Forming performance and biodegradability of woodfibre–Biopol™ composites

A Taguchi approach to experimental design has been used to analyse the hotpressing and vee-bending of woodfibre–Biopol™ composites. Analysis of the hotpressing process clearly shows that platen temperature is the parameter with the most influence on tensile performance of the composite sheet produced. In bending (a common manufacturing situation), geometric conformance is maximised when forming time is 60 s, forming rate is 250 mm/min and forming radius/thickness ratio is 2 for the composite sheets studied in this paper. A study of the influence of fibre volume fraction on the biodegradability of these sheets show that these composites are highly biodegradable, often degrading at a rate greater than that of pure Biopol™. The results also suggest that a woodfibre mass fraction of ∼15% maximises the degradation of the woodfibre–Biopol™ composites.     

Preparation and characterization of polypropylene–wheat straw–clay composites

Preparation of polypropylene hybrid composite consisting of wheat straw and clay as reinforcement materials was investigated. The composite samples were prepared through melt blending method using a co-rotating twin-screw extruder. The composition of constituents of hybrid composite such as percentages of wheat straw, clay and maleic anhydride grafted polypropylene as a coupling agent was varied in order to investigate their influence on water absorption and flexural properties. The XRD analysis of composite samples containing clay showed shift in d₀₀₁ peak to lower 2θ indicating slight intercalation of polymer in clay sheets. The results of the study indicate that the increase in wheat straw and clay content in a composite increases the flexural modulus and reduces the resistance for water absorption. The increase in PP-MA coupling agent also increases the flexural modulus and resistance for water absorption. The morphological study by scanning electron microscope reveals that the addition of coupling agent increases the interfacial adhesion between the fibers and polymer matrix which is evidenced further from increased flexural modulus. Further, the particle size of wheat straw was analyzed before and after extrusion in order to investigate the effect of extrusion on wheat straw dimensions. The addition of clay as additional filler had no significant role on water absorption and flexural properties of the composite.     

Accelerated weathering of fire-retarded wood–polypropylene composites

In this study, the influence of fire retardants, namely aluminum trihydrate, zinc borate, melamine, graphite, titanium dioxide on the durability of polypropylene-based co-extruded wood–plastic composites is studied. The composites underwent accelerated weathering under a xenon-arc lamp source during 1000 h. FTIR analysis of the composite surface revealed a degradation process which was accompanied by chemical changes, including vinyl-like and carbonyl groups accumulation; fire retardants did not influence the photo-oxidation mechanism of the composite. Fire retardant-loaded samples had smaller color change compared to the unfilled one. The tensile properties of all composites declined after the weathering. Significant changes in the surface morphology of the weathered composites were observed with a scan electron microscope.     

Structure–property relationships in biaxially deformed polypropylene nanocomposites

Semi-solid forming processes such as thermoforming and injection blow moulding are used to make much of today’s packaging. As for most packaging there is a drive to reduce product weight and improve properties such as barrier performance. Polymer nanocomposites offer the possibility of increased modulus (and hence potential product light weighting) as well as improved barrier properties and are the subject of much research attention. In this particular study, polypropylene–clay nanocomposite sheets produced via biaxial deformation are investigated and the structure of the nanocomposites is quantitatively determined in order to gain a better understanding of the influence of the composite structure on mechanical properties. Compression moulded sheets of polypropylene and polypropylene/Cloisite 15A nanocomposite (5 wt.%) were biaxially stretched to different stretching ratios, and then the structure of the nanocomposite was examined using XRD and TEM techniques. Different stretching ratios produced different degrees of exfoliation and orientation of the clay tactoids. The sheet properties were then investigated using DSC, DMTA, and tensile tests .It was found that regardless of the degree of exfoliation or orientation, the addition of clay has no effect on percentage crystallinity or melting temperature, but it has an effect on the crystallization temperature and on the crystal size distribution. DMTA and tensile tests show that both the degree of exfoliation and the degree of orientation positively correlate with the dynamic mechanical properties and the tensile properties of the sheet.     

