Enhanced mechanical properties of epoxy composites using cellulose micro- and nano-crystals

Epoxy polymers are commonly utilized in structural applications due to their high bearing capacity and excellent chemical resistance. However, their inherent brittleness poses a significant challenge for their use in high shock and fracture strength products. To address this shortcoming, fillers can be incorporated into the polymer during preparation. In this study, we aimed to investigate the effect of incorporating cellulose-based fillers, namely cellulose nanocrystals (CNCs) and microcrystalline cellulose (MCC), on the mechanical properties of epoxy polymer composites. The study evaluated the impact of various factors, including filler concentration, particle size, and moisture content, on the mechanical properties of the composites. The results demonstrated that the incorporation of CNC or MCC powders at concentrations below 5% could enhance the mechanical properties of the resulting epoxy composites without adversely affecting their surface and thermal properties. The maximum tensile strength and fracture toughness of the filler-based epoxy composites were achieved at 2 and 4 wt% for CNCs and MCC, respectively. CNCs with a smaller particle size distribution were found to be much more effective than MCC in improving the mechanical properties of the epoxy composites. Furthermore, utilizing dried fillers resulted in a higher improvement in tensile strength, which was achieved at lower filler concentrations.     

The effect of hygrothermal fatigue on physical/mechanical properties and morphology of neat epoxy resin and graphite/epoxy composite

The effect of moisture absorption, desorption, and thermal spiking on the physical/mechanical properties of TGDDM/DDS epoxy resin was investigated and compared to the Gr/Ep composite. The mechanism of moisture diffusion in the neat resin was described on the morphological level. The diffusion rate of moisture in epoxy resin was found to depend on the mobility of molecular chains within an inhomogeneous epoxy network. Two well-known concepts of plasticization of amorphous polymers, the lubricity theory and the gel theory, were invoked to describe the interactions between the absorbed moisture and the resin network. Slight permanent changes in properties of the neat resin were observed after one absorption-desorption cycle. In the thermal spiking experiment, only the spiking temperature above the glass transition of the moisture saturated epoxy resins changed their internal structure and produced very small (thin) microcracks. By comparison with the neat epoxy resin, the Gr/Ep composites contain the reinforcement-matrix boundary region, characterized by the highest restrictions to molecular mobility. The absorbed moisture during the static hygrothermal fatigue cannot effectively plasticize this region. But during thermal spiking, the formation of microcracks is observed within the reinforcement-matrix boundary region as well as an increase in the moisture content.     

The effect of epoxy‐polyester hybrid resin on mechanical properties,rheological behavior,and water absorption of polypropylene wood flour composites

The effect of epoxy resin on mechanical and Rheological properties, and moisture absorption of wood flour polypropylene composites (WPCs) were investigated. The reactive mixing of epoxy resin with 30, and 40 wt% wood flour and polypropylene (PP) was carried out in twin screw extruder with a special screw elements arrangement. PP grafted maleic anhydrides (MPP) were used as coupling agent to improve the interfacial interactions of wood flour, epoxy resin, and PP. The tensile strength of composites decreased, and elastic modulus and moisture absorption increased with increasing epoxy resin content. The complex viscosity η* increased with increasing epoxy resin content of composites, and a synergistic effect in increasing the η* was observed at 3 wt% resin. The epoxy resin modified wood‐PP composites that chemically coupled by MPP showed minimum water absorption with highest elastic modulus. The experimental oscillation rheologyical data were used to drive a model to predict the flow behavior of WPCs, in a wide range of frequencies. POLYM. ENG. SCI., 47:2041–2048, 2007. © 2007 Society of Plastics Engineers     

Epoxy and glass composites in water studied with 2H-NMR

The amount, behavior, and localization of water in epoxy resin composites largely influence the mechanical properties and aging. Gravimetric analysis combined with ²H-NMR of heavy water in epoxy resin glass fabric composites provides direct information about types of water, which can be distinguished by their mobility. Three different epoxy composites were analyzed with this technique. The results are correlated with mechanical properties.     

