Influence of fused filament fabrication parameters on tensile properties of polylactide/layered silicate nanocomposite using response surface methodology

This study aimed at assessing and optimizing the influence of printing speed and extrusion temperature in a fused filament fabrication (FFF) process on the tensile properties of a polylactide/layered silicate nanocomposite. Mathematical models using Doehlert designs were formulated to examine factor and interaction effects. The models were corroborated by measurements using capillary rheology, tomographic images, and crystallinity analyses to find physical explanations for the differences in tensile properties. The tensile properties were a non-monotonic function of printing speed, which may be due to various deposition defects that influence the porosity of composite tensile specimens. This study provides new insights into FFF process optimization regarding rheological behavior and mesostructure of nanocomposite by highlighting new modes of deposition defects that originate from process parameter settings and materials. The results contribute to the properties mastery of FFF-processed materials.     

Insights into the synergistic mechanism of reactive aliphatic soft chains and nano-silica on toughening epoxy resins with improved mechanical properties and low viscosity

Toughening epoxy resin (EP) without sacrificing strength, modulus, and processing performance is always a harsh task. Here, a series of epoxy systems containing soft butyl glycidyl ether (BGE) and rigid nano-silica (nano-SiO₂) were prepared. Micro-phase separation structures derived from the self-assembly effect of BGE can be observed in atomic force microscopy images by controlling the total amount of BGE and nano-SiO₂ at 2 wt% for the EP_C:Si-m:n (m + n = 4) systems. Due to the synergistic effect of self-assembly effect of BGE and the rigid effect of well dispersed nano-SiO₂, EP_C:Si-2:2 system exhibited improvement of tensile strength of 59.3% (92.63 MPa), tensile modulus of 24.8% (3.52 GPa), elongation at break of 78.6% (4.84%), and glass transition temperature of 2.4% (138.4°C) compared with Pure EP system. Besides, due to the low loading of nano-SiO₂ (≤2 wt%) and the dilution effect of BGE, the viscosity of all the toughening systems is lower than 600 mPa·s, which can provide this toughening system with superior processing performance for large production of composites by automotive manufacturing methods such as vacuum assistant resin infusion technology.     

Effects of carbon fillers on tensile and flexural properties in polypropylene‐based resins

A potential application for conductive resins is in bipolar plates for use in fuel cells. The addition of carbon filler can increase the electrical and thermal conductivities of the polymer matrix but will also have an effect on the tensile and flexural properties, important for bipolar plates. In this research, three different types of carbon (carbon black, synthetic graphite, and carbon nanotubes) were added to polypropylene and the effects of these single fillers on the flexural and tensile properties were measured. All three carbon fillers caused an increase in the tensile and flexural modulus of the composite. The ultimate tensile and flexural strengths decreased with the addition of carbon black and synthetic graphite, but increased for carbon nanotubes/polypropylene composites due to the difference in the aspect ratio of this filler compared to carbon black and synthetic graphite. Finally, it was found that the Nielsen model gave the best prediction of the tensile modulus for the polypropylene based composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of resin modifiers on the structural properties of epoxy resins

Thermomechanical, mechanical and fracture mechanical properties of modified epoxy resins with two different modifiers are investigated. Carboxyl‐terminated butadiene‐acrylonitrile (CTBN) is used as toughening agent and hexanediole diglycidyl ether (HDDGE) as reactive diluent. Both modifiers are admixed in contents from 0 up to 100 phr (parts per hundred resin) and exhibit flexibilizing and toughening qualities. The glass transition temperature is strongly depressed by the admixed reactive diluent, whereas the tensile modulus exhibits greater dependency on the toughening agent contents. The tensile strength and strain at break values are higher for the formulations with diluent compared to resins with toughening agent. Up to a content of 45 phr both modified systems exhibit comparable fracture toughness values. Only the toughened systems comprise increasing values for modifier amounts higher than 45 phr. For the formulation with both modifiers (toughening agent and diluent) a significantly higher toughness but a reduced glass transition temperature was obtained. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45348.     

