Water ageing of SMC composite materials: a tool for material characterisation

Diffusion of electrolytes in hydrolyzable glassy polymers: Acetic acid in poly(vinyl acetate), poly(vinyl alcohol), and polyesters

“…In the case of UPE/PVAc, the methodology of the experiments, on combined sorption of water and desorption of HAc, included the following steps: Sorption experiments were performed isothermally at 70°C in “hydrothermal” conditions (sorption from liquid water)5–7, 12 on films conditioned in an exsiccator under a vacuum to a constant weight ( W i ) at the temperature of the next experiment. Using a Sartorius analytical balance, with a resolution of 0.1 mg, a film was weighed ( W t ) at selected times ( t ) after wiping the drops of water. Then, water was desorbed by heating at the temperature of the corresponding sorption experiment under a vacuum to a constant weight ( W 0 ).…”

“…Then, water was desorbed by heating at the temperature of the corresponding sorption experiment under a vacuum to a constant weight ( W 0 ). The results of the water‐desorption experiments were further treated to calculate the water‐diffusion coefficient corresponding to the time ( t ) of sorption (see below). The weight ( M wt ) of water and its concentration in the material ( C wt : g/g) were calculated from Sorption experiments were completed when C wt became constant, C w ∞ (“equilibrium value”). The water‐diffusion coefficient of specimens undergoing water sorption was calculated from the desorption experiments which were proved5–7, 12 to show Fickian kinetics: where C is the water concentration in the material as it varies with time during the desorption process, and C w 0 , the water concentration in the material prior to desorption: It corresponds to the concentration of water absorbed by the material before desorption begins. The amount of acid ( M st ) leached the material to time t was calculated from Similar to the water case, leaching experiments were completed when M st became a constant equilibrium value, M s ∞ .…”

“…In PVAc‐containing polyester resin–glass fiber composites, these processes are the swelling and partial dissolution of vinyl acetate and vinyl alcohol sequences and unsaturated polyester (UPE) plasticization. Therefore, PVAc hydrolysis, which promotes the softening of the SMC composites and consequent loss of their mechanical properties, may prevent the use of PVAc owing to its effect on the durability in spite of its superior performance in terms of shrinkage control 6, 7…”

Automotive Plastics and Composites

“…In addition, researchers are also investigating natural replacements for SMC filler, calcium carbonate, by incorporating soy, corn, and cellulose fillers into the composites. The use of natural fibers and fillers can pose issues with water absorption and paint surface appearance (27).…”

Estudio de la degradación de materiales compuestos base poliéster reforzados con fibra de vidrio en medios neutros y alcalinos

“…Una vez en el interior, la matriz puede sufrir: hidrólisis de ciertos grupos moleculares de naturaleza ácida o álcali, ampollamiento, plastificación, saponificación, grietas o microgrietas, además de ataque de la interfase fibra-matriz, provocando deterioro en la unión y pérdida de integridad, no recuperando sus características mecánicas originales [Apicella 1983, Chua 1992b, Liao 1998]. El agua puede actuar como agente plastificante, produciendo el hinchamiento de la resina, que genera tensiones internas [Camino 1998] y hace que sus propiedades se vean seriamente afectadas por el fallo de unión en la interfase [Boinard 2000], además de producir reacciones de hidrólisis en la matriz [Schutte 1994], este efecto se acentúa especialmente a altas temperaturas [Miyazaki 1998]. La presencia de agua además hace disminuir la temperatura de transición vítrea y con lo que se reduce el rango de temperaturas de trabajo, debido a la plastificación de la matriz, que permite una mayor movilidad de las cadenas [Marais 1999, Kajorncheappunngam 2002.…”