Effect of the water sorption on the mechanical response of microcrystalline cellulose‐based composites for art protection and restoration

Thermoplastic composites based on a commercial acrylic matrix widely used in the field of art protection and restoration (Paraloid B72) and various concentrations (up to 30 wt %) of microcrystalline cellulose powder (MCC) were prepared by melt‐compounding and compression molding. The mechanical behavior of the resulting materials conditioned at a temperature of 23°C and a relative humidity level of 55% was compared to that of the corresponding dried materials. Even though the moisture absorption of the filler was lower than the neat matrix, the maximum moisture content increased with the MCC amount, probably due to the preferential water diffusion path through the microvoids and/or the filler‐matrix interface. Although the increase of moisture content for filled samples, DMTA analysis evidenced a stabilization upon MCC introduction, with an increase of the storage modulus and a decrease of the thermal expansion coefficient proportional to the filler loading. A similar trend was displayed by the corresponding dried materials. The tensile elastic modulus and the ultimate properties such as the stress at break and the tensile energy to break (TEB) of conditioned samples increased proportionally to the filler amount. On the contrary, the failure properties of dried composites were negatively affected by the presence of the microcellulose. It is worthwhile to report that a significant improvement of the creep stability was induced by MCC introduction both for dried and conditioned samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40741.     

Modification of cellulose fibers with functionalized silanes: Effect of the fiber treatment on the mechanical performances of cellulose–thermoset composites

Unsaturated polyester and epoxy resin matrices were filled with silane‐treated cellulose fibers and the ensuing composites were tested in terms of mechanical properties before and after accelerated aging consisting of their immersion into water. The coupling agents used were γ‐aminopropyltriethoxysilane (APS), γ‐methacrylopropyltrimethoxysilane (MPS), hexadecytrimethoxysilane, and γ‐mercaptopropyltrimethoxysilane (MRPS) and those containing reactive functions capable of reacting at one end with the fibers and at the other with the matrix, namely, APS, MPS, and MRPS, were more efficient in improving the mechanical properties of the composites. The immersion into water induced a drastic loss of mechanical properties of the materials. The water uptake of the composites was also studied and showed that the silane treatment was poorly efficient in preventing cellulose from water absorption. The fracture surfaces were inspected by scanning electron microscopy, which confirmed the quality of the interface. These observations were in agreement with the results obtained from the dynamic mechanical characterization. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 974–984, 2005     

Enhancing thermal and dynamic-mechanical properties of epoxy reinforced by amino-functionalized microcrystalline cellulose

In this study, microcrystalline cellulose (MCC) was chemically modified with 3-(aminopropyl)triethoxysilane and added to epoxy to improve chemical, thermal and dynamic-mechanical characteristics of the composites. The composites were manufactured aided by sonication with 1.0%, 2.5%, or 5.0% wt/wt of untreated MCC or amino-functionalized MCC (MCC-Si). The epoxy/MCC-Si composites showed a decrease in the ─OH band by Fourier-transform infrared spectroscopy, and X-ray diffraction analysis indicated better dispersion. The incorporation of MCC-Si in epoxy resin decreased the heat of reaction, increased activation energy values (E_a) and pre-exponential factor (A), and did not affect thermal degradation. All conversion degree (α) versus temperature curves for the composites showed a sigmoidal shape. MCC-Si composites showed better dynamic-mechanical properties than the MCC counterparts, and the functionalization effect was evidenced in storage modulus (E') and loss modulus (E"). At 2.5% wt/wt of MCC-Si content an increase of 119% in E' at the glassy region, 127% in E' at the rubbery region and 173% in E" was observed compared to the neat resin, whereas the T_g barely changed among samples. Good adhesion between the amino-functionalized MCC and the epoxy matrix was observed at the fracture surface, evidencing that surface modification of MCC improves their chemical interaction.     

