Green Polyethylene in Harsh Environments: Gamma-irradiation Effects

Medeiros, Pablo R. de; Araujo, Patricia L. B.; Aquino, Katia A. S.; Araujo, Elmo S.

doi:10.1590/1980-5373-MR-2022-0186

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Article • Mat. Res. 25 • 2022 • https://doi.org/10.1590/1980-5373-MR-2022-0186 copy

Green Polyethylene in Harsh Environments: Gamma-irradiation Effects

Authorship SCIMAGO INSTITUTIONS RANKINGS

Bio-based linear low-density polyethylene (green LLDPE) composites are used as electrical jackets/insulator for cables. Assessments of gamma-irradiation (Co-60) effects on these materials are of interest as they might be used in nuclear power plants (NPPs). Brazilian sugarcane juice-based green LLDPE composite electrical jackets were irradiated until 1000 kGy and analyzed for thermal stability and mechanical characteristics. Thermogravimetry analysis (TGA) showed increasing of pyrolysis activation energy (E_a) (under N₂) from 42.7 ± 4.2 kJ/mol in unirradiated samples to 72.8 ± 4.6 kJ/mol after 60 kGy dose, as resulted of radiation-induced effects. FTIR spectra evidenced radiation-induced formation of conjugated C=C bonds after 250 kGy dose. Tensile stress and Young modulus did not change significantly until 150 kGy dose, whereas elongation at break decreased and reached 50% at 91 kGy dose. These results suggest that green LLDPE might withstand radiation damage through a NPP operating life (~ 40 years).

Keywords:
bio-based plastics; gamma radiation; LLDPE thermal properties; LLDPE mechanical properties; nuclear power plants

Method	p(y)-approximation	A	k	Reference
Starink	Starink	1.008	1.92	27
Starink	$p (y) ≅ \frac{\exp (- 1.008 y - 0.312)}{y^{1.92}}$	1.008	1.92	27
Kissinger-Akahira-Sunose (KAS)	Murray and White	1	2	28-30
Kissinger-Akahira-Sunose (KAS)	$p (y) ≅ \frac{\exp (- y)}{y^{2}}$	1	2	28-30
Flynn-Wall-Ozawa (FWO)	Doyle	1.0518	0	31-35
Flynn-Wall-Ozawa (FWO)	$p (y) ≅ \exp (- 1.0518 y - 5.330)$	1.0518	0	31-35

Atmosphere	Dose (kGy)	T_onset (°C)	T_max (°C)	R_max (% mass- loss.min^-1)	Entry
Nitrogen	unirradiated	384	457	10	1
	60	390	462	12	2
	250	391	461	12	3
Oxygen	unirradiated	368	371	58	4
	60	374	376	113	5
	250	384	398	60	6

Conversion x	E_a (kJ/mol) N₂	E_a (kJ/mol) O₂
0.2	39.5	43.1
0.3	38.2	41.5
0.4	38.7	41.0
0.5	41.8	40.4
0.6	44.7	39.1
0.7	47.1	38.2
0.8	48.8	37.4
	42.7 ± 4.2	40.1 ± 2.0

Atmosphere	Dose (kGy)	Activation energy (kJ.mol^-1)	Entry
Nitrogen	0	42.7 ± 4.2	1
	60	72.8 ± 4.6	2
	250	67.0 ± 1.7	3
Oxygen	0	40.1 ± 2.0	4
	60	51.4 ± 3.4	5
	250	112.5 ± 11.6	6

Mathematical function	y₀	a	b	r²
$y = y_{0} + a . e^{(- b x)}$	14.821±8.387	107.037±11.079	0.009±0.003	0.949
Statistical tests
Normality test (Shapiro-Wilk)		Passed (P = 0.2564)
W Statistic = 0.8943 Significance level (<0.0001)
Constant variance test		Passed (P = 0.0096)

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[1] *e-mail: elmo.araujo@ufpe.br