Thermosetting (bio)materials derived from renewable resources: A critical review

Epoxy resins have been used as structural materials since the late 1940s. Despite their desirable properties such as high strength, excellent creep resistance, and good adhesion, they suffer from low fracture energy. Rubber modification as a major toughening approach to overcome the inherent brittleness of epoxy polymers was introduced during the early 1970s. Since then, a large number of investigations have been conducted to elucidate different aspects of rubber-toughened epoxies. The present work is a critical review of the field focusing on the important parameters affecting rubber-toughening. The studies reviewed are classified in five categories including roles of matrix ductility, rubber concentration, blend morphology, particle cavitation, and particle/matrix interface. It has been tried to provide an in-depth view of the state-of-the-art knowledge in the field and to direct future studies towards exploring new approaches for toughening of epoxy polymers.

Rubber-Toughened Epoxies: A Critical Review

Modification of epoxy resins with functional silanes, polysiloxanes, silsesquioxanes, silica and silicates

Toughening of photo-curable polymer networks: a review

In this study, a high-intensity ultrasonic liquid processor was used to obtain a homogeneous mixture of epoxy resin and multi-walled carbon nanotubes (CNTs). The CNTs were infused into epon 862 epoxy resin through sonic cavitation and then mixed with W curing agent using a high-speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. Flexural tests and fracture toughness tests were performed on unfilled and CNT-filled epoxy to identify the effect of adding CNTs on the mechanical properties of epoxy. The highest improvement in strength and fracture toughness was obtained with 0.3 wt% CNT loading. The nanophased matrix filled with 0.3 wt% CNT was then used with weave carbon fabric in a vacuum-assisted resin transfer molding (VARTM) set up to fabricate composite panels. Flexural tests, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA) were performed to evaluate the effectiveness of adding CNTs on the mechanical and thermal properties of the composite. The glass transition temperature, decomposition temperature, and flexural strengths were improved by infusing CNTs. Based on the experimental result, a linear damage model has been combined with the Weibull distribution function to establish a constitutive equation for neat and nanophased carbon/epoxy. Simulated result show that that infusing CNTs increases Weiubll scale parameter, but decrease Weibull shape parameter.

Fabrication and characterization of carbon/epoxy composites mixed with multi-walled carbon nanotubes

Modification of epoxy resin using reactive liquid (ATBN) rubber

Epoxy resins are widely used as high-performance thermosetting resins for many industrial applications, but unfortunately, some are characterized by a relatively low toughness. In this respect, many efforts have been made to improve the toughness of cured epoxy resins by the introduction of rigid particles, reactive rubbers, interpenetrating polymer networks, and thermoplastics within the matrix. In this work, kaolin as a modifier was added at different contents to improve the toughness of diglycidyl ether of bisphenol A epoxy resin with polyamino-imidazoline as a curing agent. The chemical reactions suspected of taking place during the modification of the epoxy resin were monitored and evaluated with Fourier transform infrared spectroscopy. The glass-transition temperature (Tg) was measured with differential scanning calorimetry. The mechanical behavior of the modified epoxy resin was evaluated in terms of the Izod impact strength (IS), the critical stress intensity factor (KIC), and tensile properties at different modifier contents. Scanning electron microscopy (SEM) was used to elucidate the mechanisms of deformation and toughening in addition to other morphological features. Finally, the adhesive properties of the modified epoxy resin were measured in terms of tensile shear strength (TSS). With the addition of kaolin, the reactivity test revealed that the gel time and temperature, exotherm peak, and cure time were reduced. Infrared spectra showed the existence of a chemical reaction between kaolin and the epoxy resin. The presence of kaolin caused a steady decrease in Tg by about 10°C until 15-phr kaolin was reached prior to leveling off. Most of the tensile properties attained a peak at an approximately 10-phr kaolin content where the toughening reached its maximum. The modulus increased linearly from 1.85 to 2.7 GPa with increasing kaolin content. For both notched and unnotched specimens, a twofold increase in Izod IS was obtained by the addition of just 10-phr kaolin compared to the unfilled resin. On the addition of kaolin, the Izod IS varied from 0.85 to 1.53 kJ/m2 for notched specimens and from 4.19 to 8.32 kJ/m2 for unnotched specimens, whereas KIC varied from 0.91 to 2.63 MPa m1/2 with increasing kaolin content. The adhesive properties, evaluated in terms of TSS, increased from 9.14 to 15.02 MPa. SEM analysis revealed that the prevailing toughening mechanism for the epoxy resin under consideration was localized plastic shear yielding induced by the presence of kaolin particles associated with crack pinning. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 861–878, 2001