Preparation and characterization of chemically modified Jute–Coir hybrid fiber reinforced epoxy novolac composites

In this study, the effects of fiber surface modification and hybrid fiber composition on the properties of the composites is presented. Jute fibers are cellulose rich (>65%) modified by alkali treatment, while the lignin rich (>40%) coconut coir fibers consist in creating quinones by oxidation with sodium chlorite in the lignin portions of fiber and react them with furfuryl alcohol (FA) to create a coating around the fiber more compatible with the epoxy resins used to prepare polymer composites. The maximum improvement on the properties was achieved for the hybrid composite containing the jute–coir content of 50 : 50. The tensile and flexural strength are recorded as 25 and 63 MPa at modified coir fiber content of 50 vol %, respectively, which are 78% and 61% higher than those obtained for unmodified fiber reinforced composites, i.e., tensile and flexural strength are 14 and 39 MPa, respectively. The reinforcement of the modified fiber was significantly enhanced the thermal stability of the composites. SEM features correlated satisfactorily with the mechanical properties of modified fiber reinforced hybrid composites. SEM analysis and water absorption measurements have confirmed the FA-grafting and shown a better compatibility at the interface between chemically modified fiber bundles and epoxy novolac resin. Hailwood–Horrobin model was used to predict the moisture sorption behavior of the hybrid composite systems. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of moisture absorption on mechanical and viscoelastic properties in liquid thermoplastic resin/carbon fiber composites

This article investigated the effect of moisture on the tensile strength and in‐plane shear of laminated composites. For this, the results of a composite system based on a new thermoplastic Elium® 150 resin were compared to a traditional epoxy resin result. Both composites were fabricated via VARTM using a 0/90° plain weave carbon fiber fabric. For the non‐conditioned specimens, the thermoplastic composites presented 30% more tensile resistance in comparison to epoxy composites. For conditioned specimens, this difference was 14%. These results were related to plasticization, which tends to favor the polymer softening providing a greater matrix plastic deformation, promoting a ductile fracture of the composite. On the other hand, the in‐plane shear properties were 30% higher for the thermosetting laminates for both conditions. In this case, moisture may have favored the formation of surface cracks and weakened the fiber/matrix interfacial adhesion. Additional analysis based on design of experiments has shown that the Elium® 150 resin significantly affects all responses and presented in fact a better behavior in comparison to Epoxy resin. While the conditioning effects have featured a statistically noticeable contribution to the tensile strength, the presence of the moisture did not provide a significant enhancement to the in‐plane shear strength. Besides that, the unknown fractographic aspects of the fracture surfaces of both composites were used as a complementary tool for the mechanical characterization. POLYM. ENG. SCI., 59:2185–2194, 2019. © 2019 Society of Plastics Engineers     

Physico‐mechanical,thermal, and coating properties of composite materials prepared with epoxy resin/steel slag

The interest in using different solid waste as reinforcement in polymer composite preparation has increased considerably in recent years. Slag is one of the inorganic waste materials obtained from ore processing. In this work, epoxy composites filled with different percentages of slag were prepared. Physico‐mechanical, thermal, and coating properties of these composites were determined depending on the amount of filler, type of hardener, and polyethylene glycol (PEG) addition. X‐ray diffraction (XRD) studies were carried out to examine the compatibility of the filler and epoxy resin and XRD results showed good compatibility between two materials. The results of mechanical testing illustrated that hardness of the epoxy composites containing anhydride was partially higher than with Epamine PC17 in contrast to elongation at break. The tensile strength and Young modulus decreased with increasing filler amount. When compared to neat epoxy resin, corrosion, and adhesion properties of the composites with filler addition did not change significantly. The highest water sorption values were obtained for the epoxy composites with PEG addition. The composites hardened by anhydride had better thermal stability than the composites including Epamine PC17. POLYM. COMPOS., 38:1974–1981, 2017. © 2015 Society of Plastics Engineers     

Interactions of Kevlar® fibers with selected model compounds: water sorption and dynamic mechanical properties of fiber/matrix samples

The present study deals with the sorption of water on Kevlar®? fibers and on a selected range of fiber-reinforced samples, in order to characterize the related interactions and to determine their influence on the dynamic properties (tan δ) of the specimens tested. The diffusion coefficients and the water content values at equilibrium show that the fibers significantly 'slow down' the diffusion with respect to the matrix. Water regain is proportional to the capacity of each component to sorb water. The rheological behavior of the composites reveals a plasticization effect associated with the water sorption. This phenomenon can be masked under certain experimental conditions. Among the treatments performed on the Kevlar® fibers to enhance the adhesion to the matrix, an epoxy coating tends to reduce the water regain, the rate of sorption, and the plasticization effects, while the plasma treatment did not reveal a significant effect in this study.     

