Chemical Industry     

Effect of annealing treatment on the structure and properties of polyurethane/multiwalled carbon nanotube nanocomposites

The thermoplastic polyurethane/multiwalled carbon nanotube (TPU/CNT) nanocomposites with high conductivity and low percolation threshold value were prepared by melting blending and annealing treatment. The effect of annealing process on the microphase structure and the properties of TPU/CNT nanocomposites was studied. It has been shown that CNT flocculation can occur in TPU/CNT nanocomposites during the annealing process. At a critical CNT content, which defined the percolation threshold, CNTs could form conductivity network. The conductive percolation threshold value of TPU/CNT nanocomposites was decreased from 10 to 4% after annealing process, and the conductivity of TPU/CNT nanocomposites with 10 vol % of CNT could reach 1.1 S/m after an annealing time of 1 h. The significant enhancement of electrical conductivity was influenced by the annealing time and the content of CNTs. The formation of CNT networks was also verified by dynamic viscoelastic characterization. The results of X‐ray diffraction and differential scanning calorimetry indicated that annealing process reinforced the microphase separation of the nanocomposites. Mechanical properties test showed that the annealing treatment was in favor of improving the mechanical properties; however, further increase in the annealing time has negative effect on the mechanical properties. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation, morphology, and ultra-low dielectric constants of benzoxazine-based polymers/polyhedral oligomeric silsesquioxane (POSS) nanocomposites

Nanocomposites of benzoxazine-based polymers/polyhedral oligomeric silsesquioxane (POSS) have been prepared through copolymerization of furan-containing benzoxazine compounds and methylmethacrylate-POSS (MMA-POSS). Nanocomposites having MMA-POSS fractions of 0-70 wt% (POSS fractions of 0-28 wt%) are obtained. The high contents of MMA-POSS of the nanocomposites result in a reduction of their dielectric constants to 2.3. Moreover, some nanocomposites display POSS orientation into lamellar structures in nanometer sizes. The POSS orientation further reduces the dielectric constants of the nanocomposites to about 1.9. Hence, the prepared nanocomposites could be used as ultra-low-k materials for advanced microelectronics.     

Economical conductive graphite-filled polymer composites via adjustable segregated structures: Construction,low percolation threshold,and positive temperature coefficient effect

The economical graphite-filled thermoplastic urethane/ultra-high molecular weight polyethylene (TPU/UHMWPE) composites with the segregated structure were constructed by the combination of mechanical crushing and melt blending method. The low percolation threshold of 1.89 wt% graphite in the adjustable segregated composites was obtained and high electrical conductivity was about 10⁻¹ S m⁻¹ at 10 wt% graphite loadings owing to the formation of three-dimensional conductive networks. Moreover, when the graphite loadings were over the percolation threshold, the remarkable positive temperature coefficient (PTC) effect of electrical resistivity for TPU/UHMWPE-Graphite composites were achieved, originating from the combined thermal motion of TPU and UHMWPE. Meanwhile, the outstanding repeatability of PTC effects was obtained after 5-time cycles. Therefore, economical conductive polymer composites were still the promising field in the practical application of PTC materials.     

Montmorillonite–multiwalled carbon nanotube nanoarchitecture reinforced thermoplastic polyurethane

Montmorillonite (MMT)–multiwalled carbon nanotube (MWCNT) hybrids were prepared in different weight ratios by simple dry grinding method and characterized. Subsequently, MMT–MWCNT (1:1) hybrid was used as reinforcing filler in developing thermoplastic polyurethane (TPU) nanocomposites by solution blending method. Thermogravimetric analysis showed that 0.25 wt% hybrid‐loaded TPU nanocomposite exhibited maximum enhancement of 31°C corresponding to 50 wt% loss in thermal stability when compared with neat TPU. Differential scanning calorimetry of this composite also indicated that its crystallization and melting temperatures are enhanced by 37 and 13°C, respectively. Mechanical data showed that tensile strength and Young's modulus of 0.50 wt% filled TPU were maximum improved by 57 and 87.5%, respectively. Dynamic mechanical analysis (DMA) measurements indicated 174% (50°C) improvement in storage modulus of 0.50 wt% hybrid‐loaded TPU. Such improvements in thermal and mechanical properties have been attributed to homogeneous dispersion, strong interfacial interaction, and synergistic effect. POLYM. COMPOS., 37:1775–1785, 2016. © 2014 Society of Plastics Engineers     

