T. Boronat

Mechanical and Thermal Properties of Polyvinyl Chloride Plasticized with Natural Fatty Acid Esters

From an industrial point of view, the use of new nontoxic and biodegradable plasticizers coming from natural resources is an interesting alternative to traditional plasticizers based on phthalates. In this study, two types of epoxidized fatty acids esters (EFAE) with different molecular weights have been used in order to produce flexible PVC with low toxicity. Different amounts of EFAE 201 and 401 have been considered in this study. Mechanical and thermal properties have been determined and morphology of fracture surface has been studied by scanning electron microscopy.

Surface modification of polypropylene substrates by UV photografting of methyl methacrylate (MMA) for improved surface wettability

Despite polypropylene is one of the most used commodity plastics, its adhesion properties are remarkably restricted by its non-polar nature which leads to low wetting properties and, consequently, poor adhesion behavior. We report the use of ultraviolet photografting process of methyl methacrylate (MMA) monomer as an efficient chemical treatment for surface activation of polypropylene. Contact angle measurements are used for evaluating changes in polypropylene wetting properties together with surface free energy calculations. Chemical changes are showed in terms of the exposure time to UV radiation. Scanning electron microscopy has been used to evaluate topography changes in a qualitative way; atomic force microscopy has been used for a quantitative evaluation of surface changes in terms of roughness. The use of Fourier transformed infrared spectroscopy has revealed the nature of the chemical changes induced by the photografting process of MMA.

Optimization of atmospheric plasma treatment of LDPE films: influence on adhesive properties and ageing behavior

One of the major disadvantages of low density polyethylene (LDPE) films is their poor adhesive properties. Therefore, LDPE films have been treated with atmospheric pressure air plasma in order to improve their surface properties. So as to simulate the possible conditions in an industrial process, the samples have been treated with two different sample distances (6 and 10 mm), and treatment rates between 100 and 1000 mm s−1. The different sample distances are the distance of the sample from the plasma source. The variation of the surface properties and adhesion characteristics of the films were investigated for different aging times after plasma exposure (up to 21 days) using contact angle measurement, atomic force microscopy, weight loss measurements and shear test. Results show that the treatment increases the polar component () and these changes improve adhesive properties of the material. After the twenty-first day, the ageing process causes a decrease of wettability and adhesive properties of the LDPE films (up to 60%).

The use of wet-laid techniques to obtain flax nonwovens with different thermoplastic binding fibers for technical insulation applications

In this work, the wet-laid technique has been used to obtain flax nonwovens thermally bonded with different contents of polyvinyl alcohol (PVA) and bicomponent polyamide 6/copolyamide (PA6/CoPA) fibers in the 10–30 wt.% range. Scanning electron microscopy has been used to evaluate the formation of interlock points through melted polymer and flax fibers. Volume porosity has been estimated through determination of thickness and surface mass. Tensile strength and elongation at break have been determined on longitudinal (preferential) and transversal directions to evaluate anisotropy. The sound absorption properties of stacked sheets of flax: PVA and flax: PA6/CoPA nonwovens have been evaluated. In addition, the thermal insulating properties of individual nonwovens have been obtained. Mechanical characterization shows slight anisotropy. The absorption coefficient is interesting in the medium frequencies range, and relatively low thermal conductivity and thermal resistance values are obtained with these nonwovens (in the 0.020–0.025 W m−1 K−1 range for flax: PVA nonwovens and in the 0.09–0.10 W m−1 K−1 range for flax: PA6/CoPA nonwovens). By taking into account these features, these nonwoven substrates could find interesting applications as sound absorbers and/or thermal insulation materials in technical applications.

High renewable content sandwich structures based on flax-basalt hybrids and biobased epoxy polymers

In the last years, a growing interest in the development of high environmental efficiency materials has been detected and this situation is more accentuated in the field of polymers and polymer composites. In this work, green composite sandwich structures with high renewable content have been developed with core cork materials. The base resin for composites was a biobased epoxy resin derived from epoxidized vegetable oils. Hybrid basalt-flax fabrics have been used as reinforcements for composites and the influence of the stacking sequence has been evaluated in order to optimize the appropriate laminate structure for the sandwich bases. Core cork materials with different thickness have been used to evaluate performance of sandwich structures thus leading to high renewable content composite sandwich structures. Results show that position of basalt fabrics plays a key role in flexural fracture of sandwich structures due to differences in stiffness between flax and basalt fibers.

