Volume 31, Issue 4

Textile scientists make researches for producing new types of fibers as well as modifying the existing fibers to provide new raw materials for technical textile applications. The easiest way of modifying fiber physical properties is to change the cross sectional shape of a synthetic fiber. Also, composite fibers loaded with different kinds of additives attracted the attention of researchers in the last decades for functionalizing fibers. Some other methods like coating, exhausting, padding or other novel methods can be used for the same purpose. But in these methods, the functional effect is generally not durable enough against several times of washing and abrasion. Also, these methods usually require higher consumption of water and heat when compared to composite fiber production. As a result, in this work the effect of cross sectional modification and composite fiber production were combined in the same fiber. One of the most important functional properties which can be provided by composite fiber production is antibacterial activity. Only a few research papers were published on antibacterial additive doped polypropylene fibers. In this work cupric oxide (CuO) doped antibacterial composite polypropylene (PP) fibers having different cross sectional shapes (circular, trilobal and triangular) were produced and the effect of cross sectional shape and CuO on the antibacterial activity, structural and mechanical properties of the fibers were investigated for the first time. Cross sectional and longitudinal images of composite fibers were evaluated by using optical microscope and scanning electron microscope (SEM). As the released content of active agent is an important parameter for the activity, durability, environmental and health effect of the product, the copper release from the fibers into the water media was investigated by inductively coupled plasma optical emission spectrometry (ICP-OES). Thermal analysis results showed that PP/CuO composite filaments having three different cross sectional shapes can be produced without any significant changes on thermal behavior of fibers. With the increasing content of cupric oxide, tenacities of fibers slightly decreased. Cupric oxide particles also led to some crystallinity changes. All of the composite fibers showed good antibacterial activity against Gram-negative bacterium Escherichia coli.

The aim of this study was to reveal effects of accelerated weathering in neat polylactide (PLA) and its biocomposite reinforced with microcrystalline cellulose (MCC); compounded by twin-screw extrusion melt mixing and specimen shaping by injection molding. Weathering conditions were applied via consecutive steps of UV irradiation and humidity in accordance with ISO 4892–3 standards for 200 h. Various characterization techniques and mechanical tests indicated that photolysis, photo-oxidation and hydrolysis were the main degradation mechanisms leading to significant decrease in the molecular weight of PLA via main chain scission. Consequently, except elastic modulus other mechanical properties; strength, ductility and fracture toughness of PLA and PLA/MCC decreased substantially. However, after comparing the mechanical properties of the neat PLA and PLA/MCC biocomposite specimens having 200 h of accelerated weathering, it was concluded that; for the outdoor applications use of PLA/MCC biocomposite (with only 3 wt% MCC) was extremely beneficial compared to using neat PLA. For example, tensile strength is more than 91 % beneficial while strain at break ductility is more than 2.7 times beneficial.

This study explores new applications for wood fibres through their incorporation on plastic matrices, developing high performance compounds for the automotive interior. Different automotive grades of polypropylene were reinforced with pine and eucalyptus fibres, in order to compare their properties with the specifications of different vehicle parts. The composites were produced using conventional plastics processing technologies, namely compounding with twin-screw extruder and injection molding. Mechanical properties, density, heat deflection temperature and Vicat softening point were determined. Other specific tests were carried to understand the feasibility of these composites use in automotive parts, namely fogging and flammability and also the determination of the tensile properties after climatic aging tests. The fibres morphology and its distribution and dispersion in the polymer matrices were evaluated by optical and scanning electron microscopy. The results show that it is possible to reinforce the raw-materials using wood and achieve the high standards of the automotive industry, producing environmentally friendlier materials, through the effective reduction of the use of plastic. This work enabled important conclusions regarding the incorporation of wood into PP matrices without compromising the specifications of certain dashboard parts and it also allowed evaluating the processability of these composites.

Peroxide-mediated reactive extrusion of linear isotactic polypropylene (L-PP) was conducted in the presence of trimethylolpropane trimethacrylate (TMPTMA) and triallyl trimesate (TAM) coagents, using a twin screw extruder. The resulting coagent-modified polypropylenes (CM-PP) had higher viscosities and elasticities, as well as increased crystallization temperature compared to PP reacted only with peroxide (DCP-PP). Additionally, deviations from terminal flow, and strain hardening were observed in PP modified with TAM, signifying the presence of long chain branching (LCB). The CM-PP formulations retained the modulus and tensile strength of the parent L-PP, in spite of their lower molar mass and viscosities, whereas their elongation at break and the impact strength were better. This was attributed to the finer spherulitic structure of these materials, and to the disappearance of the skin-core layer in the injection molded specimens.

