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Polymers and Polymer Composites

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Title: Porosity effect on residual flexural strength following low energy impact of carbon fibre composites
Page Range: p.205-212
Author(s): Arthurs B; Bull D J; Arumugam V; Chambers A R; Santulli C
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.4

Abstract
Studies of the combined effects of the presence of porosity (as it may result from partially effective cure cycles) and of low-energy impact damage on the residual properties of CFRP laminates have led so far to controversial results. In particular, it is not clear from the literature whether the presence of voids would blunt crack propagation following impact or rather would promote damage development. These effects would respectively either increase or reduce post-impact residual strength, relative to that of the laminate with virtually no voids, as the result of an optimal manufacturing procedure. With this in mind, different cure cycles have been applied to produce carbon fibre-reinforced polymer (CFRP) composites with various levels of void content, which were subjected to low energy impact damage (3, 4.5 and 6 J) and then to post-impact flexural strength measurement. Damage assessment using micro-focus computed tomography ((mu)CT) was used to complement traditional ultrasonic C-scans, which proved ineffective on the high-porosity samples. Three cure-cycles were investigated: one which led to high porosity (average void content 4 vol%) and two conventional low-porosity cure cycles, only one of which included a post-cure cycle. This study has found that, despite a lower initial flexural strength, higher residual flexural strength was retained after impact in the high-porosity material than in the low-porosity one. This is explained by the lower extent of impact damage observed in the high porosity material, where voids had the effect of suppressing delamination propagation. 23 Refs.

Title: Reinforcement role of carbon nanotubes: interfacial properties of carbon fibre - epoxy nanocomposite
Page Range: p.213-222
Author(s): Min Ya; Ryszard Pyrz
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.4

Abstract
Single-walled carbon nanotube (SWCNT) reinforced epoxy was fabricated as the matrix material for carbon fibre reinforced composite. SWCNT-epoxy sample with a single fibre on the top of the surface was loaded incrementally to sufficient strain levels to cause interfacial failure. Fibre strain profiles were obtained at each level of the applied strain by Raman spectroscopy. The strain distributions obtained agree well with the Cox shear-lag model and Piggott partial-debonding model that are conventionally used to describe load transfer at interface. No full-debonding phenomenon was observed. Interfacial shear stress (ISS) distribution was derived at each applied matrix strain. Interfacial shear strength (IFSS) increases after introducing SWCNT in the epoxy resin, which can be explained by the increase of shear yield stress of the matrix material and the increase of radial pressure at the interface resulting from thermal residual stress. The residual strains in the matrix in the vicinity of the single carbon fibre were also mapped by using of the Raman spectra of SWCNT. Stress concentration zones were observed around the fibre ends. 19 Refs.

Title: Preparation and characterization of poly(2-hydroxyethyl methacrylate) and castor oil based uralkyds interpenetrating polymer networks
Page Range: p.223-228
Author(s): Prashantha K; Rashmi B J; Vasanth Kumar Pai K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.4

Abstract
Interpenetrating polymer networks (IPNs) of poly[2-hydroxyethylmethacrylate] and uralkyd prepolymer were synthesised using benzoyl peroxide as initiator, polyethylene glycol as chain extender, and N,N-methylene bis acrylamide as crosslinker by sequential polymerisation method. The concentration of uralkyd (UA) prepolymer and poly[2-hydroxyethylmethacrylate] (PHEMA) were varied and their effects on chemical, mechanical, thermal, and morphological properties of IPNs were investigated. The IPNs glass-transition temperatures increase with increasing PHEMA concentrations. Tensile strength, and shore A hardness increases with increasing concentration of PHEMA while sacrificing percent elongation. Almost all IPNs have shown similar chemical resistance irrespective of composition. Thermo gravimetric analysis (TGA) indicated that increase in PHEMA concentration increases thermal stability of IPNs. Morphological analysis reveals that IPNs reveals heterogeneous and compact morphologies with distinct microphase separation. 22 Refs.

Title: Comparison of effects of alkali treatment on flax fibre reinforced polyester and polyester-biopolymer blend resins
Page Range: p.229-242
Author(s): Mahesh Hosur; Harika Maroju; Shaik Jeelani
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.4

Abstract
In this study, flax fibres were treated initially with a 2.5, 5, and 7% of sodium hydroxide (NaOH) solution at room temperature for one hour. Among different treatments, fibres treated with 2.5% alkali solution showed optimal properties. Hence, for further studies, all flax fibres were treated with 2.5% solution of alkali solution, but at different temperatures. In the next phase of study, biocomposites were prepared by immersing fibre mats in resin bath and compression moulding using a hot press. Two polymers: polyester and a polyester-biopolymer blend, Envirez (Registered) 1807 were used as matrices. Moisture absorption and flexure tests were conducted on the composites. It was determined that composites with treated fibres showed reduction in moisture uptake compared to those with untreated fibres. Composites with alkali treated fibres showed an increase in flexural properties as well as storage modulus which was attributed to effects of chemical treatment. Composites made using Envirez (Registered) 1807 which has about 22% of natural polymer showed comparable properties with those made using polyester resin system. 28 Refs.

