Mechanical Properties Of Polymer Nanocomposites Research Articles

Analyzing Tribological and Mechanical Properties of Polymer Nanocomposite for Brake Pad Applications - A Critical Review

A brake pad is an integral component of a vehicle's braking system, designed to impart controlled friction and, ultimately, assist in slowing or stopping a vehicle. Their constituents include binder, filler, abrasive, lubricant, and reinforcing fiber. Materials for brake pads must have excellent wear resistance, increased heat dissipation, a consistent coefficient of friction, low noise and vibration, durability, compatibility, minimal environmental impact, and cost-effectiveness. This paper aims to examine the various materials used in brake pad applications. They are composed of matrix, ceramic, and polymer composites, and are manufactured using various processes. In addition to mechanical and tribological testing, there are various methods for testing the mechanical and tribological properties of brake pads. Various instruments, such as SEM, TEM, AFM, and XRD, were surveyed in order to analyse the morphology and crystal structure of nanoscale brake pads. Various applications such as automobiles, railroads, and aerospace utilise brake pads. The study reveals that integrating nano-fillers into polymer composites significantly enhances the mechanical and tribological properties of automotive brake pads, offering a promising route toward more durable, efficient, and safer braking systems. Through this analysis, researchers will gain a deeper understanding of the materials used in brake pads and their adaptability for various applications.

Comprehensive 3-D homogenization approach for predicting mechanical properties and creep behavior of polymer nanocomposites reinforced with graphene nanoplatelets

The aim of this study is to provide a comprehensive 3-D homogenization approach based on the high-fidelity generalized method of cells method to predict the mechanical properties and creep behavior of polymer nanocomposite reinforced with graphene nanoplatelets. Several fundamental experimental aspects including the volume fraction, size, and random orientation of graphene nanoplatelets, the interphase region, and the aggregation state of nanofillers of graphene are taken into account. The present study introduces two novel perspectives. At first, the aggregation of graphene nanoplatelets is formulated as dependent on volume fraction. Then the size of graphene is formulated as an important factor affecting the interphase region and the mechanical properties of polymer nanocomposite. Micromechanical tests conducted using the proposed method illustrate the good agreement with experimental data. The results of the parametric study on different experimental aspects revealed important findings. (i) For a specific value of graphene nanoplatelet volume fraction, the mechanical properties of polymer nanocomposite are at the best state. By increasing the graphene content beyond the specified graphene content value, the effective properties of graphene are decreased. (ii) The size of graphene nanoplatelets and the characteristics of the graphene/polymer interphase region have a direct effect on the properties of the nanocomposite.

Effect of melt blending processing on mechanical properties of polymer nanocomposites: a review

Effect of melt blending processing on mechanical properties of polymer nanocomposites: a review

Investigating the Effect of Hydroxyl Functionalized MWCNT on the Mechanical Properties of PMMA-Based Polymer Nanocomposites

Aims: The aim of this study was to evaluate the mechanical properties of polymer nanocomposites (PNCs) reinforced with multiwalled carbon nanotubes (MWCNT). Methods: Mixing MWCNT into the polymer at very small propositions can enrich the mechanical properties of the polymer nanocomposites. Testing Specimen fabricated with 0.1wt%, 0.5wt%, 1wt% mixing ratios using extrusion and injection molding process. Computational analysis was performed through the square RVE model and analyzed with finite element analysis (FEA) using DIGIMAT simulation tool. The specimen was evaluated by ASTM D3039 for tensile strength and ASTM D7264 for flexural. Results: The simulated results were compared with experimental results. Scanning electron microscopy(SEM) was performed to evaluate the dispersion state of nanotubes in the matrix. Conclusion: The impactful improvement in mechanical properties is shown in the results after addition of functionalized MWCNTs (f-MWCNT) compared to pure polymer and non- functionalized MWCNT composites.