Thanks to the single stage injection blow molding process, specific hollow parts can be produced with standard injection molding machine. A specific mold is designed, enabling the preform injection molding, as well as its blow molding on the same machine. The preform is blow molded right after its injection molding. This particular process does not involve preform storage and reheating before the blow molding stage. This implies that the preform has to remain sufficiently malleable to be blown while being viscous enough to avoid being pierced during the blow molding stage. The polymer used is a polypropylene random copolymer. Therefore the process takes place between the melting temperature and the crystallization one. As the preform is blow molded right after being injected, this single stage process involves high temperature before the blowing. The polymer rheological behavior is investigated through dynamic rheometry in its molten state at various temperatures. A viscous Cross model is used with the thermal dependence assumed by an Arrhenius law. The process is simulated through a finite element code (Polyflow) in the ANSYS Workbench framework. The geometry allows an axisymmetric approach. The transient simulation is run under anisothermal conditions and viscous heating is taken into account. Two geometries are simulated. First, the flask geometry has been used to show the process efficiency. The yoghurt pot geometry has been designed later for industrial application in a more sophisticated mold than the flask mold. Blow molded parts are analyzed by tomography and the thickness has been measured by the tomography data image analysis. The simulation results are compared to the experimental ones. The simulation fits well with the experimental results concerning both geometries. The simple numerical model proposed proves to be robust enough to predict well the blow molded parts final thickness repartitions provided that the relevant temperature and pressure conditions are well defined.

The aim of this study was to investigate the effects of montmorillonite (MMT) type nanoclay content and maleic anhydride (MA) grafted polylactide (PLA) copolymer compatibilization on the mechanical properties of PLA nanocomposites; compounded by twin-screw extrusion melt-mixing followed with injection molding for shaping of bulk specimens. Successively intercalated and exfoliated structures of the nanocomposites were observed by XRD and TEM analysis, including the chemical interactions by FTIR. Mechanical tests indicated that use of only 1 wt% MMT resulted in significant improvements in many mechanical properties of PLA. Increases were only 14 % in flexural modulus and 7 % in flexural strength, but more than 6 times in ductility and as much as 85 % in fracture toughness values. After MA compatibilization these improvements were much enormous, being more than 22 times in ductility and 119 % in fracture toughness.

In this work, high density polyethylene (HDPE)/hemp fiber composites were produced by extrusion compounding followed by injection molding. In particular, the effect of ground tire rubber (GTR) and coupling agent (maleated polyethylene, MAPE) content was studied to modify the mechanical properties of these natural fiber composites (NFC). From the samples produced, a complete characterization was performed including morphology, density, hardness, as well as mechanical properties in tension, flexion, and impact. The results indicate that substantial improvement in NFC impact strength occurred after GTR addition, while tensile and flexural moduli/strengths decreased. On the other hand, the addition of a coupling agent was able to improve adhesion between each phase resulting in better composite properties. Overall, the final properties of the composites represent a balance between elasticity/toughness from GTR and rigidity/strength from hemp and MAPE. From the data obtained, a regression model for different properties is presented to design/control the final properties of these composites.

Nanocomposites based on high density polyethylene (HDPE)/linear low density polyethylene (LLDPE) blend were prepared by melt compounding in a twin-screw extruder using an organoclay (montmorillonite) as nano-filler and maleic anhydride-grafted linear low density polyethylene (LLDPE-g-MA) as compatibilizer. The effects of two blending protocols were also investigated. In the first blending protocol LLDPE and LLDPE-g-MA were first reinforced with organoclay and then this nanocomposite was later blended with HDPE, and the second blending protocol LLDPE-g-MA was mixed with organoclay first and then this masterbatch was diluted with HDPE and LLDPE. The preparation of the masterbatch resulted in the degradation of polyethylene, with crosslinking formation which increase the viscosity of the polymer and facilitated the dispersion of the organoclay in the polymeric matrix. WAXD and TEM were used to determine the effect of blending protocol and organoclay content on the intercalation and mechanical properties. The introduction of a maleated polyethylene was required to improve the organoclay dispersion in the nanocomposites. Thermal and mechanical properties of the nanocomposites were affected by blending protocols and the content of organoclay. The degree of crystallinity of the materials prepared using the first blending protocol decreased upon the intercalation of clay platelets whereas for the materials obtained using the second blending protocol the degree of crystallinity decreased due the crosslinking which further restricted mobility and diffusion of polymer chains. The nanocomposites show higher values of tensile modulus, flexural modulus and HDT compared to the blend without the addition of organoclay. The OMMT content added to the polymer blend results in significant and well correlated improvements in tensile and flexural moduli.