Mechanical and thermal properties of thermoplastic polyurethane‐toughened polylactide‐based nanocomposites

The crystallinity and mechanical and thermal properties of polylactide (PLA)‐based biodegradable‐engineered plastic nanocomposites were determined. The nanocomposites were composed of thermoplastic polyurethane (TPU)‐toughened PLA, Talcum (Talc) and organic modified clay (montmorillonite; OMC). The tensile and flexural tests showed that PLA blended with 10 wt% TPU, 4 wt% Talc powder and 2 wt% OMC had the highest modulus and strength without a loss of elongation. The heat distortion temperature (HDT) tests demonstrated that the thermally treated PLA‐based nanocomposites had an HDT of nearly double the HDT for untreated specimens. An analysis of the polymer using scanning electron microscopy demonstrated that the incorporation of inorganic fillers altered the heterogeneous morphology of the PLA/TPU blend. This study investigated the feasibility of using PLA‐based nanocomposites for practical use, including applications in the automotive and furniture industries. POLYM. COMPOS., 35:1744–1757, 2014. © 2013 Society of Plastics Engineers     

Influence of annealing-induced phase separation on the shape memory effect of graphene-based thermoplastic polyurethane nanocomposites

Thermoplastic polyurethane (TPU) is a multiblock copolymer that exhibits an attractive shape memory effect (SME). Its morphology consists of a soft segment (SS), which corresponds to the polyol or a long-chain diol, while the hard segment involves the intercalation of a diisocyanate and a chain extender. Due to the distinct thermodynamic parameters of each monomer, these segments are not miscible with each other, resulting in a phase-separated structure in their morphology. This structure is characterized by the formation of soft and hard domains (SD and HD), respectively. When incorporating 0.1 wt% of graphene nanoplatelets (GNP) or 0.1 wt% of multilayer graphene oxide (mGO) into the TPU matrix using solution casting process, a contribution to the phase separation of these domains is observed. This phenomenon becomes even more pronounced when graphene-based nanocomposites are subjected to annealing at 110°C for 24 hours, indicating a good interaction between the GO and GNP with the HD and SS, respectively. After annealing, the nanocomposites (TPU + GNP and TPU + mGO) exhibit improved performance in SME, as evidenced by an approximately 9% increase in the shape recovery ratio compared to the nonannealed TPU. Additionally, all nanocomposites maintained a high strain during SME programming, surpassing that of pure TPU, both before and after annealing. This suggests a direct influence of the graphene-based nanoparticles on the shape memory effect.     

Cellulose nanocrystal-mediated assembly of graphene oxide in natural rubber nanocomposites with high electrical conductivity

This study reports a green and powerful strategy for preparing cellulose nanocrystal (CNC)/graphene oxide (GO)/natural rubber (NR) nanocomposites hosting a 3D hierarchical conductive network. Due to good dispersibility and amphiphilic nature of CNC, well dispersed CNC/GO nanohybrids were prepared. Hydrogen bonding interactions between CNC and GO greatly enhanced the stability of the CNC/GO nanohybrids. CNC/GO nanohybrids were introduced into NR latex under sonication and the mixture was cast. Self-assembled CNC/GO nanohybrids preferentially dispersed in the interstice between latex microspheres allowing the construction of a 3D hierarchical conductive network. By combining strong hydrogen bonds and 3D conductive network, both electrical conductivity and mechanical properties (tensile strength and modulus) have been significantly improved. The electrical conductivity of the nanocomposite with 4 wt% GO and 5 wt% CNC exhibited an increase of nine orders of magnitude compared to the nanocomposite with only 4 wt% GO; meanwhile, the electrical percolation threshold was 3-fold lower than for NR/GO composites.     

