Kraft lignin and polyethylene terephthalate blends: effect on thermal and mechanical properties

Lazzari, Lívia; Domingos, Eloilson; Silva, Letícia; Kuznetsov, Alexei; Romão, Wanderson; Araujo, Joyce

doi:10.1590/0104-1428.06618

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ORIGINAL ARTICLE • Polímeros 29 (4) • 2019 • https://doi.org/10.1590/0104-1428.06618 copy

Kraft lignin and polyethylene terephthalate blends: effect on thermal and mechanical properties

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

In this work, bottle-grade poly(ethylene terephthalate) (PET_R), kraft lignin (KL), and chemically modified lignin (ML) were used to form blends to improve the mechanical and thermal properties of pure PET. The PET/KL and PET_R/ML blends were produced with 0.5, 1, 3, and 5 wt.% of lignin via melt extrusion and injection molding. The produced blends and PET_R were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TGA), differential scanning calorimetry (DSC) and mechanical properties testing. The FTIR measurements confirmed the chemical modifications of the ML samples, while the TGA results showed KL to be thermally more stable than ML. The glass transition temperature of PET_R changed as a function of the amount of lignin, as revealed by the DSC measurements. The PET/KL blends demonstrated their potential for use as an engineering material due to their improved thermal and mechanical properties compared to those of PET_R.

Keywords:
blends; kraft lignin; mechanical properties; poly(ethylene terephthalate)

Sample	PET_R (wt.%)	KL (wt.%)	ML (wt.%)	Formulation^* * PETR: bottle-grade poly(ethylene terephthalate), KL: kraft lignin, and ML: chemically modified lignin.
1	100	0	0	PET_R
2	99.5	0.5	0	PET/KF 0.5 wt.%
3	99	1.0	0	PET/KF 1.0 wt.%
4	97	3.0	0	PET/KF 3.0 wt.%
5	95	5.0	0	PET/KF 5.0 wt.%
6	99.5	0	0.5	PET/ML 0.5 wt.%
7	99	0	1.0	PET/ML 1.0 wt.%
8	97	0	3.0	PET/ML 3.0 wt.%
9	95	0	5.0	PET/ML 5.0 wt.%

Wavenumber (cm^-1)	Assignment
3413	OH group (hydroxyl)
2934	aliphatic C-H asymmetric stretching
1710	C=O stretch of carboxylic acids, ketones, and aldehydes
1603	C=C aromatic stretching
1505	C=C aromatic stretching
1454	CH₂CH₃ bending
1211	C-O phenolic stretching
1110	C-O stretching of the aliphatic secondary alcohol chain
1019	C-O stretching of the primary alcohol aliphatic chain

Wavenumber (cm^-1)	Assignment
3254	OH group (hydroxyl)
2938	aliphatic C-H asymmetric stretching
1598	asymmetric carboxylate stretching
1416	symmetrical carboxylate stretch
1507	C=C aromatic stretches
1453	CH₂CH₃ bending
1249	C-O phenolic stretching
1123	C-O stretching of the aliphatic secondary alcohol chain
1031	C-O stretching of the primary alcohol aliphatic chain

Sample	T_g (°C)*	T_c (°C) ^* * Tg, Tc, Tm, ΔHm and Xc correspond to glass transition temperature, crystallization temperature, melting temperature, melting enthalpy, and degree of crystallinity, respectively.	T_m (°C)*	ΔH_m (J/g)*	X_c (%)*
PET_R	63.30	119.50	253.79	-4.45	3.18%
PET/KF 0.5wt.%	70.29	117.37	257.18	-4.90	3.52%
PET/KF 1.0wt.%	69.70	116.42	256.59	-5.49	3.96%
PET/KF 3.0wt.%	68.34	116.89	256.49	-5.89	4.34%
PET/KF 5.0wt.%	68.80	117.99	253.09	-5.94	4.46%
PET/ML 0.5wt.%	74.96	113.61	255.02	-5.71	4.10%
PET/ML 1.0wt.%	74.76	113.05	258.26	-5.26	3.80%
PET/ML 3.0wt.%	74.77	110.46	258.15	-5.66	4.17%
PET/ML 5.0wt.%	74.98	109.45	256.34	-5.70	4.29%

Sample	E (GPa)**	ΔE (GPa) ^ E: modulus of elasticity; ΔE: standard deviation of modulus of elasticity; σ: maximum tensile strength; Δσ: standard deviation of maximum tensile strength; ε𝑟𝑢𝑝: strain at break; Δε𝑟𝑢𝑝: standard deviation of strain at break.	σ (Mpa)**	Δσ (Mpa)**	ε_rup %**	Δε_rup %**
PET_R	1.33	±0.04	57.31	±0.60	NB*	NB^* * did not break;
PET/KF 0.5 wt.%	1.47	±0.06	60.20	±0.85	NB*	NB*
PET/KF 1.0 wt.%	1.55	±0.05	61.62	±0.67	NB*	NB*
PET/KF 3.0 wt.%	1.71	±0.05	39.56	±1.28	2.0	±0.54
PET/KF 5.0 wt.%	1.76	±0.12	37.77	±2.80	2.1	±0.29
PET/ML 0.5 wt.%	1.66	±0.29	20.59	±3.60	0.9	±0.16
PET/ML 1.0 wt.%	1.43	±0.22	20.41	±1.78	1.1	±0.40

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[1] * jraraujo@inmetro.gov.br