Question
Asked 17th May, 2016

Curing of Epoxy resin and its strength?

i have done experiment on curing of epoxy L12 Hardener k6..Made a Neat composite..Ratio taken 10:1...But while checking tensile strength of neat composite i obtained very less values (23-30) as compared with company standard values of 60-70..What will be problem during the curing process..Any suggestions

Most recent answer

3rd Mar, 2020
Ashish Thakur
Mekelle University
Dear Kashahun,
The main difference between (Epoxy and Epoxy resin) both adhesive types is the drying time. Both epoxy and resin adhesives require mixing before use, but epoxy hardens much faster than resin glue. Resin glues take longer to cure, about 8-10 hours, while epoxy adhesive only takes about 6-30 minute.
Curing of epoxy resins is an exothermic reaction and in some cases produces sufficient heat to cause thermal degradation if not controlled. Curing may be achieved by reacting an epoxy with itself (homopolymerisation) or by forming a copolymer with polyfunctional curatives or hardeners. Epoxy cuts easiest after 24 hours of cure, but before 48 hours or more: it has cured enough to be cut, but has not reached full mechanical properties. Epoxy's hardness dulls sandpaper fast. In addition, cured epoxy can quickly fill sandpaper, rendering it ineffective after several swipes.
Epoxies will harden in minutes or hours, but complete cure (hardening) will generally take several days. Most epoxies will be suitably hard within a day or so, but may require more time to harden before the coating can be sanded.
A useful way to look at a cured epoxy is to carry out differential scanning calorimetry (DSC). DSC measures the energy input or output of the solid resin as it is scanned from low to high temperatures. High Strength Epoxy Utilizes Renewable Biomaterial: EP70CN. “The tensile strength is 11,000 to 12,000 psi and the tensile modulus, 300,000 to 350,000 psi. It features a glass transition temperature of 130 to 135°C”. Epoxy-based materials are different from standard concrete in a few ways. One of the primary things is the strength. When the epoxy is cured and hardened, it cures around 10,000 psi. Depending on the temperature, epoxy generally cures between 24 to 72 hours. Epoxy sealers form a high-build protective film on the concrete surface, producing a hard, long-wearing, abrasion-resistant finish. Water-based epoxies bond well to concrete and provide a clear finish, but they are nonporous and do not allow trapped moisture to escape.
Hope it is helpful to you.
Ashish
i
1 Recommendation

Popular Answers (1)

20th May, 2016
Alexandra Wätzig
Tadano Faun
Dear Linto,
I´ve seen, you already got several notes. In general it is absolutely necessary to very strictly adhere to the stoichiometric ratio given by the manufacturer. Any remaining uncrosslinked contents of resin or hardener can act as softener in the cured epoxy and strongly decrease the mechanical properties. Are there further any details mentioned by the manufacturer regarding the cure cycle? Often an additional short-term post-curing at elevated temperatures is recommended for a full hardening and therefore significantly enhances the properties. Moreover, porosities due to e.g. incorporated air in the blending process of the components can lead cracks and thus to an ealy failure. 
Best regards
Alexandra
3 Recommendations

All Answers (12)

18th May, 2016
Edwin A. Murillo
Universidad Francisco de Paula Santander
You can increase the catalyzer amount, futhermore is very important that you make cured kinetic by DSC or TGA. 
18th May, 2016
Pramod Vadavkar
Savitribai Phule Pune University
Dear Linto,
Refer to the data sheet for the ratio, curing details, post curing instructions etc.
was the tensile test sample cut properly, were the resin and hardener mixed properly, So much deterioration is not possible
You have not mentioned the manufacturer of the resin system.
18th May, 2016
Matthias Jaunich
Bundesanstalt für Materialforschung und -prüfung
Some discussion concerning the benefits of a detailed kinetic analysis can be found here:
Additionally you can check for homogenous mixing.
best regards
Matthias
1 Recommendation
20th May, 2016
Padmanabhan Krishnan
VIT University
Added to the above answers, please monitor shelf life and pot life. Are the resin  and the hardener free from moisture ?
20th May, 2016
Alexandra Wätzig
Tadano Faun
Dear Linto,
I´ve seen, you already got several notes. In general it is absolutely necessary to very strictly adhere to the stoichiometric ratio given by the manufacturer. Any remaining uncrosslinked contents of resin or hardener can act as softener in the cured epoxy and strongly decrease the mechanical properties. Are there further any details mentioned by the manufacturer regarding the cure cycle? Often an additional short-term post-curing at elevated temperatures is recommended for a full hardening and therefore significantly enhances the properties. Moreover, porosities due to e.g. incorporated air in the blending process of the components can lead cracks and thus to an ealy failure. 
Best regards
Alexandra
3 Recommendations
21st May, 2016
Hareesh Ananthakeshavachar
K.S. School of Engineering and Management
please check the ambient temperature,humidity.
24th May, 2016
M. Ali Aravand
KU Leuven
 In addition to the above notes, it is always recommended to perform some characterisations with new resin/hardener systems. For instance, a DSC measurement can reveal any traces of uncured resin (look for typical resin exho and thermo peaks) or incomplete reaction. Basically no exothermic reaction within the curing temperature range of a supposedly cured sample should be identified. To define your curing profile, you can either rely on the data sheet, or do your own measurements through rheometry (temp. ramp to find the curing point, and isothermal measurements of the storage and damping moduli for curing time). 
3rd Feb, 2020
Kassahun Gashu Melese
Hawassa University Institute of Technology
I have to face this problem in my work epoxy LY 556 and XIN 100 with their hardeners but I keep the room temperature and proper mixing with hardener. The slower curing epoxy forms longer molecular chains as it cures which results in more strength. As to waterproofing, cure speed has little or no effect, all are relatively waterproof. note that all epoxies, even the 5-minute cure type, do not gain full strength for about 12 to 24 hours depending on temperature.
3rd Mar, 2020
Kassahun Gashu Melese
Hawassa University Institute of Technology
In the curing process, thermosetting resin systems shrink owing to cross-linking and temperature change so that their density increases. Taking the epoxy resin system as an example, its volume change is shown in the specific volume-T curve. A fabrication process of Epoxy/composites at room temperature is less than the Tg (glass transmission) and Curing time range .

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