Insights into Uniaxial Tension and Relaxation of Nanorod-Filled Polymer Vitrimer Nanocomposites: A Molecular Dynamics Simulation

The mechanical properties of polymer nanocomposites (PNCs) depend sensitively on the structure (e.g., orientation, dispersion, and so on) of the incorporated nanofillers. Many studies have shown that the alignment of anisotropic nanofillers can improve the mechanical properties of PNCs. However, achieving this alignment typically requires complex preparation processes. To address this challenge, researchers have introduced dynamic covalent bonds to form reversible cross-linked polymer systems, which would lead to unique properties, such as self-healing, recyclability, and reprocessibility. In addition, inspired by the above ideas, we introduce nanorods as fillers into a linear vitrimer system to form nanorod vitrimer composites (NVCs). In NVCs, we can easily manipulate the alignment of the nanorods due to bond exchange reactions (BERs) in the vitrimer matrices. By using coarse-grained molecular dynamics (CGMD) simulations, we systematically investigate the factors affecting the nanorod orientation in NVCs. We find that the main factor affecting the nanorod orientation is the network rearrangement caused by BERs. Specifically, the BER potential barrier (ΔEsw) directly determines the probability of BERs’ occurrence. At the same time, the increase of the interfacial interaction between polymer chains and nanorods (εnp) confines the motion of the active beads, which slows down the rate of BERs. Additionally, the impact of temperature (T) and aspect ratio (ld) on the orientation of nanorods during uniaxial stretching or stress relaxation are also discussed. Finally, by combining uniaxial stretching and stress relaxation processes, we elucidate the orientation retention mechanism of NVCs and demonstrate the mechanical property enhancement phenomenon of the pre-oriented NVC systems. This work provides a simple strategy for manipulating the nanorod alignment in vitrimer matrices and uncovers guidelines for designing new functional polymer vitrimer nanocomposites at the molecular level.

Cellulose nanocrystal functionalized aramid nanofiber reinforced epoxy nanocomposites with high strength and toughness

The mechanical properties of polymer nanocomposites can be improved by incorporating various types of nanofillers. The hybridization of nanofillers through covalent linkages between nanofillers with different dimensions and morphology can further increase the properties of nanocomposites. In this work, aramid nanofibers (ANFs) are modified using chlorinated cellulose nanocrystals (CNCs) and functionalized with 3-glycidoxypropyltrimethoxysilane to improve the chemical and mechanical interaction in an epoxy matrix. The integration of CNC functionalized ANFs (fACs) in the epoxy matrix simultaneously improves Young’s modulus, tensile strength, fracture properties, and viscoelastic properties. The test results show that 1.5 wt% fAC reinforced epoxy nanocomposites improve Young’s modulus and tensile strength by 15.1% and 10.1%, respectively, and also exhibit 2.5 times higher fracture toughness compared to the reference epoxy resin. Moreover, the glass transition temperature and storage modulus are found to increase when fACs are incorporated. Thus, this study demonstrates that the enhanced chemical and mechanical interaction by the CNC functionalization on the ANFs can further improve the static and dynamic mechanical properties of polymer nanocomposites.

Formation of nanoparticle aggregates and agglomerates in polymer nanocomposites and their distinct impacts on the mechanical properties

AbstractIn this study, the different effects of nanoparticle aggregates and agglomerates on the mechanical properties of polymer nanocomposites are comprehensively investigated. To this end, a specific strategy, based on the equilibrium between the dispersion and cohesion energies in the mixing stage, is proposed using which the content and size of aggregates/agglomerates can be defined. The aggregated/agglomerated networks are considered to place in constrained volumes (CVs), having co‐continuous morphology. An equivalent box model (EBM), corresponding to the system, is used to predict the tensile modulus of the nanocomposite. Different test results of HDPE nanocomposite samples, containing 1–3 wt.% of surface‐modified silica nanoparticles, prepared by a semi‐industrial single screw extruder, are applied to validate the model. Moreover, other data from the literature are also used to further evaluate the accuracy and capability of the proposed analytical method.

