A novel hybrid linear-hyperbranched poly(butylene adipate) copolymer as an epoxy resin modifier with toughening effect

Novel Reactive Polyhedral Oligomeric Silsesquioxane-Reinforced and Toughened Epoxy Resins for Advanced Composites

Most toughening methods for epoxy resins are usually used at the expense of other properties. Some polyhedral oligomeric silsesquioxanes (POSSs) with both a rigid Si-O-Si structure and flexible organic chain segments could be expected to be effective toughening agents. In this study, three reactive polyhedral oligomeric silsesquioxanes with a thiol group (OMPPS), a carboxyl group (OCOPS), and an epoxy group (OGCPS) were synthesized and characterized. They were utilized as modifiers to toughen 3-(oxiran-2-ylmethoxy)-N,N-bis(oxiran-2-ylmethyl)aniline (AFG-90MH)/4,4'-methylenebis(2-ethylaniline) (MOEA) (epoxy resin) with different molar ratios to obtain hybrid resins named OMPPS-EP-i, OCOPS-EP-j, and OGCPS-EP-k. The effects of the amount of modifier added and the length of the organic chain on the cage structure on various properties of the hybrid resins were investigated. The results show that all three modifiers show good compatibility with the epoxy resin. The hybrid resins have a low viscosity at 45~85 °C and can be cured at a low temperature (110 °C). The cured hybrid resins display improved toughness. Typically, the critical stress intensity factor (KIC) and impact strength of OGCPS-EP-0.6-C are 2.54 MPa∙m-1/2 and 19.33 kJ∙m-2, respectively, which increased by 58.75% and 22.48% compared with the pristine epoxy resin, respectively. In addition, the glass transition temperature and flexural strength of the hybrid resins are basically unchanged.

Investigations into the characterization, degradation, and applications of biodegradable polymers by mass spectrometry

Biodegradable polymers have been getting more and more attention because of their contribution to the plastic pollution environmental issues and to move towards a circular economy. Nevertheless, biodegradable materials still exhibit various disadvantages restraining a widespread use in the market. Therefore, additional research efforts are required to improve their performance. Mass spectrometry (MS) affords a relevant contribution to optimize biodegradable polymer synthesis, to confirm macromolecular structures, to examine along the time the progress of degradation processes and highlight advantages and drawbacks in the extensive applications. This review aims to provide an overview of the MS investigations carried out to support the synthesis of biodegradable polymers, with helpful information on undesirable products or polymerization mechanism, to understand deterioration pathways by the structure of degradation products and to follow drug release and pharmacokinetic. Additionally, it summarizes MS studies addressed on environmental and health issues related to the extensive use of plastic materials, that is, potential migration of additives or microplastics identification and quantification. The paper is focused on the most significant studies relating to synthetic and microbial biodegradable polymers published in the last 15 years, not including agro-polymers such as proteins and polysaccharides.

Toughening of Epoxy Systems with Interpenetrating Polymer Network (IPN): A Review

Epoxy resins are widely used for different commercial applications, particularly in the aerospace industry as matrix carbon fibre reinforced polymers composite. This is due to their excellent properties, i.e., ease of processing, low cost, superior mechanical, thermal and electrical properties. However, a pure epoxy system possesses some inherent shortcomings, such as brittleness and low elongation after cure, limiting performance of the composite. Several approaches to toughen epoxy systems have been explored, of which formation of the interpenetrating polymer network (IPN) has gained increasing attention. This methodology usually results in better mechanical properties (e.g., fracture toughness) of the modified epoxy system. Ideally, IPNs result in a synergistic combination of desirable properties of two different polymers, i.e., improved toughness comes from the toughener while thermosets are responsible for high service temperature. Three main parameters influence the mechanical response of IPN toughened systems: (i) the chemical structure of the constituents, (ii) the toughener content and finally and (iii) the type and scale of the resulting morphology. Various synthesis routes exist for the creation of IPN giving different means of control of the IPN structure and also offering different processing routes for making composites. The aim of this review is to provide an overview of the current state-of-the-art on toughening of epoxy matrix system through formation of IPN structure, either by using thermoplastics or thermosets. Moreover, the potential of IPN based epoxy systems is explored for the formation of composites particularly for aerospace applications.

Effect of structure regulation of hyper-branched polyester modified carbon nanotubes on toughening performance of epoxy/carbon nanotube nanocomposites

In this paper, carboxylic multi-walled carbon nanotubes (MWCNTs-COOH) were modified by a series of hyperbranched polyesters (HBP) with different molecular structures (different branching degree) through surface grafting, and then the epoxy resin (EP)/carbon nanotube composites were prepared to explore the influences of structure regulation of HBP modified carbon nanotubes on the toughening performance of the composites. The results of Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) of various HBP grafted carbon nanotubes confirmed that the HBP were successfully grafted onto MWCNTs-COOH via an esterification reaction between the carboxyl groups of MWCNTs-COOH and the hydroxyl groups of HBP, meanwhile, the higher the branching degree of the HBP, the higher its grafting ratio onto carbon nanotubes. Furthermore, the outcome of dynamic thermal mechanical analysis (DMA) indicated that the addition of MWCNTs-COOH increased the storage modulus and glass transition temperature (T_g) of the pure EP, and surface grafting of various HBP onto MWCNTs-COOH decreased the T_g and peak height of mechanical loss of composites. And as the branching degree of HBP increased, the interfacial bonding between MWCNTs and the EP matrix became stronger. The results of mechanical performance and morphology analysis also revealed that the addition of HBP grafted MWCNTs-COOH significantly improved its dispersion and interfacial bonding in the EP matrix, resulting in better performance in the enhancement of toughness of the composites. In addition, it was found that the higher the branching degree of HBP, the better the toughening performance of the composites.

Carboxylic carbon nanotubes were modified by a series of hyperbranched polyesters (HBP), and epoxy resin/carbon nanotubes composites were prepared. The effect of structure regulation of HBP on toughening properties of composites was discussed.

Investigation on cure kinetics of epoxy resin containing carbon nanotubes modified with hyper-branched polyester

The cure kinetics of epoxy resin cured by diethyltoluene diamine (D-EP), D-EP/multi-walled carbon nanotube (D-EP/CNT) composites and D-EP/hyper branched polyester functionalized CNTs (D-EP/CNTs-H20) were investigated by non-isothermal differential scanning calorimetry (DSC). Results revealed that the presence of CNTs shifted the cure temperature to a lower temperature and accelerated the curing of D-EP, and the addition of CNTs-H20 exhibited a stronger effect in accelerating the cure of D-EP. Activation energies were calculated based on the Kissinger approach and Ozawa approach respectively. Lowered activation energy was observed after the addition of CNTs or CNTs-H20 at low degrees of cure, indicating that the CNTs had a large effect on the curing reaction. The presence of CNTs facilitated the curing reaction, especially the initial epoxyamine reaction. Moreover, CNTs-H20 exhibited better performance. The autocatalytic model was used to describe the cure kinetics phenomena of the studied systems. When CNTs or CNTs-H20 were added, the Sesták–Berggren model still can describe the cure kinetics of the D-EP composites because the results, calculated by the model, agreed with the experimental data well. Moreover, the kinetics parameters as well as the equation describing the cure process were proposed.

The cure kinetics of epoxy resin cured by D-EP, D-EP/CNT composites and D-EP/CNTs-H20 were investigated by non-isothermal differential scanning calorimetry (DSC).