Accelerated weathering of wood–polypropylene composites containing minerals

Accelerated weathering tests were carried out on wood–polypropylene composites containing minerals. Three different mineral fillers were studied: calcium carbonate, wollastonite and talc. Colour changes were evaluated after distinct periods; the total time of exposure of the composites to UV irradiation was 2000 h. The weathering resulted in significant colour fading of the composites. The composites containing mineral fillers had higher changes of colour (lightness) than the reference composite. Scanning electron microscopy analysis revealed deterioration of the polymer surface layer in all weathered composites. Exposure of the reference composite to UV irradiation resulted in the disappearance of the polypropylene surface layer and disclosure of wood fibres, which led to a higher drop in the lignin content of this composite compared to mineral-containing composites. A substitution of part of the wood with mineral fillers resulted in decreased water absorption and thickness swelling of mineral-containing composites, compared to the reference composite. Exposure to water immersion-freeze–thaw cyclic treatment and UV irradiation led to a decrease in the Charpy impact strength of the composites, except for the composite containing talc.     

Manufacturing sisal–polypropylene composites with minimum fibre degradation

Natural fibres, such as sisal, flax and jute, possess good reinforcing capability when properly compounded with polymers. These fibres are relatively inexpensive, originate from renewable resources and possess favourable values of specific strength and specific modulus. Thermoplastic polymers have a shorter cycle time as well as reprocessability despite problems with high viscosities and poor fibre wetting. The renewability of natural fibres and the recyclability of thermoplastic polymers provide an attractive eco-friendly quality to the resulting natural fibre-reinforced thermoplastic composite materials. Common methods for manufacturing natural fibre-reinforced thermoplastic composites, injection moulding and extrusion, tend to degrade the fibres during processing. Development of a simple manufacturing technique for sisal fibre-reinforced polypropylene composites, that minimises fibre degradation and can be used in developing countries, is the main objective of this study. Composite sheets with a fibre length greater than 10 mm and a fibre mass fraction in the range 15% to 35% exhibited good mechanical properties.     

β-Crystal in injection moulded poly(ethylene terephthalate) fibre/isotactic polypropylene composite

The poly(ethylene terephthalate) (PET) fibre/isotactic polypropylene (iPP) composite was moulded by a mixing-injection moulding machine developed in our group. The molecular orientation and crystallinity of β-crystal were investigated by two-dimensional wide-angle X-ray diffraction (2D-WAXD), and shish-kebab structure was detected by two-dimensional small-angle X-ray scattering (2D-SAXS). In addition, crystalline morphology of β-crystal in different regions was observed by scanning electron microscope (SEM). As well known, PET fibre generally serves as heterogeneous nucleating agent for iPP to induce α-crystal. Unexpectedly, a remarkably increasing crystallinity of β-crystal from skin to core region was obtained in the present work, which is substantially different from other studies. Two origins of β-crystal developed in core region are proposed: (a) local shear caused by the different flow rates of molten iPP and solid PET fibre; (b) survived smectic ordering brought by the rotating screw during plasticization and melt mixing in barrel.     

Optimization of delamination factor in drilling GFR–polypropylene composites

Glass fiber-reinforced polypropylene composites often replace the conventional materials due to their special or unique mechanical properties. As the applications of these composites increase for a number of industries, drilling of these composites is inevitable for subsequent composite product manufacturing stage. In the drilling of composites, the thrust force is induced during the drilling operation; as a result, it causes damage. This damage is characterized by the delamination factor, which depends on the machining parameters such as speed of the spindle, feed rate, and drill diameter. The study on the delamination in the drilling of glass fiber-reinforced polypropylene is limited and has been carried out comprehensively. The effect of machining parameters on delamination in the drilling of glass fiber-strengthened polypropylene (GFR-PP) composites is studied through the Box–Bhenken design. Response surface method, along with the desirability analysis, is used for modeling and optimization of delamination factor in the drilling. The result proves that the models are effectively used to forecast the delamination in the drilling of GFR-PP composites. Also, the result indicates that the foremost issue that influences the delamination is the feed rate.     