Evaluation of structural changes in epoxy systems by moisture sorption-desorption and dynamic mechanical studies

This work forms a basis for relating moisture solubilities and dynamic mechanical properties to the hygrothermal history of epoxy systems. Two different classes of epoxy systems were investigated; a low-performance epoxy (DGEBA-TETA) and a high-performance system (TGDDM-DDS) commonly used in carbon fiber composites. An increase in the equilibrium moisture content from TGDDM-DDS epoxy samples having various DDS compositions was observed as a result of thermal cycling in a liquid environment. Interpretation of the experimental results suggest that hygrothermal interactions produce changes in the epoxy network structure and result in the observed moisture sorption behavior.     

One-step synthesis of improved silica/epoxy nanocomposites with inorganic-organic hybrid network

High performance silica/epoxy nanocomposites were prepared through mixing epoxy, tetraethyl orthosilicate (TEOS), γ-aminoproplytriethyoxy siliane(APTES), and triethyltrtramine (TETA) at 25 °C via sol-gel method on one-step. The effects of content of TEOS and coupling reagents on the mechanical and thermal properties of SiO₂/EP composites were studied. Microcosmic morphology and properties of the hybrid materials were characterized by FT-IR, TEM, FESEM, and DSC. Results revealed that SiO₂/EP composites achieve the optimal mechanical and thermal properties when the composites prepared with mass ratio of TEOS/APTES/epoxy for 3/2/100 without acetone. Compared with pristine epoxy, the tensile strength, elongation at break, impact strength and bend strength increased 67.6 %, 190 %, 82.1 % and 15.7 %, respectively. The further study was to investigate the content of TEOS and APTES effecting on mechanical properties and water sorption of fiber reinforced composites, which used the above compound as matrix resin.     

树脂基玻璃纤维复合材料吸湿对性能影响及其机理研究

研究了树脂基玻璃纤维增强复合材料吸湿过程及其机理。通过对玻璃纤维复合材料吸湿后相关性能的测试,了解了复合材料的吸湿行为,以及吸湿行为对相关性能的影响。研究认为树脂基体及界面的吸湿行为对材料整体性能影响很大,宏观表现为力学性能、热性能等明显下降。研究结果表明纤维复合材料吸湿性不仅取决于树脂基体,与纤维及界面均有关系。     

Moisture effects on FM300 structural film adhesive: Stress relaxation,fracture toughness,and dynamic mechanical analysis

The behavior of cured FM300 epoxy, a structural film adhesive, subjected to partial and full moisture saturation has been evaluated. Three separate but interrelated test methods were used: stress relaxation, fracture toughness, and dynamic mechanical testing. The mechanical response of the epoxy due to increasing moisture content was dependent on the testing method. In stress relaxation testing, the epoxy was plasticized when partially saturated with moisture, but it became more rigid when fully saturated. The plasticization‐to‐stiffening transition was not observed in the other two test methods. Fracture testing showed that the material toughness increased with increasing moisture concentration: plasticization effects were dominant. Similar changes in the loss modulus were found in dynamic mechanical analysis. We propose that the differences in behavior have been due to differences in load levels and loading rates used in these probing techniques. Stress relaxation testing, at a relatively lower load and loading rate, appeared to be more sensitive to the localized interactions between the absorbed water molecules and the crosslinked structure. Higher loads and loading rates tended to reveal the bulk effects of plasticization only. Nevertheless, there was also strong evidence from glass‐transition temperature measurements that these moisture effects were mostly reversible. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95:1285–1294, 2005     

Durability of Aluminium Adhesive Joints Bonded with a Homopolymerised Epoxy Resin

The durability of epoxy-aluminium joints that use a homopolymerised epoxy resin was studied, and the effects of relative humidity, temperature, and salt concentration were analysed. The adhesive properties were measured by lap-shear tests, and the water uptake of the epoxy resin was determined by gravimetric measurements. Ageing and degradation effects on the epoxy resin and on the aluminium substrates were also analysed.

The homopolymerised epoxy resin absorbs little water (1.5 wt%) because of its nonpolar network structure. The water uptake is enhanced by increasing relative humidity and temperature; however, the joint strength remains constant because of epoxy plasticization. A saline environment is damaging to the adhesive joints, because of metal corrosion, but was not significantly harmful to the epoxy resin, because of a lower diffusion coefficient of salt water. The T_g decrease of the epoxy adhesive due to water absorption depends only on the amount of absorbed water and is independent of the hydrothermal ageing conditions.     