Influence of Reinforcing Efficiency of Clay on the Mechanical Properties of Poly(butylene terephthalate) Nanocomposite

In contrast to traditional fillers, clay, in particular, natural smectite clay, represents an environmentally significant alternative to improve the properties of polymers. Compared to conventional nanofillers, smectite clay can effectively enhance the physical and mechanical properties of polymer nanocomposites with a relatively small amount of addition (<5 wt%). The present study focuses on investigating the reinforcing efficiency of different amounts (up to 5 wt%) of a natural Brazilian smectite clay modified (MBClay) on the mechanical properties of poly(butylene terephthalate) (PBT) nanocomposites and also evaluates the correlation between MBClay addition and the mechanical and thermal behaviors of the PBT/MBClay nanocomposites. Natural Brazilian clay modified by the addition of quaternary salt and sodium carbonate (MBClay) was infused into the PBT polymer by melt extrusion using a twin-screw extruder. It was found that the best properties for PBT were obtained at 3.7 wt% of modified BClay. Tensile strength at break exhibited increased by about 60%, flexural strength increased by 24%, and flexural modulus increased by 17%. In addition, an increase in the crystallinity percentage of PBT/BClay nanocomposite was confirmed by DSC and XRD analysis, and a gain of about 45% in HDT was successfully achieved due to the incorporation of 3.7 wt% of MBClay.

Multi-factor analysis of the effects of graphene oxide nanoplatelets on self-healing polymer composites based on micromechanical FE simulation

To investigate the effects of graphene oxide (GO) nanoplatelets and mixed self-healing microcapsules on the mechanical properties of polymer nanocomposites, a multi-factor analysis was made based on numerical experimental results, which comprehensively reveals the influences of structural parameters (including the volume fraction, aspect ratio, orientation of GO and the content of self-healing microcapsules). A series of micromechanical FE models of nanocomposites containing randomly-distributed nanoplatelets were established and validated by experimental data. The competing failure mechanisms of matrix damage and interface debonding have been fully considered in the simulation. The significance levels of the nanocomposite’s structural parameters were quantitatively determined finally, and it was found that the volume fraction is the most significant factor and the aspect ratio is the next (the weights are 46.1% and 21.7%, respectively). The work would provide effective theoretical instructions in the material design and optimization of GO-reinforced self-healing polymer nanocomposites.

Melt State Reinforcement of Polyisoprene by Silica Nanoparticles Grafted with Polyisoprene.

We systematically vary the nanoparticle (NP) dispersion state in composites formed by mixing polyisoprene homopolymers with polyisoprene grafted silica particles, and demonstrate how creep measurements allow us to overcome the limitations of small amplitude oscillatory shear (SAOS) experiments. This allows us to access nearly 13 orders in time in the mechanical response of the resulting composites. We find that a specific NP morphology, a percolating particle network achieved at intermediate graft densities, significantly reinforces the system and has a lower NP percolation loading threshold relative to other morphologies. These important effects of morphology only become apparent when we combine creep measurements with SAOS re-emphasizing the role of synergistically combining methods to access the mechanical properties of polymer nanocomposites over broad frequency ranges.

Mechanical properties of polymer nanocomposites with randomly dispersed and cross-linked two-dimensional diamond

Polymer nanocomposites with excellent mechanical performances have been increasingly sought after in engineering applications such as biotechnology, aerospace, and automotive areas. Through molecular dynamics (MD) simulation, this work systematically assessed the tensile performance of poly(methyl methacrylate) (PMMA) nanocomposite reinforced by randomly dispersed two-dimensional diamond-diamane. It is found that randomly dispersed diamane effectively enhances the tensile properties of PMMA with surface functionalization, and the enhancement effect can be remarkably augmented by cross-linking. Simulations reveal that the enhancement effect can be effectively tailored by the alignment of the diamane fillers. The PMMA nanocomposites exhibit much better tensile performance when the diamane fillers are uniformly aligned along the in-plane direction of the filler. Additional investigations show that larger diamane filler is preferred without cross-linking, while smaller diamane filler should be considered when cross-linking is present. Overall, the impacts of different factors on the tensile properties of PMMA nanocomposites are analysed in-depth in this work, which provides atomistic insights for the preparation of polymer nanocomposites with desired mechanical properties.

