Toughening of epoxy resin using hydroxyl-terminated polyesters

Abstract

Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by relatively low toughness. Several approaches to improve epoxy resin toughness include the addition of fillers, rubber particles, thermoplastics, or their hybrids, as well as interpenetrating networks and flexibilizers, such as polyols. It seems that this last approach did not receive much attention. So in an attempt to fill this gap, the present work deals with the use of hydroxyl-terminated polyester resins as toughening agents for epoxy resin. For this purpose, the modifier, that is, a hydroxylterminated polyester resin (commercially referred to as Desmophen), which is a polyol, has been used at different concentrations. The prepared modified structure has been characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. Two types of Desmophen (800 and 1200) have been used as modifiers. The obtained results showed that hydroxyl-terminated polyester improves the epoxy toughness. In fact, the impact strength increases with Desmophen content and reaches a maximum value of 7.65 J/m at 10 phr for Desmophen 800 and 9.36 J/m at 7.5 phr for Desmophen 1200, respectively. At a critical concentration (7.5 phr), Desmophen 1200 (with higher molecular weight, longer chains, and lower branching) leads to better results. Concerning K c , the effect of Desmophen 800 is almost negligible; whereas a drastic effect is observed with Desmophen 1200 as K c reaches a maximum of 2.41 MPa m 1/2 , compared to 0.9 MPa m 1/2 of the unmodified epoxy prior to decreasing. This is attributed to the intensive hydrogen bonding between epoxy and Desmophen 1200, as revealed by FTIR spectroscopy. Finally, the SEM analysis results suggested that the possible toughening mechanism for the epoxy resin being considered, which might prevail, is through localized plastic shear yielding induced by the presence of the Desmophen particles.

Miscibility, morphology, thermal, and mechanical properties of a DGEBA based epoxy resin toughened with a liquid rubber

“…This may lead to an increase in toughness of the epoxy network. The toughness enhancement is also due to the increase in degree of entanglement between the resin and the rubber [34]. Increase in main chain mobility also favors the property improvement [35].…”

“…The rubber that is incorporated into the resin matrix is responsible for the reduction in flexural strength of the modified samples. Previous works on rubber-modified epoxies support this observation [8,9,34,47,48].…”

Mesostructured silica for the reinforcement and toughening of rubbery and glassy epoxy polymers

“…Due to their amorphous structure, these thermoset polymers generally exhibit relatively poor toughness in comparison to semi-crystalline thermoplastics. The incorporation of thermoplastics [1] or elastomers [2][3][4] into an epoxy matrix can be an effective way to improve toughness, but it can compromise strength or modulus. Functional fillers, such as organoclays [5,6] and related organosilica particles [7], also can improve the toughness of an epoxy resin, but the need for an organic surface modifier to achieve particle dispersion adds to the cost of such fillers.…”

The influence of epoxy resin on the morphological and rheological properties of PET/PA66 blend

“…The FTIR spectra of original form of epoxy resin and PET are presented in Fig. 7a and b. the peaks of C=O at 1740, OH at 3,520 and COOH at 3,290 are the characteristic peaks of PET (Al-AbdulRazzak et al 2002); similarly, the peaks of CH3 bending at 1360, OH at 3,510 and the peaks at 880 and 915, which represent epoxy ring, are the characteristic peak of epoxy resin (Harani et al 1999;Tripathi and Srivasta 2007). Figure 7c shows the FTIR spectra of PET/EP1% after 1 min mixing in mixer and rinsing to remove unreacted epoxy.…”

“…The peak at 3,389 is due to the N-H vibration, overlapped with the OH band of epoxy. The shifts of N-H and OH band could stem from the H-bonding between N-H and OH (Harani et al 1999). The appearance of these characteristic peaks assigned to PA66 chains after etching of dispersed phase could reveal the reaction between PET/EP and PA66 and producing PET/PA66 copolymer at the interface of the blend.…”