Mohd Shahneel Saharudin

The degradation of mechanical properties in polymer nano-composites exposed to liquid media – a review

The advancement of polymer nano-composites has been motivated by the need for materials with a specific combination of mechanical properties beyond those achieved from only one material. Integration of reinforcement into polymers at the nanoscale can provide a significant increase in numerous physical and mechanical properties of polymer nano-composites. However, in applications where contact with liquid media is unavoidable, the mechanical properties of polymer nano-composites suffer degradation which is a commonly observed phenomenon. Non aggressive liquid such as water is capable of lowering the mechanical properties of polymer nano-composites by acting as plasticizers while moderate and severe aggressive liquid when combined with residual stresses can cause unexpected brittle failure known as ESC. To date, only a few studies are reported discussing the ability of nano-fillers to resist degradation of mechanical properties in polymer nano-composites when exposed to liquid media. In this review, various factors responsible for mechanical property degradation caused by liquid media in polymer nano-composites and their remedies are studied.

The Influence of Alumina Filler on Impact Properties of Short Glass Fiber Reinforced Epoxy

mpact resistance is one of the main consideration in measuring service life, liability and safety of polymer composite structures or products. Impact resistance of a composite material can be measured in terms of energy absorption, depth of penetration and total impact time. In this study, the influence of alumina Al2O3 on impact properties of short glass fiber reinforced polymer was investigated. The drop weight impact tests were performed in accordance to ASTM D7136 standard using Dynatup impact tester. Based on the results, the incorporation of micronsize alumina filler enhanced the energy absorbed during crushing, reduced the depth of penetration of the impactor and expanded the total impact time hence improved the impact properties of the composites.

N,N-Dimethylformamide (DMF) usage in epoxy/graphene nanocomposites: problems associated with reaggregation

DMF is one the most commonly-used solvents for preparing graphene nanocomposites. Various processing variables for DMF are being used for the preparation of epoxy/graphene nanocomposites. Whilst the emphasis of all of these reported studies are on the improvements in mechanical, and other properties, of the epoxy/graphene nanocomposites, there is no study investigating how DMF affects the processing and how it is associated with the final properties of the nanocomposites. In this work, different dosages of DMF have been used to prepare nanocomposites. Mechanical testing, X-ray diffraction (XRD), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) have been used to analyze the effectiveness of DMF dosage on the properties of processed nanocomposites. Larger dosages of DMF are not always ideal for dispersing graphene as it promotes reaggregation of graphene during the processing.

The Degradation of Mechanical Properties in Halloysite Nanoclay-Polyester Nanocomposites Exposed in Seawater Environment

Polyester based polymers are extensively used in aggressive marine environments; however, inadequate data is available on the effects of the seawater on the polyester based nanocomposites mechanical properties. This paper reports the effect of seawater absorption on the mechanical properties degradation of halloysite nanoclay-polyester nanocomposites. Results confirmed that the addition of halloysite nanoclay into polyester matrix was found to increase seawater uptake and reduce mechanical properties compared to monolithic polyester. The maximum decreases in microhardness, tensile and flexural properties, and impact toughness were observed in case of 1 wt% nanoclay. The microhardness decreased from 107 HV to 41.7 HV 61% decrease. Young’s modulus decreased from 0.6 GPa to 0.4 GPa 33% decrease. The flexural modulus decreased from 0.6 GPa to 0.34 GPa 43% decrease. The impact toughness dropped from 0.71 kJ/m2 to 0.48 kJ/m2 32% decrease. Interestingly, the fracture toughness KIC increased with the addition of halloysite nanoclay due to the plasticization effect of the resin matrix. SEM images revealed the significant reduction in mechanical properties in case of 1 wt% reinforcement which is attributed to the degradation of the nanoclay-matrix interface influenced by seawater absorption and agglomeration of halloysite nanoclay.

The degradation of mechanical properties in halloysite nanoclay–polyester nanocomposites exposed to diluted methanol

The degradation of mechanical properties in halloysite nanoclay–polyester nanocomposites was studied after an exposure of 24 h in diluted methanol system by clamping test specimens across steel templates. The glass transition temperature (Tg) and storage modulus increased steadily with the increase of halloysite nanoclays before and after diluted methanol exposure. The addition of nano-fillers was found to reduce liquid uptake by 0.6% in case of 1 wt% reinforcement compared to monolithic polyester. The mechanical properties of polyester-based nanocomposites were found to decrease as a result of diluted methanol absorption. After diluted methanol exposure, the maximum microhardness, tensile, flexural and impact toughness values were observed at 1 wt% of halloysite nanoclay. The microhardness increased from 203 to 294 HV (45% increase). The Young’s modulus increased from 0.49 to 0.83 GPa (70% increase) and the tensile strength increased from 23 to 27 MPa (17.4% increase). The impact toughness increased from 0.19 to 0.54 kJ/m2 in diluted methanol system (184% increase). Surprisingly, the fracture toughness of all types of nanocomposites was found to increase after exposing to diluted methanol due to plasticization effect. Scanning electron microscope images of the fractured surfaces of tensile specimens revealed that the methanol increased the ductility of the matrix and reduced the mechanical properties of the nanocomposites.