Atomic insights into synergistic effect of pillared graphene by carbon nanotube on the mechanical properties of polymer nanocomposites

Molecular dynamics simulations have been performed to explore the underlying synergistic mechanism of pillared graphene or non-covalent connected graphene and carbon nanotubes (CNTs) on the mechanical properties of polyethylene (PE) nanocomposites. By constructing the pillared graphene model and CNTs/graphene model, the effect of the structure, arrangement and dispersion of hybrid fillers on the tensile mechanical properties of PE nanocomposites was studied. The results show that the pillared graphene/PE nanocomposites exhibit higher Young’s modulus, tensile strength and elongation at break than non-covalent connected CNTs/graphene/PE nanocomposites. The pull-out simulations show that pillared graphene by CNTs has both large interfacial load and long displacement due to the mixed modes of shear separation and normal separation. Additionally, pillared graphene can not only inhibit agglomeration but also form a compact effective thickness (stiff layer), consistent with the adsorption behavior and improved interfacial energy between pillared graphene and PE matrix.

Versatilely Manipulating the Mechanical Properties of Polymer Nanocomposites by Incorporating Porous Fillers: A Molecular Dynamics Simulation Study.

Polymer nanocomposites (PNCs) have been attracting myriad scientific and technological attention due to their promising mechanical and functional properties. However, there remains a need for an efficient method that can further strengthen the mechanical performance of PNCs. Here, we propose a strategy to design and fabricate novel PNCs by incorporating porous fillers (PFs) such as metal-organic frameworks with ultrahigh specific surface areas and tunable nanospaces to polymer matrices via coarse-grained molecular dynamics simulations. Three important parameters─the polymer chain stiffness (k), the interaction strength between the PF center and the end functional groups of polymer chains (εcenterend), and the PF weight fraction (w)─are systematically examined. First, attributed to the penetration of polymer chains into PFs at a strong εcenterend, the dimension of polymer chains such as the radius of gyration and the end-to-end distance increases greatly as a function of k compared to the case of the neat polymer system. The penetration of polymer chains is validated by characterizing the radial distribution function between end functional groups and filler centers, as well as the visualization of the snapshots. Also, the dispersion state of PFs tends to be good because of the chain penetration. Then, the glass transition temperature ratio of PNCs to that of the neat systems exhibits a maximum in the case of k = 5ε, indicating that the strongest interlocking between polymer chains and PFs occurs at intermediate chain stiffness. The polymer chain dynamics of PNCs decreases to a plateau at k = 5ε and then becomes stable, and the relative mobility to that of the neat system as well presents the same variation trend. Furthermore, the mechanical property under uniaxial deformation is thoroughly studied, and intermediates k, εcenterend, and w can bring about the best mechanical property. This is because of the robust penetration and interaction, which is confirmed by calculating the stress of every component of PNCs with and without end functional groups and PF centers as well as the nonbonded interaction energy change between different components. Finally, the optimal condition (k = 5.36ε, εcenterend = 5.29ε, and w = 6.54%) to design the PNC with superior mechanical behavior is predicted by Gaussian process regression, an active machine learning (ML) method. Overall, incorporating PFs greatly enhances the entanglements and interactions between polymer chains and nanofillers and brings effective mechanical reinforcements with lower filler weight fractions. We anticipate that this will provide new routes to the design of mechanically reinforced PNCs.

Molecular Dynamics Simulations of Polymer Nanocomposites Welding: Interfacial Structure, Dynamics and Strength.

