https://cyberleninka.org/article/n/1018032.pdf

Polymer nanotechnology: Nanocomposites

For the last decades, nanocomposites materials have been widely studied in the scientific literature as they provide substantial properties enhancements, even at low nanoparticles content. Their performance depends on a number of parameters but the nanoparticles dispersion and distribution state remains the key challenge in order to obtain the full nanocomposites’ potential in terms of, e.g., flame retardance, mechanical, barrier and thermal properties, etc., that would allow extending their use in the industry. While the amount of existing research and indeed review papers regarding the formulation of nanocomposites is already significant, after listing the most common applications, this review focuses more in-depth on the properties and materials of relevance in three target sectors: packaging, solar energy and automotive. In terms of advances in the processing of nanocomposites, this review discusses various enhancement technologies such as the use of ultrasounds for in-process nanoparticles dispersion. In the case of nanocoatings, it describes the different conventionally used processes as well as nanoparticles deposition by electro-hydrodynamic processing. All in all, this review gives the basics both in terms of composition and of processing aspects to reach optimal properties for using nanocomposites in the selected applications. As an outlook, up-to-date nanosafety issues are discussed.

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Review on the Processing and Properties of Polymer Nanocomposites and Nanocoatings and Their Applications in the Packaging, Automotive and Solar Energy Fields.

Rod-like silicates (attapulgite, ATT) with covalently grafted polymer chains chemically identical to the matrix were incorporated into polyimide films, which resulted in prominent improvements in strength and toughness and elevation as high as 51 °C of the thermal decomposition temperature. The dispersion uniformity of ATT nanorods in the polyimide was confirmed by SEM observations and UV-vis spectra. High grafting efficiency of the polymer on the particle surface significantly confines the segmental motion of the polyimide, causing a 33 °C increase in the glass transition temperature and remarkable broadening in the primary transition of nanocomposite films. The decreases in strength and toughness of the samples with high particle contents indicate that there are other factors impacting the mechanical properties of nanocomposites, besides percolated particle networks and attractive interfacial interactions. The plastic deformation observed on the fracture surface of nanocomposites suggests that the introduction of free volume, due to the exclusive volume effect of particles and polymer chains, might play a crucial role especially for those samples with high particle contents. Some fundamental facts based on the free volume effect are proposed to elucidate the possible reasons why the strength and toughness of nanocomposites decrease at high particle contents, which implies that there probably exists a limit upon simultaneously reinforcing and toughening a polymer matrix by means of adding nanoparticles. Similarly, such a limit probably impairs the improvement in thermal stability of nanocomposites at high particle contents, although the segmental confinement effect and porous feature of rod-like silicates have led to pronounced improvements in the thermal stability of the polyimide.

Rod-like attapulgite/polyimide nanocomposites with simultaneously improved strength, toughness, thermal stability and related mechanisms

Self-lubricating polymer composite coatings, with tailorable tribological and mechanical properties, have been widely employed on mechanical parts to reduce friction and wear, which saves energy and improves the overall performance for applications such as aerospace satellite parts, shafts, gears, and bushings. The addition of functional fillers can overcome the limitations of single-polymer coatings and extend the service life of the coatings by providing a combination of low friction, high wear resistance, high load bearing, high temperature resistance, and high adhesion. This paper compares the heat resistance, and the tribological and mechanical properties of common polymer matrices, as well as the categories of functional fillers that improve the coating performance. Applicable scopes, process parameters, advantages, and limitations of the preparation methods of polymer coatings are discussed in detail. The tribological properties of the composite coatings with different matrices and fillers are compared, and the lubrication mechanisms are analyzed. Fillers reduce friction by promoting the formation of transfer films or liquid shear films. Improvement of the mechanical properties of the composite coatings with fillers of different morphologies is described in terms of strengthening and toughening mechanisms, including a stress transfer mechanism, shear yielding, crack bridging, and interfacial debonding. The test and enhancement methods for the adhesion properties between the coating and substrate are discussed. The coating adhesion can be enhanced through mechanical treatment, chemical treatment, and energy treatment of the substrate. Finally, we propose the design strategies for high-performance polymer composite coating systems adapted to specific operating conditions, and the limitations of current polymer composite coating research are identified.