Effect of Short-Term Water Exposure on the Mechanical Properties of Halloysite Nanotube-Multi Layer Graphene Reinforced Polyester Nanocomposites

The influence of short-term water absorption on the mechanical properties of halloysite nanotubes-multi layer graphene reinforced polyester hybrid nanocomposites has been investigated. The addition of nano-fillers significantly increased the flexural strength, tensile strength, and impact strength in dry and wet conditions. After short-term water exposure, the maximum microhardness, tensile, flexural and impact toughness values were observed at 0.1 wt % multi-layer graphene (MLG). The microhardness increased up to 50.3%, tensile strength increased up to 40% and flexural strength increased up to 44%. Compared to dry samples, the fracture toughness and surface roughness of all types of produced nanocomposites were increased that may be attributed to the plasticization effect. Scanning electron microscopy revealed that the main failure mechanism is caused by the weakening of the nano-filler-matrix interface induced by water absorption. It was further observed that synergistic effects were not effective at a concentration of 0.1 wt % to produce considerable improvement in the mechanical properties of the produced hybrid nanocomposites.

Dichlorobenzene: an effective solvent for epoxy/graphene nanocomposites preparation

It is generally recognized that dimethylformamide (DMF) and ethanol are good media to uniformly disperse graphene, and therefore have been used widely in the preparation of epoxy/graphene nanocomposites. However, as a solvent to disperse graphene, dichlorobenzene (DCB) has not been fully realized by the polymer community. Owing to high values of the dispersion component (δd) of the Hildebrand solubility parameter, DCB is considered as a suitable solvent for homogeneous graphene dispersion. Therefore, epoxy/graphene nanocomposites have been prepared for the first time with DCB as a dispersant; DMF and ethanol have been chosen as the reference. The colloidal stability, mechanical properties, thermogravimetric analysis, dynamic mechanical analysis and scanning electron microscopic images of nanocomposites have been obtained. The results show that with the use of DCB, the tensile strength of graphene has been improved from 64.46 to 69.32 MPa, and its flexural strength has been increased from 97.17 to 104.77 MPa. DCB is found to be more effective than DMF and ethanol for making stable and homogeneous graphene dispersion and composites.

Effects of surfactants on the properties of epoxy/graphene nanocomposites:

Recently, graphene has attracted extensive research interests due to its superior mechanical, electrical and thermal performance. Small loadings of graphene can increase the properties of epoxy significantly. However, because of the large surface area of graphene, it is a challenge to disperse graphene in liquid epoxy. Strong van der Waals force causes reaggregation of graphene in the matrix. As commonly used surfactants, sodium dodecyl sulphate and gum arabic have been used a lot to de-bundle graphene, however, their dispersing efficiencies for graphene in epoxy matrix is unknown. Therefore, to evaluate their dispersing efficiencies, epoxy/graphene nanocomposites had been made and mechanical properties, dynamic mechanical analysis, thermal gravimetric analysis and scanning electron microscopy tests of nanocomposites had been conducted. The results show that the properties of nanocomposites had been enhanced largely after using sodium dodecyl sulphate and gum arabic. Sodium dodecyl sulphate shows higher dispersing effectiveness than gum arabic.

Biodegradation of Halloysite Nanotubes-Polyester Nanocomposites Exposed to Short Term Seawater Immersion

Halloysite nanotubes (HNTs)-polyester nanocomposites with four different concentrations were produced using solution casting technique and the biodegradation effect of short-term seawater exposure (120 h) was studied. Monolithic polyester was observed to have the highest seawater absorption with 1.37%. At 0.3 wt % HNTs reinforcement, the seawater absorption dropped significantly to the lowest value of 0.77% due to increase of liquid diffusion path. For samples tested in dry conditions, the Tg, storage modulus, tensile properties and flexural properties were improved. The highest improvement of Tg was from 79.3 to 82.4 °C (increase 3.1 °C) in the case of 0.3 wt % HNTs. This can be associated with the exfoliated HNTs particles, which restrict the mobility of polymer chains and thus raised the Tg. After seawater exposure, the Tg, storage modulus, tensile properties and flexural properties of polyester and its nanocomposites were decreased. The Young’s modulus of 0.3 wt % HNTs-polyester dropped 20% while monolithic polyester dropped up to 24% compared to their values in dry condition. Apart from that, 29% flexural modulus reduction was observed, which was 18% higher than monolithic polyester. In contrast, fracture toughness and surface roughness increased due to plasticization effect. The presence of various microbial communities caused gradual biodegradation on the microstructure of the polyester matrix as also evidently shown by SEM images.