Amine/epoxy stoichiometric ratio dependence of crosslinked structure and ductility in amine-cured epoxy thermosetting resins

Epoxy-amine thermosetting resins undergo different reactions depending on the amine/epoxy stoichiometric ratio (r). Although many desirable properties can be achieved by varying the stoichiometric ratio, the effects of the variation on the crosslinked structure and mechanical properties and the contribution of these factors to the ductility of materials have not been fully elucidated. This study investigates the brittle-ductile behavior of epoxies with various stoichiometric ratios and performs curing simulations using molecular dynamics (MD) to evaluate the crosslinked structures. The molecular structure is predominantly branched in low-stoichiometric ratio samples, whereas the chain extension type structure dominates the high-stoichiometric ratio samples. As a result, the higher-stoichiometric ratio samples enhances the ductility of materials and the elongation at break increases form 1.4% (r = 0.6) to 11.4% (r = 1.4). Additionally, the tensile strength (105.4 MPa) and strain energy (7.96 J/cm³) are maximum at r = 0.8 and 1.2, respectively. On the other hand, the Young's modulus is negatively impacted and it decreased from 4.2 to 2.7 GPa with increasing stoichiometric ratio.     

How the biaxially stretching mode influence dielectric and energy storage properties of polypropylene films

The most important polymer film used in commercial capacitors is biaxially oriented polypropylene (BOPP), which could be produced by sequentially or simultaneously biaxial orientation after the melt-extrusion. In order to disclose the influence of the stretching technique on the properties of films, the BOPP films with varied thickness were fabricated by sequential and simultaneous orientation, respectively. Compared to the sequentially biaxially stretched films, the crystal grains in the simultaneously biaxially stretched films are more isotropically dispersed. As temperature increases, all the BOPP films exhibit similar dielectric constant, and the simultaneous films have much lower dielectric loss thanks to the finer blended crystalline and amorphous phases. When the film thickness is smaller than 5 μm, the breakdown field strength, energy density and discharging time of the simultaneous films can be increased by at least 10% comparing to the sequential ones, which is very important for reducing the volume of the film capacitors. All the results suggest the simultaneously biaxial orientation mode shows significant advantages in producing thin BOPP films with better mechanical and electrical properties.     

Measure of polymer performance based on correlated physical parameters

We introduce a novel measure of performance of polymer composites based on physical parameters whose behavior depends on levels of dopant concentration used during their preparation. The performance measure is based on a joint analysis of measurements of the physical parameters exhibiting non-trivial correlations that vary across different levels of dopant concentrations. In contrast to traditional multivariate analysis, we treat data from parameter measurements as being obtained from functional parameters, and develop the performance measure based on the joint average function of parameters that encodes the correlation structure. An optimal level of dopant concentration is then ascertained with respect to the performance measure. While the proposed measure is general enough to be applicable to any chosen physical parameters, we demonstrate its utility in the context of assessing performance using microstructural and nonlinear optical parameters. Computing of the measure and optimal dopant concentration are carried out using Monte Carlo sampling, which further facilitates uncertainty quantification.     

Effect of temperature on tensile and creep-recovery properties of braided polyester harness cord

Tensile and creep-recovery properties of braided polyester (PET) harness cord under various temperature and tension were studied by using an Instron universal tester. The study reveals that the tensile properties are highly related to the temperature, with a decrease of 29.6, 50.0, and 33.8% in initial modulus, yield force, and breaking force (BF), respectively, as increasing the temperature from 25 to 100 °C. Under the condition of 5% BF, the creep and recovery strain of harness cord increased by 185.7 and 353.8% separately, when the temperature increased from 40 to 100 °C, indicating the significant effect of temperature and tension on the creep-recovery properties. The similar tendencies were also observed under the conditions of 10 and 15% BF. These results could be well described by Burgers four-element model. During the 1.5 h creep test, only instant elastic and retarded elastic deformation could be observed and accounting for 56.1–84.3% and 15.2–43.4% of the total creep deformation, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47864.     