Manufacturing and Characterization of Toughened Poly(lactic acid) (PLA) Formulations by Ternary Blends with Biopolyesters

Ternary blends with a constant poly(lactic acid) (PLA) content (60 wt %) and varying amounts of poly(3-hydroxybutyrate) (PHB) and poly(ε-caprolactone) (PCL) were manufactured by one step melt blending process followed by injection moulding, with the main aim of improving the low intrinsic toughness of PLA. Mechanical properties were obtained from tensile and Charpy impact tests. The miscibility and morphology of the system was studied by thermal analysis and field emission scanning electron microscopy (FESEM). The obtained results showed a clear phase separation, thus indicating poor miscibility between these three biopolyesters, i.e., PLA, the continuous component with dispersed PHB and PCL domains in the form of different sphere size. Nevertheless, the high fragility of PLA was remarkably reduced, as detected by the Charpy impact test. In accordance with the decrease in brittleness, a remarkable increase in elongation at break is achieved, with increasing PCL load due to its flexibility; in addition, increasing PCL load provides thermal stability at high temperatures. Thus, tailored materials can be manufactured by melt blending PLA, PHB, and PCL in different percentages to offer a wide range of biodegradable polymer blends.

Validation of the Use of SEBS Blends as a Substitute for Liquid Silicone Rubber in Injection Processes

Liquid silicone rubber is an interesting material at an industrial level, but there are great difficulties in the design and machining of molds, and in addition, it cannot be processed using conventional equipment. Therefore, new lines of research have focused on the search for new materials capable of providing final properties similar to liquid silicone rubber, that can also be engineered using simple, conventional processes and machinery. In this investigation, a range of compatible blends, based on two commercial grades of styrene-b-ethylene-co-butylene-b-styrene (SEBS) thermoplastic elastomer, was studied in order to obtain a range of different Shore A hardness blends for industrial applications where liquid silicone rubber (different hardness) is currently used. The two blended elastomers used had widely differing Shore A hardness values (5 and 90). Once the blended materials had been characterized, the Cross and Williams et al. [20] (Cross-WLF) mathematical model was applied in order to obtain theoretical performance curves for the viscosity of each of the blends. After this, a model was developed using the Computer Aided Engineering (CAE) software package Autodesk Moldflow 2012™. This computer modeling validated the results obtained from the mathematical models, thus making available to process engineers the full range of hardnesses necessary for industrial products (where liquid silicone rubber is used), while still providing the advantages of thermoplastic injection molding.

Mechanical and morphological characterization of novel vinyl plastisols with epoxidized linseed oil as natural‐based plasticizer

Poly(vinyl chloride) (PVC) is one of the most commonly used plastics in the current market due to its low cost and versatility in processing, combined with its satisfactory physical and chemical properties. However, there is an important problem associated to the use of plasticized PVC. This problem is regarding to the toxicity of the most common plasticized used like DOP, DEHP, DINP, due to its possible migration. This problem limits the use of the plasticized PVC in the industry. In this work we have used epoxidized linseed oil (ELO) as a non toxic plasticizer for PVC. This type of natural oil is characterized by acting as both plasticizer and stabilizer of PVC. With this purpose, ELO have been added to PVC. The processing conditions (temperature and time of curing) are vital to determine the final properties of the material. A study of the processing conditions shows the adequate temperature and time to achieve the optimum properties.

Processing and Characterization of Environmentally Friendly Composites from Biobased Polyethylene and Natural Fillers from Thyme Herbs

The main aim of this research work is to assess the potential of a distillery waste from thyme as multifunctional filler in natural fiber reinforced plastics (NFRP) with biobased polyethylene matrix. Several ethylene-based copolymers with different co-monomers (vinyl alcohol, methyl methacrylate, glycidyl methacrylate and acrylic acid) were used as compatibilizer agents to overcome the lack of compatibility between the highly hydrophobic matrix and the highly hydrophilic lignocellulosic filler. The effect of the compatibilizer type and amount, as well as the lignocellulosic filler content was followed by thermal, mechanical, morphological and rheological characterizations. In addition to the typical filler effect, thyme also provides a remarkable increase in thermal stability at moderate temperatures with a positive effect on widening the processing window. The compatibilizer agent that offers best balanced properties is the glycidyl methacrylate copolymer with a noticeable increase in stiffness, flexural and tensile strength. Regarding processability, the viscosity increases with the filler content. This is highly important at low shear rates but the effect is almost negligible at high shear rates typical of injection molding processes.

Disintegration in Compost Conditions and Water Uptake of Green Composites from Poly(Lactic Acid) and Hazelnut Shell Flour

Green composites of poly(lactic acid)-PLA and hazelnut shell flour (HSF) with and without epoxidized linseed oil (ELO) as plasticizer/compatibilizer were subjected to different aging conditions such as water uptake by immersion and disintegration in compost soil. The effect of the hydrolytic degradation was analyzed by measuring the weight gain as a function of the immersion time in water and calculating the corresponding diffusion coefficients. As expected, the water diffusion coefficient increases with HSF content while no remarkable change is obtained for plasticized compositions with ELO. Differential scanning calorimetry reveals a noticeable increase in crystallinity after the degradation process by water immersion. Degradation in controlled compost soil was followed thorough measurements of weight changes. In general, the weight change for a particular degradation time is lower as the HSF content increases. In addition, presence of ELO as plasticizer/compatibilizer delays the degradation process in compost soil. Scanning electron microscopy highlighted a noticeable deterioration of aged samples after 2 weeks with multiple crack formation and high surface abrasion due to microbial activity after 4 weeks.