Modification of epoxy resin with kaolin as a toughening agent

This paper presents an attempt to improve the properties of poly(3-hydroxybutyrate) (P3HB) using linear aliphatic polyurethane (PU400) and organomodified montmorillonite (MMT)—(Cloisite®30B). The nanostructure of hybrid nanobiocomposites produced by extrusion was analyzed by X-ray diffraction and transmission electron microscopy, and the morphology was analyzed by scanning electron microscopy. In addition, selected mechanical properties and thermal properties were studied by thermogravimetric analysis, TGA, and differential scanning calorimetry, DSC. The interactions of the composite ingredients were indicated by FT IR spectroscopy. The effect of the amount of nanofiller on the properties of prepared hybrid nanobiocomposites was noted. Moreover, the non-equilibrium and equilibrium thermal parameters of nanobiocomposites were established based on their thermal history. Based on equilibrium parameters (i.e., the heat of fusion for the fully crystalline materials and the change in the heat capacity at the glass transition temperature for the fully amorphous nanobiocomposites), the degree of crystallinity and the mobile and rigid amorphous fractions were estimated. The addition of Cloisite®30B and aliphatic polyurethane to the P3HB matrix caused a decrease in the degree of crystallinity in reference to the unfilled P3HB. Simultaneously, an increase in the amorphous phase contents was noted. A rigid amorphous fraction was also denoted. Thermogravimetric analysis of the nanocomposites was also carried out and showed that the thermal stability of all nanocomposites was higher than that of the unfilled P3HB. An additional 1% mass of nanofiller increased the degradation temperature of the nanocomposites by about 30 °C in reference to the unfilled P3HB. Moreover, it was found that obtained hybrid nanobiocomposites containing 10 wt.% of aliphatic polyurethane (PU400) and the smallest amount of nanofiller (1 wt.% of Cloisite®30B) showed the best mechanical properties. We observed a desirable decrease in hardness of 15%, an increase in the relative strain at break of 60% and in the impact strength of 15% of the newly prepared nanobiocomposites with respect to the unfiled P3HB. The produced hybrid nanobiocomposites combined the best features induced by the plasticizing effect of polyurethane and the formation of P3HB–montmorillonite–polyurethane (P3HB-PU-MMT) adducts, which resulted in the improvement of the thermal and mechanical properties.

https://www.mdpi.com/2079-4991/13/2/225/pdf?version=1672839931

Polymer/Layered Clay/Polyurethane Nanocomposites: P3HB Hybrid Nanobiocomposites—Preparation and Properties Evaluation

This article presents a review on the recent advances in the field of ternary diglycidyl ether of bisphenol A epoxy nanocomposites containing nanoparticles and other modifiers. Particular attention is paid to their mechanical and thermal properties. The properties of epoxy resins were improved by incorporating various single toughening agents, in solid or liquid states. This latter process often resulted in the improvement in some properties at the expense of others. The use of two appropriate modifiers for the preparation of hybrid composites, possibly will show a synergistic effect on the performance properties of the composites. Due to the huge amount of modifiers that were used, the present paper will focus mainly on largely employed nanoclays with modifiers in a liquid and solid state. The former modifier contributes to an increase in the flexibility of the matrix, while the latter modifier is intended to improve other properties of the polymer depending on its structure. Various studies which were carried out on hybrid epoxy nanocomposites confirmed the occurrence of a synergistic effect within the tested performance properties of the epoxy matrix. Nevertheless, there are still ongoing research works using other nanoparticles and other modifiers aiming at enhancing the mechanical and thermal properties of epoxy resins. Despite numerous studies carried out so far to assess the fracture toughness of epoxy hybrid nanocomposites, some problems still remain unresolved. Many research groups are dealing with many aspects of the subject, namely the choice of modifiers and preparation methods, while taking into account the protection of the environment and the use of components from natural resources.

/pdf/hybrid-epoxy-nanocomposites-improvement-in-mechanical-nelua4mo.pdf

Hybrid Epoxy Nanocomposites: Improvement in Mechanical Properties and Toughening Mechanisms—A Review

Poly(3-hydroxybutyrate) (P3HB) is the most important of the polyhydroxyalkanoates. It is biosynthesized, biodegradable, biocompatible, and shows no cytotoxicity and mutagenicity. P3HB is a natural metabolite in the human body and, therefore, it could replace the synthetic, hard-to-degrade polymers used in the production of implants. However, P3HB is a brittle material with limited thermal stability. Therefore, in order to improve its mechanical properties and processing parameters by separating its melting point and degradation temperature, P3HB-based composites can be produced using, for example, linear aliphatic polyurethanes as modifiers. The aim of the study is a modification of P3HB properties with the use of linear aliphatic polyurethanes synthesized in reaction of hexamethylene diisocyanate (HDI) and polypropylene glycols (PPG) by producing their composites. Prepared biocomposites were tested by the scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry (TGA). Furthermore, selected mechanical properties were evaluated. It has been confirmed that new biocomposites showed an increase in impact strength, relative strain at break, decrease of hardness and higher degradation temperature compared to the unfilled P3HB. The biocomposites also showed a decrease in the glass transition temperature and the degree of crystallinity. Biocomposites obtained with 10 wt. % polyurethane synthesized with polypropylene glycol having 1000 g · mole–1 and HDI have the best thermal and mechanical properties.

/pdf/biobased-poly-3-hydroxybutyrate-acid-composites-with-2iqc0kde.pdf

M. Bakar

Papers

Modification of epoxy resin using reactive liquid (ATBN) rubber

Modification of epoxy resin with kaolin as a toughening agent

Polymer/Layered Clay/Polyurethane Nanocomposites: P3HB Hybrid Nanobiocomposites—Preparation and Properties Evaluation

Hybrid Epoxy Nanocomposites: Improvement in Mechanical Properties and Toughening Mechanisms—A Review

Biobased poly(3-hydroxybutyrate acid) composites with addition of aliphatic polyurethane based on polypropylene glycols