Effect of the wine lees wastes as cost-advantage and natural fillers on the thermal and mechanical properties of poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBH) and poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV)

Solid wine wastes named wine lees (WL) have been tested as cost-advantage filler within biopolymers such as poly(3-hydroxybutyrate-co-hydroxyhexanoate) and poly(3-hydroxybutyrate-co-hydroxyvalerate). WL have been first characterized and subsequently mixed within the polymers through a twin-screw extruder in different concentrations (10, 20, and 40 phr). Moreover, the role of 3-methacryloxypropyltrimethoxysilane tested as coupling agent has been investigated within the 20 phr formulation. The obtained materials have been characterized from a thermal, mechanical, rheological, and morphological point of view through: differential scanning calorimetry, melt flow rate, tensile and creep tests, dynamic mechanical analysis, and scanning electron microscopy. Results have shown how WL can improve the biopolymers overall properties without compromising their bio-based origin. Several micromechanical models have been exploited to extend the mechanical behavior and correlations between biocomposites properties and WL contents have been carried out. Finally, the economic analysis has shown how these biocomposites could be suitable also for large-scale applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48869.     

Correlating the 3D melt electrospun polycaprolactone fiber diameter and process parameters using neural networks

In the present work, we developed an artificial neural networks (ANN) model to predict and analyze the polycaprolactone fiber diameter as a function of 3D melt electrospinning process parameters. A total of 35 datasets having various combinations of electrospinning writing process variables (collector speed, tip to nozzle distance, applied pressure, and voltage) and resultant fiber diameter were considered for model development. The designed stand-alone ANN software extracts relationships between the process variables and fiber diameter in a 3D melt electrospinning system. The developed model could predict the fiber diameter with reasonable accuracy for both train (28) and test (7) datasets. The relative index of importance revealed the significance of process variables on the fiber diameter. Virtual melt spinning system with the mean values of the process variables identifies the quantitative relationship between the fiber diameter and process variables.     

Deeper insights into the thermal properties of epoxy thermoset resins using torsion measurements

The glass transition temperature (T_g) of epoxy thermosets is a critical material property that depends on the component chemistry, the final cross-link density, and processing conditions. This study incorporates dynamic mechanical analysis (DMA) testing with a torsion clamp geometry on a TA Instruments DHR-2 and differential scanning calorimetry (DSC) to characterize five different two-component epoxy-amine systems. Investigation of the T_g dependence on DMA frequency and heating shows that lowering the frequency from 1 to 0.01 Hz results in a T_g very similar to that measured using DSC, while a heating rate of 0.3°C/min using DMA gives a T_g comparable to the DSC measured value at 30°C/min. The DMA technique reveals secondary relaxation transitions and peak broadening in the tan(δ) plots of poorly mixed epoxy blends, quantified using full width at half maximum (FWHM) of tan(δ) peaks, and are indicative of a non-homogeneous cross-linked network and off-ratio blending, respectively. The increase in the FWHM due to poor mixing ranges from 8% to 96%. These parameters are easily measurable and quantifiable in DMA, but are not observed in DSC. The additional DMA insights are valuable for process development and failure analysis, and can improve the understanding of epoxies.     

Effects of nanoparticle size and concentration on optical,toughness, and thermal properties of polycarbonate

The influences of size and content of silicon dioxide (SiO₂) nanoparticles on the morphological, optical, toughness, and thermal properties of polycarbonate (PC) were investigated. The PC nanocomposites were prepared using a twin-screw extruder followed by injection molding. The scanning electron microscope (SEM) micrographs displayed an adequate level of nano-SiO₂ particle distribution within the PC matrix but still revealed some agglomerated particles. Upon increasing the content of nanoparticles, slightly larger agglomerates formed. These agglomerated particles caused a reduction in material transparency due to light loss via reflection and scattering. However, the incorporation of nano-SiO₂ into the PC matrix greatly improved toughness properties and slightly increased glass-transition temperature (T_g), in conjunction with filler content (up to 4 vol %). This was particularly in the case with the smaller sized nano-SiO₂, which not only significantly improved toughness but also enhanced optical properties of the PC nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47634.     