Effect of water sorption on the structure and mechanical properties of an epoxy resin system

The characteristics of sorption and diffusion of water in an amine‐cured epoxy system based on tetraglycidyl diaminodiphenylmethane and a novolac glycidyl ether resin were studied as a function both of the polymer microstructure, known from previous works, and the temperature. Water‐sorption experiments and dynamic mechanical analysis (DMA) were performed. Tensile stress–strain and Rockwell hardness tests were conducted to investigate the effects of absorbed water on the mechanical properties of the material. Competing effects of the sorption of water in the free volume and of strong interactions between water molecules and polar groups of the network were used to explain the diffusional behavior observed, which followed Fick's second law. DMA analysis seemed to be sensitive to the water effects and the viscoelastic behavior was related both to the water‐sorption processes and to the microstructure of the system. An important impact of water uptake on the tensile properties at break was also appreciated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 71–80, 2001     

Dielectric properties of an epoxy resin and its composite I. Moisture effects on dipole relaxation

Dipole relaxation dielectric loss behavior of a fiberglass–epoxy composite has been studied as a function of moisture uptake. A single widely distributed loss peak, centered at ?16°C for 10 kHz measurement, is observed in the dry composite. Very low moisture concentrations (<0.1%) interact with the composite, through either dipole pairing or by inducing chemical changes, to decrease loss intensity. At moisture concentrations from 0.1 to 1.4%, loss peak intensity generally increases with moisture uptake. Over this moisture concentration range water dipoles presumably relax in phase with the epoxy segments or side groups upon which they adsorb. Arrhenius relaxation activation energy decreases, and improved loss peak definition at increasing moisture concentrations is interpreted as indicating resin plasticization by adsorbed moisture. At moisture concentrations above 1.4%, the appearance of a second loss peak suggests formation of a new colloidal or weakly adsorbed moisture phase, as well as the saturation of primary adsorption sites.     

微晶纤维素含量对PE-HD复合材料性能的影响

采用熔融共混法制备了微晶纤维素（MCC）含量分别为50 ％、60 ％和70 ％的高密度聚乙烯（PE-HD）/MCC复合材料,研究了MCC含量对其力学性能、流变行为、热变形温度和断口形貌的影响。结果表明,加入MCC能有效提高PE-HD的弯曲强度、弯曲模量和拉伸强度,其中MCC含量为60 ％时材料力学性能最好;MCC的加入显著提高了PE-HD的热变形温度,且MCC含量为60 ％时复合材料热变形温度最高;PE-HD/MCC复合材料断口形貌分析表明MCC在基体中分布较均匀,MCC含量为60 ％时与PE-HD基体的相容性最好。     

Mechanical properties of biodegradable composites from poly lactic acid (PLA) and microcrystalline cellulose (MCC)

Biodegradable composites were prepared using microcrystalline cellulose (MCC) as the reinforcement and polylactic acid (PLA) as a matrix. PLA is polyester of lactic acid and MCC is cellulose derived from high quality wood pulp by acid hydrolysis to remove the amorphous regions. The composites were prepared with different MCC contents, up to 25 wt %, and wood flour (WF) and wood pulp (WP) were used as reference materials. Generally, the MCC/PLA composites showed lower mechanical properties compared to the reference materials. The dynamic mechanical thermal analysis (DMTA) showed that the storage modulus was increased with the addition of MCC. The X‐ray diffraction (XRD) studies on the materials showed that the composites were less crystalline than the pure components. However, the scanning electron microscopy (SEM) study of materials showed that the MCC was remaining as aggregates of crystalline cellulose fibrils, which explains the poor mechanical properties. Furthermore, the fracture surfaces of MCC composites were indicative of poor adhesion between MCC and the PLA matrix. Biodegradation studies in compost soil at 58°C showed that WF composites have better biodegradability compared to WP and MCC composites. The composite performances are expected to improve by separation of the cellulose aggregates to microfibrils and with improved adhesion. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2014–2025, 2005