In this work, the compounds of brominated epoxy resins and antimony trioxide (BER/Sb 2 O 3 ) additives are analyzed and added into long-glass-fiber reinforced polyamide 6 (PA6/LGF) composites in order to solve the “candle-wick effect” caused by glass fibers. The thermal stability, flammability, and morphology of charred residues of the flame retardant PA6/LGF composites are investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), and scanning electronic microscopy (SEM). The results show the addition of BER/Sb 2 O 3 provides improvements in flame retardancy by increasing the LOI values, enhancing UL-94 rating, and reducing the heat release rate, total heat release and effective heat of combustion due to the formation of consolidated and thick charred residual structures on the surfaces of the LGF reinforced PA6 composites. When the content of BER/Sb 2 O 3 is increased to 12 wt%, the LOI value and UL-94 rating of BER/PA6/LGF composites reach 24.8 and V-0, respectively. The TGA results exhibit that the decomposition temperature of the PA6/LGF composites decreases with the addition of BER/Sb 2 O 3 additive, resulting in forming some high quality residual char layer. A possible flame retardant mechanism is proposed to illustrate the effect of the gaseous and condensed phases on the flame retardancy of the PA6/LGF composites.

The demand for the machining and cutting of plastic parts is in continuous increase. The present study is intended to investigate the optimization of high density polyethylene (HDPE-100) orthogonal turning operation using the Grey Relational Analysis (GRA). Accordingly, experimental tests based on Taguchi method are performed to establish a correlation between cutting parameters on one hand and machining force, specific cutting force and roughness of machined surface on the other hand. An optimal parameters combination for the turning process is obtained. In addition to regression models deduction, the analysis of variance (ANOVA) is applied to identify the most significant factors. It is found that the order of the importance of controllable factors to the tangential cutting force (Ft) is feed rate (f), depth of cut (ap) and cutting speed (Vc). However, when considering the importance with respect to specific cutting force (Ks), the order becomes (Vc), (ap) and (f). Finally, the order of cutting parameters according to mean roughness criteria, represented by (Ra), (Rz) and (Rt), shifts to (f), (Vc) and (ap). The optimized cutting regime ensuring minimization of roughness and cutting forces is well described by Vc = 188 m/min, f = 0.14 mm/rev and ap = 3 mm. This study unveiled new approaches based on combined GRA and ANOVA for machining other polymers such as tough reinforced polymers and composites used as human prosthesis.

In this study the electrospinning of polyvinyl alcohol (PVA) was evaluated and optimized for minimum fiber diameter following Taguchi methodology. The effect of four factors including the solution concentration, voltage, flow rate and needle-collector distance each at 3 levels on fiber diameter were investigated. The morphology and the diameter of the fibers were studied by a scanning electron microscope. It was found out from the main effects and the analysis of variance that in the range of levels studied concentration is the most influencing factor on the fiber diameter with a contribution of 89.22 %. Voltage makes a minor contribution of 10.028 % and the flow rate and distance have negligible influence (less than < 1 %). The minimum fiber diameter was predicted to be 381 nm and to be achieved at the combination of concentration of 8 wt.% PVA, voltage of 18 kV, flow rate of 0.7 cm 3 /h and the distance of 10 cm. Validation experiment resulted in fibers with 390 nm diameter which is in close agreement with the predicted value by the Taguchi technique.

We prepared polypropylene/organoclay nanocomposites by melt blending in a twin-screw extruder, exploring the domain of high screw speeds (up to 1 100 min −1 ). The samples were characterized at both microscale (size of agglomerates) and nanoscale (level of exfoliation). We show that, despite a satisfactory exfoliation, the polymer matrix suffered important thermomechanical degradation by chain scission. We propose a way to correct this degradation on the viscosity curves and we confirm that high screw speeds are not necessarily favorable to clay exfoliation, essentially because of the too high melt temperatures encountered during the process.

When working with polymeric compounds containing metallic particles, it is essential to know the influence of the shear rate of different screw elements in a co-rotating twin-screw extruder (TSE) on particle size distribution and particle shape. Particle size and form are significant for various processing conditions. A large variety of TSE screw and mixing elements and a wide range of complex mixing geometries are available for processing polymeric compounds with metallic pigments. In this case study, we investigated the feasibility of extruding powder coatings containing metallic pigments as a replacement for the conventional bonding process. Further, we examined the influence of different screw elements on particle size by means of optical microscopy, scanning electron microscopy, dielectric analysis and terahertz spectroscopy.