Internal stress analysis of epoxy adhesively-boned joints based on their thermomechanical properties at cryogenic temperature

Internal stress analysis is essential to structural design of materials applied in cryogenic engineering. In this contribution, thermomechanical properties including dynamic thermomechanical properties and thermal expansion behavior of four epoxy resins, namely the polyurethane modified epoxy resin (PUE), diglycidyl ether of bisphenol A (DGEBA), tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) and triglycidyl-p-aminophenol (TGPAP) were studied by dynamic thermomechanical analysis. Internal stress of the epoxy layer in the bonded joint was calculated based on the thermomechanical properties. Meanwhile, the structure-cryogenic property relationship of epoxy resins were investigated. Results demonstrate that internal stress in the four epoxies bonded joints is 6 ~ 21 MPa at −150°C, and is positively correlated with the average thermal expansion coefficient (CTE) of epoxy resins. TGDDM and TGPAP showed higher retention of lap shear strength both at −196°C and after temperature cycling due to their lower CTE. Morphology of the fractured surface of bonded joints demonstrated that internal stress is responsible for the severe interface failure at −196°C. It reveals that selection of epoxy resins with low CTE is beneficial for designing high-performance epoxy adhesive systems served at cryogenic temperature.     

Effect of nano fillers on the properties of polytetrafluoroethylene composites: Experimental and theoretical simulations

Polytetrafluoroethylene (PTFE) has excellent corrosion resistance and a low coefficient of friction; however, its high wear rate and low hardness severely limit its use. In the work, nano particles were used as fillers for PTFE. The composites were prepared by the homogeneous mixing of PTFE and other fillers and sintered at high temperatures. The work aimed to investigate the effect of various nano fillers (nanocarbon powders, graphene, fullerene, nano graphite powders, and nano copper powders) on the mechanical, thermal, and frictional properties of composites. The results of the experiments showed that the addition of graphene could improve the stress and strain values of the composites, and all the nano fillers could improve the thermal conductivity of the PTFE composites. The friction experiments showed that fullerenes could significantly improve the wear resistance of PTFE composites. In the theoretical simulation, the thermal conductivity of PTFE composites was predicted using ANSYS software, with the changes in the temperature and friction force in the friction process. The theoretical simulation results matched with the experimental values, which proved the accuracy of the theoretical simulations.     

Effect of nanosilica with different interfacial structures on mechanical properties of polyimide/SiO2 composites

In this article, the effects of coupling agent, silica particle size, and particle shape on the mechanical properties of polyimide (PI) were studied by molecular dynamics (MD) simulations, and the effect of SiO₂ surface treated with coupling agent on the mechanical properties of PI was investigated by experiment. At the same doping volume fraction (5%), the simulation results show that the surface interaction energy between the matrix and particle gradually increases with the radius of the embedded nanoparticles. Meanwhile, the interface interaction energy and mechanical properties of the sphere-type were significantly higher than the ones of other shaped nanoparticles. Moreover, the simulations were compared with the experimental results; atomic force microscopy and scanning electron microscopy images can verify that after being treated with coupling agent, interface interaction between nanosilica and PI enhances quite a little. The mechanical experimental results show that the tensile strength and elasticity modulus of pure PI, unbonded (UB) PI/SiO₂, and bonded PI/SiO₂ films are 34.47 and 1.13, 36.46 and 1.32, and 66.20 MPa and 1.72 GPa, respectively. It is indicated that the coupling agent plays a crucial role in nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48595.     