Polymer welding has received numerous scientific attention, however, the welding of polymer nanocomposites (PNCs) has not been studied yet. In this work, via coarse-grained molecular dynamics simulation, the attention on investigating the welding interfacial structure, dynamics, and strength by constructing the upper and lower layers of PNCs, by varying the polymer-nanoparticle (NP) interaction strength εNP-p is focused. Remarkably, at low εNP-p , the NPs gradually migrate into the top and bottom surface layer perpendicular to the z direction during the adhesion process, while they are distributed in the middle region at high εNP-p . Meanwhile, the dimension of polymer chains is found to exhibit a remarkable anisotropy evidenced by the root-mean-square radius of gyration in the xy- (Rg,xy ) and z- (Rg,z ) component. The welding interdiffusion depth increases the fastest at low εNP-p , attributed to the high mobility of polymer chains and NPs. Lastly, although the mechanical properties of PNCs at high εNP-p is the strongest because of the presence of the NPs in the bulk region, the welding efficiency is the greatest at low εNP-p . Generally, this work provides a fundamental understanding of the interfacial welding of PNCs, in hopes of guiding to design and fabricate excellent self-healable PNCs.

Effect of nanoparticle size on the mechanical properties of polymer nanocomposites

The mechanical properties of a series of polymer nanocomposites (PNCs) of polyvinylacetate (PVAc) and carbon dots (CDs) with average diameters of 2.5 and 8.5 nm (denoted as CD-2.5 and CD-8.5, respectively) or carbon black (N330) were investigated. The results show that when the nanoparticle size larger than the tube diameter of PVAc, e.g. N330 and CD-8.5, the complex viscosity, reptation relaxation time, and elongation at break of the PNCs get larger with decrease of particle size whereas the tensile stress becomes smaller. For CD-2.5 with size comparable to the Kuhn segment length, the well-dispersed CD-2.5 induces the decrease of complex viscosity and reptation relaxation time, and thus results in an intermediate tensile stress and reduced elongation at break. The possible origins of the different reinforce mechanism were explained and it is inferred that whether the existence of a critical size of the nanoparticles for an effective reinforcement is still needed to be explored.

Effect of agglomeration and dispersion on the elastic properties of polymer nanocomposites: A Monte Carlo finite element analysis

Abstract Owing to their superior mechanical and physical properties, carbon nanotubes (CNT) seem to hold a great promise as an ideal reinforcing material for composites of high-strength and low-density. In most of the experimental results up to date, however, only modest improvements in the strength and stiffness have been achieved by incorporating carbon nanotubes in polymers. In the present paper, the influence of single wall carbon nanotube agglomeration on the effective stiffness is analyzed by using an Eshelby’s inclusion model. Analytical expressions are derived for the effective elastic stiffness of single wall carbon nanotubereinforced composites with the effects of agglomeration. The present study not only provides the important relationship between the effective properties and the morphology of CNT-reinforced composites, but also may be useful for improving and tailoring their mechanical properties. In addition, a multiscale Monte Carlo finite element method (MCFEM) was used for determining mechanical properties of polymer nanocomposites (PNC) that consist of polymers reinforced with single-walled carbon nanotubes (SWCNT). Specifically, the method uses a multiscale homogenization approach to link the structural variability at the nano/micro scales with the local constitutive behavior. Subsequently, the method incorporates a FE scheme to determine the Young’s modulus and Poisson ratio of PNC. The use of the computed properties in macroscale modeling is validated by comparison with experimental tensile test data.

Study of the nanostructure and the local mechanical properties of polypropylene multifunctional materials

Polymer-based multifunctional materials reinforced with graphene represent a step forward due to the combination of good structural properties with others of different nature such us electrical conductivity. These new systems are good candidates for applications in the transportation industry provided that the nanofiller is well-dispersed within the matrix and there is a good interaction between the fibre and the polymer. The aim of this work is the study of the nanostructure and the mechanical properties of polymer nanocomposites based on polypropylene (PP) and graphene with concentrations in the range of 0.9 to 2.6 vol.%. The nanostructure of the composites was investigated by wide angle x-ray scattering and the local mechanical properties were assessed by nanoindentation. On the one hand, nanoindentation studies revealed a good distribution of the nanofiller within the polymer matrix. On the other hand, an enhancement of the mechanical properties by the incorporation of graphene was found. This mechanical improvement was attributed to the intrinsic properties of graphene while there were no clear differences in the nanostructure of the nanocomposites compared to that of neat PP. Finally, comparison of the moduli from nanoindentation and tensile testing allowed the understanding of the mechanism of deformation of these materials under external stresses of different nature.