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A review on tribology of polymer composite coatings

The purpose of the present study is to compare the effects of different kinds of fibers on the mechanical and tribological properties (in dry conditions) of a phenolic resin–based friction material. The series of fibers used in the study include rockwool, ceramic, E-glass, and steel wool fibers. The fiber volume fraction in all composites was kept constant at 30%. Tribological studies were performed on a pin-on-disc apparatus at sliding speeds of 3.2–12.8 m/s, disc temperatures of 100–350°C, and applied loads of 312.5–625 N. Experiments showed that the friction coefficient in general decreased with increasing sliding speed and applied load but increased with increasing disc temperature up to 300°C and then decreased above this temperature. The specific wear rate was found to increase with increasing sliding speed and disc temperature. The highest friction coefficient and specific wear rate were obtained with E-glass and steel wool fiber–reinforced composites, respectively. The wear mechanism was also anal...

Effects of Different Kinds of Fibers on Mechanical and Tribological Properties of Brake Friction Materials

A study on attapulgite reinforced PA6 composites

The blends of polyamide (PA) and ultra high molecular weight polyethylene (UHMWPE) were prepared by a Brabender DSE25 co-twin screw extruder, and maleic anhydride (MAH) grafted high-density polyethylene (HDPE) was used as a compatibilizer. A chemical reaction between MAH group of MAH-g-HDPE and terminal amino group of PA was testified by FT-IR analysis. Mechanical and tribological tests showed that the tensile and bending strength of PA decrease with the increase of UHMWPE. Besides, the mechanical strengths of PA/UHMWPE blends were improved by adding appropriate MAH-g-HDPE. The chemical reaction between MAH-g-HDPE and PA ameliorated the homogeneous dispersing ability of UHMWPE in the blend. The friction coefficient and volume wear rate of the PA/UHMWPE blends decreased apparently with the increase of UHMWPE, as was probably that UHMWPE has straight chain structure and good flexibility; therefore, a transferring film could be easily formed on the steel surface with the increase of UHMWPE. In friction process, the wear resistance of the blends was relative to the mechanical property of the blends when the amount of the transferring layer reached to a certain value. POLYM. ENG. SCI., 47:738–744, 2007. © 2007 Society of Plastics Engineers.

Mechanical and tribological behaviors of polyamide 66/ultra high molecular weight polyethylene blends

Polyamide 66(PA66)/clay nanocomposites were prepared by direct melt compounding. The mechanical and tribological properties were evaluated. It was found that addition of clay into PA66 increased the bending strength and microhardness of PA66. And also, the incorporation of clay can reduce the friction coefficient of PA66. The nanocomposites which have the mass fraction less than 5% show less wear rate compared with neat PA66. High fraction of clay can cause severe agglomerated abrasives. The differences in the friction and wear behaviors of PA66 and PA66/clay nanocomposites are attributed to the differences in their surface morphologies, transfer film characteristic. The agglomerated abrasives on the worn surface contribute to the increase of wear rate of nanocomposites of higher mass fraction clay. The friction and wear behaviors of PA66 and its nanocomposites under high temperature exhibit similar tendency with those under 25°C. POLYM. ENG. SCI., 48:203–209, 2008. © 2007 Society of Plastics Engineers

The friction and wear properties of clay filled PA66

Polyamide 66(PA66)/montmorillonite nanocomposites were prepared via direct melt compounding. The nonisothermal crystallization of PA66 and PA66/MMT nanocomposites were investigated by differential scanning calorimetry. The results show that MMT platelets play a competing role in the crystallization process of nylon 66. On the one hand, they can act as a nucleator for the PA66 matrix, accelerating the crystallization rate; on the other hand, they retard the crystal/spherulite growth, especially for nanocomposites with higher MMT content. The analysis results using Jeziorny and Mo equations verify the dual actions of the nucleation and the obstruction of crystallization of MMT in the PA66 matrix. Kissinger's method was used to obtain the activation energy of the crystallization process; the results confirm that the incorporation of MMT causes the above actions.

Nonisothermal Crystallization Kinetics of Nylon 66/Montmorillonite Nanocomposites

Super‐tough nylon 6/ABS blends were prepared by using styrene/acrylonitrile/maleic anhydride co‐polymer (SAM) as a compatibilizer. The variations in morphology, mechanical behavior, and crystallinity associated with the reaction of the SAM with the nylon were characterized. The results showed that the addition of SAM to nylon 6/ABS blends enhanced the interfacial adhesion between nylon 6 and ABS, and this led to the decrease of ABS domain size and the improvement of mechanical properties of their blends. Moreover, it could be found that the crystallinity and phase morphology changed with the variation of SAM.

Morphological, Thermal and Mechanical Properties of Compatibilized Nylon 6/ABS Blends

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