Evaluation of mechanical properties and hydrophobicity of room-temperature,moisture-curable polysilazane coatings

Polysilazane coatings have a broad need in real-life applications, which require low processing or working temperature. In this work, five commercially available polysilazanes have been spin-coated on polycarbonate substrates and cured in ambient environment and temperature to obtain transparent, crack-free, and dense films. The degree of crosslinking is found to have a significant impact on the hardness and Young's modulus of the polysilazane films but has a minor influence on the film thickness and hydrophobicity. Among all five polysilazane coatings, the inorganic perhydropolysilazane-based coating exhibits the largest hardness (2.05 ± 0.01 GPa) and Young's modulus (10.76 ± 0.03 GPa) after 7 days of curing, while the polyorganosilazane-derived films exhibit higher hydrophobicity. The molecular structure of polysilazanes plays a key role in mechanical properties and hydrophobicity of the associated films, as well as the adhesion of coatings to substrates, providing an intuitive and reliable way for selecting a suitable polysilazane coating material for a specific application.     

Tensile deformation and morphology changes in segmented elastomer films and fibers including mechanical property modeling

Segmented polyether soft segment (SS) elastomers with different hard segments (HS) in film and fiber form were studied by birefringence, DSC, and tensile tests. To understand the morphological contributions to property differences, high resolution tapping AFM resolved ribbon-like highly anisotropic hard domain (HD) lamellae in low modulus Pebax (polyamide 12 HS) and polyetherester (PEE), films, while lower HS content high melting poly(urethane urea) (PUU) had much smaller less anisotropic but higher melting HDs, explaining its enhanced thermal and mechanical hysteresis properties. Stress–strain tensile data demonstrate the excellent strength and toughness of PUUs and some spun PEE fibers, and film and fiber birefringence data applied during strain cycling up to very high stresses provided the molecular basis for the varying properties. The parameters from non-Gaussian fits of tensile data provide insight into network properties for these systems exhibiting very high strengths and a large degree of strain hardening. Modeling of PEE and Pebax films also shows the effects of substantial plastic yielding of the HD networks. Tensile data were obtained as a function of strain rate and temperature to help understand the contributions of network restructuring and other factors. For fibers, strain rate data spanning seven decades show and unusual drop in strengths at very high strain rates. Temperature-dependent tensile data also show large differences between PUU materials versus lower melting PEEs.     

Surface energy evaluation of casting and nanofiber polyurethane films by using different models

The components of the surface free energy (SFE) were determined from static contact angle measurements of five liquids using different methods. The two manufacturing techniques (casting and electrospinning) applied to obtain polyurethane (PU) membranes give surfaces with different wetting properties. The SFE data varied and were strongly dependent on calculations methods and liquids that were used for contact angle measurements. As a whole, the SFE of electrospun PU membrane (PU-N) (~24 mN/m) was slightly higher than that of casting PU membrane (PU-F) (~18 mN/m) with similar chemical compositions. The overall increase in the value of SFE is mainly due to the microstructures with increased surface area and modulations of nanofibers. The results evidence the impact of the PU membrane preparation on the properties of the biomaterial surface. Such structure–properties–function relationship is necessary to lay the groundwork for establishing a set of design criteria to guide the fabrication of synthetic materials.     

Hybrid mathematical modeling and multi-objective optimization of mechanical properties of green composites based on starch and modified rice straw fillers

A hybrid mathematical modeling/optimization approach based on the response surface methodology (RSM) and desirability function (DF) capabilities was applied here to imitate and optimize the mechanical properties of thermoplastic starch-based biocomposites. In order to prepare the biodegradable and renewable biocomposites, rice straw (RS) was chemically modified to obtain more effective sustainable reinforcing fillers for starch, having semi-thermoset and core-shell structures. A combination of different RS products was used in the biocomposites and the composition of RS-based fillers was chosen as control variable. A series of experiments, by using RSM, were designed to assess the effects of filler loading and composition on the Young modulus, tensile strength, ultimate strain, and absorbed energy of the biocomposites. The best-fitting regression functions were identified via RSM statistical analysis and transformed into DF to optimize the desired responses concurrently. The findings demonstrate that the starch/RS product biocomposites with optimum elastic modulus (339.3 MPa), tensile strength (9.8 MPa), elongation at break (13.8%), and absorbed energy (1831.2 kJ/m²) were obtained by incorporating RS-based fillers with both semi-thermoset and core-shell structures in combination with each other at loadings of 13.5 and 6.5 phr, respectively.