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The non-isothermal DSC method was used to deduce the curing process parameters of self-made low-viscosity phenolic modified amine curing agent and epoxy resin, and verified by the curing degree of the test system. The cured product was characterized by infrared spectroscopy. The mechanical properties and thermal properties (TG) of the castable were measured at the same time. The surface morphology of the tensile fracture surface was observed by scanning electron microscope (SEM). The results show that the mass ratio of epoxy resin E-51 and self-made curing agent is 100:35, the curing process conditions are normal temperature/24h+80°C/2h, the mechanical properties of the system are the best, the tensile strength is 55.2MPa, the bending strength is 92.8 MPa, compressive strength 83.0 MPa, elongation at break 2.2%, Tg reached 280.3°C. The curing agent has low viscosity, good heat resistance and good flexibility and can be used for building structural adhesives.
Phenalkamine is a product of Mann-phase reaction of an amine with a phenol and an aldehyde. Since the molecular structure of the reaction product contains a phenolic hydroxyl group, an amino group (-NH2), and a secondary amino group (-NH-), curing agents of this type are cured. Fast, cures at low temperatures, humidity, or underwater. According to different types of amines, phenols, and aldehydes, different reactant ratios, different process routes, different reaction conditions, and different control endpoints, a series of different modified amine curing agents can be produced to make them cured with epoxy resin. Different performance characteristics [1, 2]. At present, in the market of epoxy resin building structural adhesives, commercially available T-31 curing agents are generally obtained by simple one-step reaction of phenol, formaldehyde, low molecular amine ethylenediamine, due to high activity and relatively low price. It is used extensively. However, with the issuance of the “Code for Acceptance of Construction Quality of Reinforced Building Structures†(GB50550-2010), the curing products of such curing agents and epoxy resins are high in brittleness and poor in toughness, and their comprehensive performance is lacking, and it is difficult to meet new requirements. To this end, we used cresols, acetaldehyde, and diethylenetriamines to synthesize a low molecular weight phenolic modified amine epoxy curing agent using a Mannich reaction. The curing agent has a low viscosity, a moderate curing speed, and a cured product. Good thermal and mechanical properties, high cost-effective curing agent and other advantages. Because the self-made epoxy curing agent introduces some inactive functional groups to make the curing system show good toughness, it can be used as a building structural adhesive.
The epoxy resin and curing agent are mixed at a certain ratio, and then cured at room temperature for 24 hours, then placed in an incubator and cured according to the set temperature and time. The smashed samples are weighed and packaged separately in a slow ration filter paper. , and then placed in the Soxhlet extractor, extracted with acetone reflux 2h, dry to a constant weight and weighed, according to the following formula to calculate the degree of cure:
Degree of cure=(m3-m1)/(m2-m1)×100%
Where: mass of m1-filter paper, g; total mass of filter paper and sample before m2-propanone extraction, g; total mass of filter paper and sample after m3-acetone extraction, g.
Determination of mechanical properties
Tensile strength is measured according to GB/T6329-1996; flexural strength, compressive strength according to GB/T2567-2008 resin casting body performance test method.
Infrared Spectroscopy (FT-IR) Analysis
When the epoxy resin and the curing agent are initially mixed, a liquid film method is used; after the curing, the KBr tableting method is used.
Thermal analysis
DSC analysis: After mixing uniformly with m (epoxy resin E-51):m (self-made curing agent)=100:35, sample immediately for DSC analysis, N2 atmosphere, heating rate 5°C/min, 10°C/min, respectively , 20°C/min, temperature 25 to 300°C. Thermal gravimetric analysis (TG): Take 6-8 mg of solidified sample in aluminum crucible and compare it with empty aluminum crucible. N2 flow rate is 20 mL/min, heating rate is 10°C/min, and temperature rise range is 40-800°C.
Scanning electron microscope analysis
The tensile fracture surface of the cured product was taken, and the surface morphology of the tensile fracture surface was analyzed after removing the surface impurities by deionized water for 20 min under ultrasonic waves.
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