Thermoplastic polyurethane nanocomposites of reactive silicate clays: effects of soft segments on properties

This paper addresses the effects of soft-segment on clay particle exfoliation and resultant mechanical and thermal properties of nanocomposites of reactive layered silicate clay and thermoplastic polyurethanes (TPU). The composites were synthesized via a two-step bulk polymerization scheme from polyether- and polyesterpolyols of molecular weight 2000, diphenylmethanediisocyanate, butanediol, and up to 5 wt% reactive layered silicate clay. It was found that the extent of tethering reactions between polymer chains carrying residual -NCO groups and reactive clay particles was significant, although did not depend on the nature of polyol used. Nanocomposites were obtained only in the case of polyesterpolyol, which can be attributed to both clay-polymer reactions and higher viscosity in the clay-polymer mixing step. These nanocomposites showed 125% increase in tensile stress, 100% increase in elongation, and 78% increase in tensile modulus along with 130% increase in tear strength and a 60% reduction in volume loss in abrasion test. It was observed that hydrogen bonding did not influence the properties and the extent of hydrogen bonding was not affected by the clay particles.     

Microphase separation and hard domain assembly in thermoplastic polyurethane/multiwalled carbon nanotube nanocomposites

We studied the role of multiwalled carbon nanotubes (MWCNTs) on microphase separation and hard domain assembly in the thermoplastic polyurethane/multiwalled carbon nanotube nanocomposites via combination of rheology and thermal analysis (DSC and DMA). The strong solid‐like response observed at low frequency together with very low rheological percolation threshold (0.15 wt%) shown by the samples at their disordered state temperature revealed great capability of TPU in dispersing MWCNTs. The results of microphase separation kinetics measured for the fast‐cooled samples using the time sweep experiments under isothermal condition together with thermal analysis showed a significant enhancing effect of MWCNTs on accelerating kinetics as well as promoting the extent of hard domain formation. These results could be attributed to increased thermodynamic incompatibility between hard and soft domain of TPU matrix as a result of greater affinity of MWCNTs with hard segments. This allowed the MWCNTs to act as attractive platforms for formation and assembly of hard domains. POLYM. ENG. SCI., 55:2163–2173, 2015. © 2015 Society of Plastics Engineers     

Polyurethaneurea–silica nanocomposites: Preparation and investigation of the structure–property behavior

Nanocomposites consisting of thermoplastic polyurethane–urea (TPU) and silica nanoparticles of various size and filler loadings were prepared by solution blending and extensively characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermal analysis, tensile tests, and nanoindentation. TPU copolymer was based on a cycloaliphatic diisocyanate and poly(tetramethylene oxide) (PTMO-2000) soft segments and had urea hard segment content of 20% by weight. TPU/silica nanocomposites using silica particles of different size (29, 74 and 215 nm) and at different loadings (1, 5, 10, 20 and 40 wt. %) were prepared and characterized. Solution blending using isopropyl alcohol resulted in even distribution of silica nanoparticles in the polyurethane–urea matrix. FTIR spectroscopy indicated strong interactions between silica particles and polyether segments. Incorporation of silica nanoparticles of smaller size led to higher modulus and tensile strength of the nanocomposites, and elastomeric properties were retained. Increased filler content of up to about 20 wt. % resulted in materials with higher elastic moduli and tensile strength while the glass transition temperature remained the same. The fracture toughness increased relative to neat TPU regardless of the silica particle size. Improvements in tensile properties of the nanocomposites, particularly at intermediate silica loading levels and smaller particle size, are attributed to the interactions between the surface of silica nanoparticles and ether linkages of the polyether segments of the copolymers.     

