Liliana B. Manfredi

Thermal degradation and fire resistance of epoxy-amine-phenolic blends

The effects of the addition of different epoxy resins on the thermal stability of phenolic resolees are reported. Blends of phenolic resins with different compositions of epoxy resins, cured with amine hardeners, were characterized by thermal gravimetric analysis and cone calorimetry to determine their thermal stability and fire resistance. The thermal degradation of phenolic resolees is characterized by a complex mechanism with at least two different processes which lead to the production of a stable and resistant char structure. On the other hand, the epoxy resins studied, either aliphatic or aromatic, degrade in a single step. The results demonstrate that the epoxy–amine content should be kept under 15 wt.% to avoid a significant reduction of the thermal stability of the blend. However, blending with epoxy–amines is a suitable route to improve the mechanical properties of phenolic resins or to reduce the cure temperature.

Development of carbon fiber/phenolic resin prepregs modified with nanoclays

This work is focused on the study of the main variables involved in the development of phenolic/carbon prepregs and how these variables are affected by the incorporation of nanoclays. For this, phenolic resin was obtained from phenol and formaldehyde, performing the reaction under basic conditions and with formaldehyde excess. Resin curing kinetics was studied by means of Fourier transform infrared spectroscopy measurements. Organo-modified clay was added to the phenolic resin in order to evaluate their effect on the general performance of the material. Carbon fiber/phenolic resin and carbon fiber/clay modified phenolic resin prepregs were obtained by hand-layup and vacuum bagging. Prepregs were characterized in terms of fiber content, flexural stiffness, and degree of tack. In both the cases, intermediate fiber volume content, nearly 50%, was obtained. The addition of 5 wt% of clay to the phenolic resin did not produce a significant change on the prepregs stiffness but increased the degree of tack, which implies that the incorporation of such particles was useful to enhance the prepregs properties. Composite materials were obtained by compression molding of the prepregs obtained, and were characterized by its fiber content, mechanical behavior with the three-point bending test and its thermal degradation by thermogravimetry. High fiber content composites materials were obtained, nearly 75% by volume. However, modified composites showed lower fiber content, which resulted in a decrease of the flexural modulus and strength. In relation to thermal degradation, the addition of nanoclay did not change the behavior of the materials.

Influence of Processing Conditions on Morphological, Thermal and Degradative Behavior of Nanocomposites Based on Plasticized Poly(3-hydroxybutyrate) and Organo-Modified Clay

Abstract The effect of processing conditions (casting and extrusion) and plasticization on the disintegrability in compost of organically modified clay poly(3-hydroxybutyrate) nanocomposites was studied. Tributylhexadecylphosphonium bromide (TBHP) was used as organic modifier. As revealed by WAXS and TEM observations, intercalated nanobiocomposites with clay stacks and some individually dispersed platelets were obtained. The melting temperature of the neat PHB diminished with the addition of plasticizer, thus broadening the processing window. Biodegradation test revealed that while the clay slows down the degradation rate, the plasticizer increases the degradation of the samples, reaching a similar final percentage of disintegrability when both plasticizer and clay were added in the formulation.

Effect of Cellulose Nanocrystals and Bacterial Cellulose on Disintegrability in Composting Conditions of Plasticized PHB Nanocomposites

Poly(hydroxybutyrate) (PHB)-based films, reinforced with bacterial cellulose (BC) or cellulose nanocrystals (CNC) and plasticized using a molecular (tributyrin) or a polymeric plasticizer (poly(adipate diethylene)), were produced by solvent casting. Their morphological, thermal, wettability, and chemical properties were investigated. Furthermore, the effect of adding both plasticizers (20 wt % respect to the PHB content) and biobased selected nanofillers added at different contents (2 and 4 wt %) on disintegrability in composting conditions was studied. Results of contact angle measurements and calorimetric analysis validated the observed behavior during composting experiments, indicating how CNC aggregation, due to the hydrophilic nature of the filler, slows down the degradation rate but accelerates it in case of increasing content. In contrast, nanocomposites with BC presented an evolution in composting similar to neat PHB, possibly due to the lower hydrophilic character of this material. The addition of the two plasticizers contributed to a better dispersion of the nanoparticles by increasing the interaction between the cellulosic reinforcements and the matrix, whereas the increased crystallinity of the incubated samples in a second stage in composting provoked a reduction in the disintegration rate.

Fire performance of composites made from carbon/phenolic prepregs with nanoclays

This article describes the development of fire resistant composite materials based on phenolic resin and carbon fibers. Two types of composites were developed, with neat phenolic resin and with phenolic resin/modified bentonite. Composite materials were processed from prepregs by compression molding and were characterized by density, fiber content, cone calorimeter test, scanning electron microscope, and mechanical properties before and after the exposure to fire. In both cases, high fiber content materials were developed, about 75% by volume. The addition of clay improved some fire properties such as the peak of the heat release rate and the residual mass of the burned samples. Also, the bentonite-modified composite required higher time to develop the maximum of the heat release rate in the material; therefore, the addition of modified nanoclays improved the fire properties of the developed composites. Regarding to mechanical behavior the modified composites presented low modulus and flexural stiffness than the unmodified materials, and presented a higher decreased in the properties after fire, which could be related with the different fiber content in both composites.

Study of the ablative properties of phenolic/carbon composites modified with mesoporous silica particles

Mesoporous silica particles and carbon black were selected as fillers for a resol-type phenolic resin, to be used as a matrix for ablative materials. Composites were processed with the modified polymer and carbon fibers were used as continuous reinforcement. The ablative properties of the materials obtained were studied by the oxyacetylene torch test and the ablated samples were observed by scanning electron microscopy. Composites with 30 wt. % of carbon black achieved the lowest linear erosion rate and the highest insulation index, denoting the ability of the char produced to protect the virgin material. Considering that such composite has 44% by volume of carbon fibers, it could be inferred that its properties could be improved by increasing the fiber content and maintaining the amount of carbon black. The composite with 20 wt. % of mesoporous silica particles exhibited the lowest mass erosion rate, indicating a better stabilization of the char. Regarding dynamic-mechanical properties, the addition of particles induced a decrease in the modulus and glass transition temperature of all the systems studied.