Elastomer modified polypropylene–polyethylene blends as matrices for wood flour–plastic composites

Blends of polyethylene (PE) and polypropylene (PP) could potentially be used as matrices for wood–plastic composites (WPCs). The mechanical performance and morphology of both the unfilled blends and wood-filled composites with various elastomers and coupling agents were investigated. Blending of the plastics resulted in either small domains of the minor phase in a matrix of major phase or a co-continuous morphology if equal amounts of HDPE and PP were added. The tensile moduli and yield properties of the blends were clearly proportional to the relative amounts of HDPE and PP in the blends. However, the nominal strain at break and the notched Izod impact energies of HDPE were greatly reduced by adding as little as 25% of the PP. Adding an ethylene–propylene–diene (EPDM) elastomer to the blends, reduced moduli and strength but increased elongational properties and impact energies, especially in HDPE-rich blends. Adding wood flour to the blends stiffened but embrittled them, especially the tougher, HDPE-rich blends, though the reductions in performance could be offset somewhat by adding elastomers and coupling agents or a combination of both.     

Structure–morphology–mechanical properties relationship of some polypropylene/lignocellulosic composites

Natural lignocellulosic materials have an outstanding potential as thermoplastic reinforcement. Polypropylene composites were prepared using different types of lignocellulosic materials by melt blending of 70 wt% polypropylene (PP) and 30 wt% biomasses. The specimens were firstly evaluated for structural and morphological properties by infrared spectroscopy, X-ray diffraction, scanning electron and polarized optical microscopy. Depending on the biomass type, there were evidenced some particular shifts of the infrared bands and also crystallinity changes. An increase in crystallinity is explained by nucleating agent role of biomass. The morphological changes are directly related to variation in mechanical and rheological properties, an increase in Young modulus, melt viscosity and storage and loss moduli being recorded.     

Effect of composition on fracture behavior of polypropylene–wollastonite–polyolefin elastomer system

The fracture behavior of polypropylene (PP)–wollastonite–polyolefin elastomer (POE) in the mixed mode region was studied using the essential work of fracture (EWF) method. The relationship between the microstructure and the fracture parameters was analyzed. The effect of wollastonite content on the essential work of fracture and the work of plastic deformation was discussed. The energy dissipation during a double-edge-notched tension (DENT) test was calculated with the EWF method. It was found in the mixed mode region that σ_n increases with shortening of the ligament length region as plastic constraint effect rises and variation of the specific total work of fracture with ligament length was still reasonably linear within the mixed mode region. With increasing wollastonite content, w _e (specific essential work of fracture) increases, while the βw _p (specific non-essential work of fracture) decreases. The measurements of energy dissipation show that improvement in the fracture toughness of PP–wollastonite–POE is mainly due to the increase in crack propagation resistance during the necking and tearing processes after yielding, while the plastic deformation capability of the material depends mainly on the properties of fracture behavior before yielding. It is also found that the impact strength of the material decreases with increasing wollastonite content. However, the composition with high impact strength has lower specific essential energy of fracture and lower long-term fracture resistance, indicating that EWF is a better indicator of long-term fracture properties than the impact strength. DSC results show that the presence of wollastonite hinders crystallization of the PP.     

β-transcrystallinity developed from the novel ringed nuclei in the glass fiber/isotactic polypropylene composite

Glass fiber (GF) was immersed in diluted acid solution and corroded for 4 h. The interfacial morphology of isotactic polypropylene (iPP) reinforced by the corroded GF was studied via polarized optical microscope. It was found that the corroded GF exhibits anomalous nucleating ability to induce ringed nuclei, and β-transcrystallinity can be developed unexpectedly from these nuclei during isothermal crystallization. The present work provides a novel approach, via which β-transcrystallinity can arise in static condition from the surface of the acid-corroded GF.     