Title: Synthesis and characterization of star-shaped poly(lactideco-glycolide) using POSS as an initiator, and its drug-loaded microspheres
Page Range: p.243-250
Author(s): Xiaojing Zhang; Chong Li; Yuelei Hu; Jiashu Sun; Shaoming Fang
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.4

Abstract
In this paper, a series of star-shaped poly(lactide-co-glycolide)s (sPLGA) with different block ratios were prepared by the ring-opening copolymerisation of D,L-lactide (LA) and glycolide (GA) with multi-hydroxyl polyhedral oligomeric silsesquioxane core as an initiator and tin (II) 2-ethylhexanoate (Sn(Oct)2) as the catalyst. The products were characterised by NMR, FT-IR, GPC, XRD, DSC, TGA and viscosity measurements. The results show that the contents of PLA and PGA segments in sPLGA can be controlled by the feed ratios of the copolymerisation. The glass transition temperature and crystallinity of sPLGA decrease and the crystalline sPLGA becomes amorphous with increasing the molar feed ratio between GA and LA from 10:90 to 50:50. The drug-loaded sPLGA microspheres were prepared by an emulsion solvent evaporation method. The morphology and the drug release property were investigated by SEM, dynamic light scattering (DLS) and ultraviolet spectrophotometry (UV). The results indicate that the sPLGA80 microsphere surface was smooth and the mean diameter was about 1.27(mu)m. The sPLGA80 microspheres showed good drug loading and release properties. 32 Refs.

Title: Theoretical models and experimental study on mechanical properties of reinforced polymer matrix using different kinds of carbon nanotubes
Page Range: p.251-260
Author(s): Kordani N; Adibipour R; Sadough Vanini A; Zare A; Gil V
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.4

Abstract
This paper is a study of the role of functionalised multi-walled carbon nanotubes (MWCNT-COOH) and single-walled carbon nanotubes (SWCNT) in improving the mechanical properties of epoxy resins. In nanotube-based polymeric composite it is anticipated that high elastic modulus can be achieved by taking advantage of the interfacial friction between the nanotubes and the polymer. In order to evaluate the CNT effect on polymer composites, different weight fractions of CNTs and two different kinds of CNTs were dispersed in the matrix. First, the damping characteristics of the samples with 0, 0.5, 1 and 1.5 wt.% nanotube contents were measured and then the tensile modulus was determined experimentally. The experiments showed an increase of the elastic modulus and the damping due to adding CNTs. Theoretical models were used to show the effect of added reinforcement to compare with experimental elastic modulus data. The results showed that a modified Rule of Mixtures model, incorporating the effect of fibre orientation in 3D was closest to the experimental results. 29 Refs.

Title: Thermal stability of electrical properties and amine vapour sensitivity of in-situ prepared polyaniline/graphene nanocomposites assisted by sodium dodecyl sulfate micelles
Page Range: p.261-270
Author(s): Tarique Anwer; Faiz Mohammad
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.4

Abstract
Polyaniline (Pani)/graphene (GN) nanocomposites were prepared by in-situ oxidative polymerisation of aniline with GN in presence of sodium dodecyl sulphate. The effects of polymerisation and modification of the chemical structures in the nanocomposites were characterised by fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction techniques (XRD). Sodium dodecyl sulphate played the role of a surfactant, improving the dispersion of GN within the polymer matrix simultaneously. FTIR results revealed the presence of (pi)^-(pi) interactions between Pani and GN leading to the formation of a charge-transfer complex. The thermal stabilities of the electric properties of the as-prepared nanocomposites were investigated as a function of GN content. As-prepared Pani/GN nanocomposites showed greater electrical conductivity as well as improved thermal stability in terms of DC electrical conductivity retention under isothermal and cyclic ageing conditions compared with pure Pani. They were also observed to possess better amine sensing properties in comparison to pure Pani when exposed to the vapour of methylamine. 21 Refs.

Title: The synergistic effects of carbon black and carbon fibre on the thermal conductivity of silicone rubber
Page Range: p.271-276
Author(s): Jibin Wang; Luping Ni; Qiuying Li; Chifei Wu
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.4

Abstract
Silicone rubber (SR) composites filled with carbon black (CB) and carbon fibre (CF) were prepared. The effects of a single filler as well as hybrid fillers on the thermal conductivity (a) and mechanical properties of SR composites were investigated. It was found that hybrid filler was more effective in increasing ww of the composite, and this effect was more pronounced when the weight ratio of CF:CB was 80:20. The scanning electron microscopy showed the hybrid filler formed a better filler network than single filler in the matrix. SR composites filled with hybrid fillers also possessed better mechanical properties compared with composites filled with only CF. 36 Refs.

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