Polymer Composites

Carbon-based polymer composites have acquired significant attention due to their outstanding properties. In this chapter, we analyse the most interesting characteristics of this type of polymer composites, from the structural to the applicative point of view. In particular, we will focus on the characteristics of carbon nanotubes and expanded graphite and on the electrical conductivity mechanisms. Piezoresistive properties of the composites are discussed with the aim to highlight their promising applications in the field of deformation-sensing devices.

This study investigated the effects of organoclay platelet contents (0, 3 and 5 wt%) and polypropylene type (virgin and recycled) on the mechanical properties of polypropylene/wood flour composites. Composite samples were made by melt compounding and consequent injection moulding. The tensile, flexural and impact properties of resultant composites were determined. X-ray diffraction (XRD) analysis of composites with 3 and 5% nanoclay content was also conducted. The results indicated that tensile and flexural properties of the composites increased with the addition of nanoclay particles up to 3 wt% and decreased thereafter. The impact strength of the composites, however, decreased with the incorporation of nanoclay. The mechanical properties of the recycled polypropylene-based nanocomposites were statistically comparable with those based on virgin polypropylene. XRD analysis revealed that the degree of intercalation in the nanocomposites containing 3% nanoclay was higher than in those containing 5%. Based on these results, it can be concluded that recycled polypropylene could be used instead of virgin polypropylene in the production of value-added products with no significant adverse effects on the mechanical properties.

The growing need of eco-friendly product manufacturing led to the development of natural fiber composite to suit various applications in the field of Automobile interior parts, construction and manufacturing. Composite material is a material composed of two or more distinct phases (matrix phase and dispersed phase) and having bulk properties significantly different from those of any of the constituents. In this study, the composite materials are reinforced with natural fibers such as Jute, Sisal, Banana, and Palmyra in the Epoxy (LY 556) Matrix. The impressive mechanical properties led to the selection of these fibers for the study. Hand lay-up technique was used for the preparation of composites. Hybrid fiber mates were also prepared using all these fibers. The mechanical properties such as tensile strength, compressive strength, flexural strength and impact strength were determined and compared for the different combinations.

ABSTRACT: The aim of present experimental investigation is to compare the mechanical properties of Sisal, jute and kenaf fiber reinforced with glass fiber in polyester matrix hybrid composites. Hybrid composites were fabricated by hand lay-up technique. The tensile, flexural and impact tests were carried out on different composite samples as per the ASTM standards. It was observed that the tensile strength of jute/glass fiber composite is 1.94 and 1.59 times more than that of sisal/glass and kenaf/glass composites, respectively. The flexural load carrying capacity of sisal/glass composite is 3.4 and 2.83 times greater than those of jute/glass and kenaf/glass composites, respectively. Also, it can be seen that impact strength of jute/glass composite is almost equal to that of kenaf/glass composite and 1.13 times more than that of sisal/glass composite.

Novel poly (ε-caprolactone)/poly(lactic acid), (PCL/PLA, ratio 90:10) blend composites were prepared with mercerized palm press fibers by melt extrusion and injection molding. The normal soil burial method was used to study the composites biodegradation. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) was employed to study the crystallinity of the blend composites while Dynamic mechanical analysis (DMA) confirmed the glass transition temperature of the composites. Compatibilization using dicumyl peroxide (DCP, 0.01phr) and fiber reinforcement accelerated the rate of biodegradation of the blend composites. The rate of biodegradation increased as fiber load increased from 10 wt% to 25 wt% in the composites. This was confirmed by the residual weights of the composites over the 90 days burial period. The DSC and XRD results showed that compatibilization reduced the melting temperature and crystallinity of the blends respectively. The DMA results confirmed the Tg of the blends composites to be around -62 oC. However, incorporating fibers from 10 wt% to 20 wt% enhanced the crystallinity of the compatibilized blend composites.

"Production techniques,  structure, and electrochemical  properties of  conducting  thin-film  materials
consisting of  a polyethylene (PE)  substrate  covered with a polyacetylene (PA)  layer  are studied.  Properties of
a  free  PA  film  are  determined  by the  catalyst used in  its synthesis.  Properties  of  composites  depend on the  opti-
mum selection  of  the  PA/PE  ratio (by  weight), the  catalyst used for  polymerizing  PA,  and  the  PE structure.  The
capacity  of  composites  is  higher  than  that  of  free  PA  films.  This points to  the  possible  role  of  an  increased  trans-
port of  lithium  cations  at interfaces."

"Organic polymers have such useful properties as durability, easy processibility, low density, and a  rather low cost. One  more  property, namely electrical conductivity of the polymers with conjugated double bonds, was unexpected. Attempts to combine the properties of metals (conductivity) and those of polymers mentioned above were made for a long time. Mechanical mixing of powders of a metal or graphite with polymers could  not give a  material  with high parameters  without a  deterioration of electrical conductivity or economic utility. Increasing  the metal content results in an increase in conductivity but raises the cost of the product and lowers the mechanical parameters inherent in  polymers [I]. A new class of organic polymers  that  conduct  an  electrical  current,  which  are  sometimes  called "organic
metals," occupies an intermediate  position between semiconductors and  metals in the 10-9-l@ S/cm range"

A simple tapered plastic optical fiber (POF) sensor is proposed and demonstrated for the detection of uric acid concentrations in deionized water. The sensor uses a tapered POF probe coated with different concentrations of graphene in a polymer composite. The tapered fiber is fabricated using an etching method and has a waist diameter of 0.45 mm and tapering length of 10 mm. The coating improves the sensitivity of the proposed sensor as it changes the effective refractive index of the cladding and allows more lights to be transmitted from the tapered fiber. The probe is immersed in uric acid solution and it senses the relative acid concentration using intensity modulation technique. As the uric acid concentration varies from 0 to 500 ppm, the output voltage of the sensor increases linearly from 2.98 to 4.36 mV with a sensitivity of 0.0021 mV/ppm and a linearity of more than 98.88%. A more efficient and stable sensor with graphene polymer composite coating increases the sensitivity due to the effective refractive index of the deposited cladding that allows more light to be transmitted through the tapered fiber. © 2014 IEEE.

http://ieeexplore.ieee.org/ielx7/7361/6766215/06727412.pdf?tp=&arnumber=6727412&isnumber=6766215 

Polymethylmethacrylate (PMMA) and functionalized
multiwalled carbon nanotube (F-MWCNT) based composite
films were prepared using solution casting
method. Nanoindentation and scratch measurements
were carried out to study the influence of F-MWCNT as
the reinforcement on the mechanical properties of the
composite at the sub-micron scale. The composites
were prepared with varying weight percentages of
F-MWCNT in the PMMA matrix. The composites containing
an adequate amount (0.25 wt%) of F-MWCNT
was found to demonstrate the maximum nanomechanical
properties, viz. hardness, elastic modulus, recovery
index. Scratch resistance measured in terms of
coefficient of friction, also showed maximum value for
the PMMA composite reinforced with 0.25 wt% of
F-MWCNT.

Elastic instabilities, when properly implemented within soft, mechanical structures, can generate advanced functionality. In this work, we use the voltage–induced buckling of thin, flexible plates to pump fluids within a microfluidic channel. The soft electrodes that enable electrical actuation are compatible with fluids, and undergo large, reversible deformations. We quantified the onset
of voltage-induced buckling, and measured the flow rate within the microchannel. This embeddable, flexible microfluidic pump will aid in new generation of stand-alone microfluidic devices that require a tunable flow rate.