Issue 55

P. Santos et alii, Frattura ed Integrità Strutturale, 55 (2021) 198-212; DOI: 10.3221/IGF-ESIS.55.15

the hardener chemical components were not indicated for the latter one. In this sense, Tab. 2 summarizes all the known relevant information about the chemical compositions of the two resin formulas obtained from the datasheet, and Fig. 1 shows their chemical structures.

Property

Sicomin SR 8100/SD 8824 Ebalta AH 150/IP430

Colour

Light yellow liquid

Opaque 250 ± 50

Viscosity (@ 25 ºC)

[mPa×s] [g/cm 3 ] [N/mm 2 ] [N/mm 2 ]

285 ± 60

Density at 20 ºC

-

1.13  ± 0.02 3400 ± 300

2970

Modulus of elasticity Maximum resistance Elongation at max. load Elongation at break Charpy impact strength Glass transition / DCC

108

125 ± 1.2

[%] [%]

4.9

-

11.8

5.9 ± 0.1

[kJ/m 2 ]

52 63

60 ± 6

[ºC] [%]

-

Water absorption 48 h/70 °C

1.2 - Table 1: Main mechanical and physical properties of the epoxy resins.

Type of component

Identification number CAS: 1675-54-3 EC: 216-823-5

Sicomin SR 8100/SD 8824

Ebalta AH 150/IP430

bisphenol A epoxy resin (DGEBA)

Composition: % not specified MW ≤ 700

Composition: 10 <= x % < 25

Resin

bisphenol F epoxy resin (DGEBF)

CAS.: 9003-36-5 EC: 500-006-8

Composition: % not specified MW ≤ 700

Composition: 50 <= x % < 100

1,6-bis(2,3-epoxypropoxy)hexane

CAS: 16096-31-4 EC: 240-260-4 CAS: 15520-10-2 EC: 239-556-6 CAS: 1477-55-0 EC: 216-032-5 CAS: 39423-51-3 EC: 500-105-6

Diluent

Composition: 10 <= x % < 25 2-methylpentane-1,5-diamine Composition: 25 <= x % < 50 m-phenylenebis(methylamine) Composition: 25 <= x % < 50

Composition: % not specified

Hardener: amines

Composition: Molecules and % not specified

trimethylolpropane tris[poly(propylene glycol), amine terminated] ether Composition: 2.5 <= x % < 10 Table 2: Chemical composition of the epoxy resins, diluent and hardeners used in this study based on the data known from their technical datasheets. Regarding the carbon nanofibers (CNFs), their technical specifications are summarized in Tab. 3 and Fig. 2 shows the SEM images of the CNFs used in this study. In terms of dimensions, as shown, the average diameter is about 130 nm, the length ranges from 20 to 200 µm and the average specific surface area around 54 m 2 /g. In terms of manufacture process, and after weighing, CNFs were added to the epoxy resin and several contents by weight were studied: 0.25, 0.5, 0.75 and 1 %. The dispersion into the resin was conducted using, simultaneously, a high-speed shear mixer at a shear rate of 1000 rpm and sonication (using an ultrasonic bath with a frequency of 40 kHz) for 3 hours at room temperature. This procedure took another 10 minutes, with a rotation speed of just 150 rpm, to mix the hardener into the system. The low rotation speed aimed to minimize the formation of air bubbles and to promote only a homogeneous mixture of the hardener into the system. The rotation speed and time of mixture were optimized in previous studies. The

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