Effect of organoclay on the morphology,mechanical, thermal,and rheological properties of organophilic montmorillonite nanoclay based thermoplastic polyurethane nanocomposites prepared by melt blending

Polymer nanocomposites based on the thermoplastic polyurethane (TPU) and organically modified montmorillonite (OMMT) was prepared by melt intercalation technique using a laboratory internal batch mixer followed by compression molding. Varying amount of organically modified nanoclays (1, 3, 5, 7, and 9 wt%) was added to the TPU matrix to examine the influence of organoclay on nanophase morphology and structure–property relationships. The interaction between TPU matrix and nanofiller was studied by infrared spectroscopy. The morphology of nanocomposites was studied by X‐ray diffraction, transmission electron microscopy, and atomic force microscopy that shows melt mixing by a batch mixer is an effective method for dispersing OMMT throughout the TPU matrix. Thermogravimetric analysis revealed that incorporation of organoclay enhances the thermal stability of the nanocomposites significantly. Differential scanning calorimetry was employed to measure the melting point and glass transition temperature (T_g) of soft segments. The reinforcing effect of the organoclay was determined by dynamic mechanical analysis and physico–mechanical testing. The effects of nanoclay concentration and processing parameters on the dynamic viscoelastic properties of the nanocomposites were studied by a rubber process analyzer using frequency sweep. A significant increase in the viscosity and storage modulus of the nanocomposites was found with the increasing clay content. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Properties of na‐montmorillonite and cellulose nanocrystal reinforced poly(butyl acrylate‐co‐methyl methacrylate) nanocomposites

Poly(butyl acrylate‐co‐methyl methacrylate) (BA‐co‐MMA) nanocomposite latexes were synthesized in the presence of sodium montmorillonite (Na‐MMT) and cellulose nanocrystal (CNC) as fillers. Nanocomposite preparation with 3 wt% Na‐MMT based upon the total monomer amount was conducted by semi‐batch emulsion polymerization. Furthermore, direct blending of neat copolymer latex with Na‐MMT was performed for comparison. CNC/BA‐co‐MMA nanocomposites were obtained via blending process with varying CNC content (1, 2, and 3 wt %). Good dispersion of both Na‐MMT and CNC within the copolymer matrix was achieved as demonstrated by X‐ray diffraction and transmission electron microscope. Particle size of the nanocomposite latexes was around 120 nm. Thermal, mechanical, and barrier properties of the copolymer showed great improvement with the addition of both Na‐MMT and CNC. CNC nanocomposites displayed enhanced properties with increasing CNC level. Tensile strength of copolymer latex with 3 wt% CNC reached 262.5% of the pristine latex, while tensile strength of Na‐MMT nanocomposite at the same content was 187.5% of the pristine latex. POLYM. ENG. SCI., 55:2922–2928, 2015. © 2015 Society of Plastics Engineers     

A strategy of fabricating exfoliated thermoplastic polyurethane/clay nanocomposites via introducing maleated polypropylene

By reducing the attraction between the platelets of octadecylammonium chloride modified montmorillonite (OMMT-C18) via pre-intercalation of maleated polypropylene (MAPP), OMMT-C18 was exfoliated in thermoplastic polyurethane (TPU) matrix during melt-mixing. Wide angle X-ray diffraction, transmission electron microscopy and thermogravimetric analysis were used to investigate the microstructure of TPU nanocomposites. Three factors (including introducing sequence, the kind and the content of MAPP) showed important effects on the dispersion degree of OMMT-C18 in TPU matrix. The results confirmed that the pre-intercalation of MAPP was necessary for the exfoliation of OMMT-C18; however, the role of MAPP in TPU nanocomposites was different from that in polypropylene nanocomposites. In addition, the investigation on the morphology evolution of TPU nanocomposites showed that shear force played a key role in the formation of exfoliated TPU nanocomposites. TPU nanocomposites with exfoliated structure showed better properties compared with TPU and its nanocomposites with intercalated structure.     