Sol–gel derived composite from bioactive glass–polyvinyl alcohol

Investigation of novel biomaterials for bone engineering is based on the development of porous scaffolds, which should match the properties of the tissue that is to be replaced. These materials need to be biocompatible, ideally osteoinductive, osteoconductive, and mechanically well-matched. In the present paper, we report the preparation and characterization of hybrid macroporous scaffold of polyvinyl alcohol (PVA)/bioactive glass through the sol–gel route. Hybrids containing PVA (80, 70 and 60 wt%) and bioactive glass with composition 58SiO₂–33CaO–9P₂O₅ were synthesized by foaming a mixture of polymer solution and bioactive glass via sol–gel precursor solution. PVA with two different degree of hydrolysis (DH), 98.5% (high degree) and 80% (low degree) were also investigated, in order to evaluate the influence of residual acetate group present in polymer chain on the final structure and properties of 3D porous composite produced. The microstructure, morphology and crystallinity of the hybrid porous scaffolds were characterized by X-ray diffraction (XRD), Infrared Fourier Transform spectrometry (FTIR) and Scanning electron microscopy (SEM/EDX) analysis. In addition, specific surface area was assessed by B.E.T. nitrogen adsorption method and mechanical behavior was evaluated by compression tests. Preliminary cytotoxicity and cell viability were also performed by the MTT assay. VERO cell monolayers were grown in 96-well microtiter plates. The results have clearly showed that hybrid foams of polyvinyl alcohol/bioactive glass (PVA/BG) with interconnected macroporous 3D structure were successfully produced. All the tested hybrids of PVA/BG have showed adequate cell viability properties for potential biological applications.     

Three-phase polymer–ceramic–metal composite for embedded capacitor applications

This paper addresses the materials and processes for printed wiring board compatible embedded capacitor using ceramic, polymer and metal. The Ca[(Li_1/3Nb_2/3)_0.8Ti_0.2]O_3?δ (CLNT)–epoxy–silver, three-phase composites were prepared by two step mixing and thermosetting technique. The dielectric properties of the three-phase composites were investigated in terms of volume fraction of silver, temperature and frequency. The dielectric properties of epoxy–CLNT composites were compared with theoretical predictions. The relative permittivity of the three-phase composites increased with silver loading. Addition of 0.28 volume fraction of silver increases the relative permittivity of epoxy–CLNT composites from 8 to 142 at 1 MHz. This composite is flexible and can be fabricated into various shapes with low processing temperature.     

Fracture properties of concrete reinforced with steel–polypropylene hybrid fibres

This research discusses polypropylene fibres and three sizes of steel fibres reinforced concrete. The total fibre content ranges from 0% to 0.95% by volume of concrete. A four-point bending test is adopted on the notched prisms with the size of 100×100×500 mm³ to investigate the effect of hybrid fibres on crack arresting. The research results show that there is a positive synergy effect between large steel fibres and polypropylene fibres on the load-bearing capacity and fracture toughness in the small displacement range. But this synergy effect disappears in the large displacement range. The large and strong steel fibre is better than soft polypropylene fibre and small steel fibre in the aspect of energy absorption capacity in the large displacement range. The static service limitation for the hybrid fibres concrete, with “a wide peak” or “multi-peaks” load–CMOD patterns, should be carefully selected. The ultimate load bearing capacity and the crack width or CMOD at this load level should be jointly considered in this case. The K_IC and fracture toughness of proper hybrid fibre system can be higher than that of mono-fibre system.     

Modelling of carbon–carbon composite manufacturing processes

This paper is devoted to the modelling of technological processes of manufacturing of siliconized carbon–carbon composites. The developed model describes the changes that occur in the properties of the composites (strength, elastic moduli, shrinkage) during the technological cycle of manufacturing and also the residual stresses generated in composite structures. It is shown that the level of the residual stresses and the character of changes in the properties of carbon–carbon composites essentially differ from those of polymer–matrix composites.     

Fatigue behaviour of composite–composite joints reinforced with cold metal transfer welded pins

In this paper the fatigue properties of through-the-thickness reinforced joints are studied in detail. Unreinforced specimens, specimens reinforced with cold metal transfer welded titanium and steel pins and specimens reinforced with titanium z-pins are investigated. Besides classical S–N diagrams, hysteresis curves and stiffness based approaches are applied to improve the understanding of the mechanical behaviour of the joints in the progress of their fatigue life. Furthermore full field strain analysis gives information about damage initiation and growth in the joint section.