A methodology for determining the local mechanical properties of model atomistic glassy polymeric nanostructured materials

We propose a methodology for calculating the distribution of the mechanical properties in model atomistic polymer-based nanostructured systems. The use of atomistic simulations is key in unravelling the fundamental mechanical behavior of composite materials. Most simulations involving the mechanical properties of polymer nanocomposites (PNCs) concern their global (average) properties, which are typically extracted by applying macroscopic strain on the boundaries of the simulation box and calculating the total (global) stress by invoking the Virial formalism over all atoms within the simulation box; thus, extracting the pertinent mechanical properties from the corresponding stress-strain relation.However, in order to probe the distribution of mechanical properties within heterogeneous multi-component polymer-based systems, a detailed computation of stress and strain fields within specific sub-domains is necessary. For example, it is well known for multi-component nanostructured systems, such as PNCs, that the mechanical behavior of the polymer/nanofiller interphases, or interfaces, is crucial for determining the global mechanical properties of the composite materials. Here we propose a new methodology to probe the distribution of mechanical properties by directly computing the (local) stress and strain at the atomic level, and averaging over user-defined subdomains. The workflow of our computational method possesses the following features:•Calculating the stress and strain per atom (or per particle) for nanostructured microscopic (here atomistic) model configurations, under an imposed applied deformation.•Averaging the local, per-atom defined, stress and strain on user-defined subdomains within the nanostructured model system.•Predicting the mechanical properties within the specific subdomains, focusing on polymer/solid interphases.

Enhanced mechanical and dynamic mechanical properties of polymer nanocomposites containing carbon nanotubes decorated with barium titanate

This study presents functionalized carbon nanotubes (CNTs) decorated with functionalized barium titanate (BT) (denoted as BT@CNTs) via hydrothermal and self-assembly methods to improve dispersion in polypropylene (PP) matrix with enhanced thermal, mechanical, and thermomechanical properties. The CNTs, BT, and BT@CNTs with the addition of polypropylene maleic anhydride (PPMA) compatibilizer were used in the fabrication of the PP based nanocomposites for this study via solution mixing and melt compounding. FTIR, TEM, and SEM analyses, respectively revealed that the nanoparticles were successfully functionalized, CNTs decorated with BT, and well dispersion in the PP matrix. PP/BT@CNTs-based nanocomposite showed optimal tensile strength, modulus, heat deflection, and thermal stability of about 16.8%, 26.5%, 20.1%, and 30oC higher than that obtained for the pure PP. These properties were also respectively 10.6%, 17.6%, 19.0%, and 5.0oC higher than PP/3CNTs nanocomposite when compared to PP/3BT@CNTs. The PP/BT@CNTs based nanocomposites also revealed enhanced dynamic mechanical properties. The better performance in the measured properties of PP/BT@CNTs compared to pure PP and PP/CNTs were attributed to their uniform microstructures, effective interlocking of the PP matrix due to the presence of BT on CNTs surfaces.

Pore-Confined Polymers Enhance the Thermal Conductivity of Polymer Nanocomposites.

Molecularly confined polymer fillers in nanopores were found to give superior mechanical properties of polymer nanocomposites. In this work, we study the thermal conductivity of such nanocomposites and unveil the effect of polymer confinement on thermal conductivity. Using the time-domain thermoreflectance method, we measure the cross-plane thermal conductivity of polymer nanocomposites that consist of polystyrene fillers confined within a nanoporous organosilicate matrix. Compared to unconfined bulk polystyrene fillers, we find that pore-confined polystyrene fillers enhance the thermal conductivity of the polymer nanocomposites. This enhancement is attributed to the better aligned and less entangled chains in the confined phase, where chain-chain phonon scatterings are reduced. Our work provides essential insights into the thermal conductivity of polymer nanocomposites for multifunctional thermal and mechanical applications.