Cellulose nanocrystal‐based poly(butylene adipate‐co‐terephthalate) nanocomposites covered with antimicrobial silver thin films

In this study, we reported the preparation and prospective application of the nanocomposites of poly(butylene adipate‐co‐terephthalate) (PBAT) reinforced with cellulose nanocrystals (CNCs). CNCs were isolated from bleached sugarcane bagasse by acid hydrolysis and functionalized with adipic acid. Nanocomposites were prepared with different concentration of CNCs (0.8, 1.5, and 2.3 wt% CNC) by solution‐casting method and then were covered with silver thin film by magnetron sputtering. The results showed that the surface modification increased the degree of crystallinity of nanocrystals from 51% to 56%, decreasing their length and diameter. Moreover, AFM‐IR spectroscopy revealed that the modified CNCs were covered by adipic acid molecules, improving the dispersion of nanocrystals in PBAT. Well‐dispersed modified CNCs acted as heterogeneous nuclei for crystallization of PBAT, and increased the storage modulus of the polymer by more than 200%. These improvements in thermal and mechanical properties of CNC‐based PBAT associated with the decrease of 56% in the Escherichia coli biofilm formation on nanocomposites (antibacterial properties) qualify the CNC/PBAT nanocomposites covered with silver thin films to be used as food packaging. POLYM. ENG. SCI., 59:E356–E365, 2019. © 2019 Society of Plastics Engineers     

Selective Laser Sintering 3D Printing: A Way to Construct 3D Electrically Conductive Segregated Network in Polymer Matrix

Selective laser sintering (SLS), which can directly turn 3D models into real objects, is employed to prepare the flexible thermoplastic polyurethane (TPU) conductor using self‐made carbon nanotubes (CNTs) wrapped TPU powders. The SLS printing, as a shear‐free and free‐flowing processing without compacting, provides a unique approach to construct conductive segregated networks of CNTs in the polymer matrix. The electrical conductivity for the SLS processed TPU/CNTs composite has a lower percolation threshold of 0.2 wt% and reaches ≈10⁻¹ S m⁻¹ at 1 wt% CNTs content, which is seven orders of magnitude higher than that of conventional injection‐molded TPU/CNTs composites at the same CNTs content. The 3D printed TPU/CNTs specimen can maintain good flexibility and durability, even after repeated bending for 1000 cycles, the electrical resistance can keep at a nearly constant value. The flexible conductive TPU/CNTs composite with complicated structures and shapes like porous piezoresistors can be easily obtained by this approach.     

Effect of modifiers on morphology and thermal properties of novel thermoplastic polyurethane‐peptized laponite nanocomposite

Laponite RDS (Laponite containing pyrophosphate based peptizer) was modified with cetyl trimethyl ammonium bromide (cLS) and dodecylamine hydrochloride (dLS), respectively. Thermoplastic polyurethane (TPU)‐modified Laponite RDS nanocomposites were prepared by solution mixing technique. Morphologies of these two modified clay‐nanocomposites are found to be markedly different. cLS based TPU nanocomposites exhibit partly exfoliated, intercalated, and aggregated structure at lower clay content but a network type of structure is observed at higher clay content. However, dLS based TPU nanocomposites demonstrate spherical cluster type of structure at all clay contents. Nearly two fold increase in storage modulus is observed in both glassy and rubbery state with merely 1% cLS content which gradually decreases with an increase in the clay content. However, in case of dLS filled nanocomposite, gradual increase in storage modulus is observed with an increase in the clay content. Thermogravimetric analysis (TGA) studies indicate that the temperature corresponding to 5 wt % degradation of TPU is enhanced by 19.1 and 12.5°C with the addition of merely 1% cLS and dLS, respectively. However, the activation energy of degradation of neat TPU, as determined by isothermal TGA analysis, is found to be higher than that of the nanocomposites containing 1% of cLS and dLS, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010