Abstract:Poly(vinilidene fluoride) was characterized before and after stress relaxation by tensile tests and time-domain nuclear magnetic resonance (TD-NMR). Tensile tests were performed to provide mechanical properties, focused on the data of elastic modulus for this matter. The TD-NMR technique was used to calculate the fraction of crystalline, constrained amorphous and free amorphous phase, and the transversal relaxation time of each of these phases.
“…The evidence of compounds containing aromatic structures was confirmed by analyses conducted by Montaudo et al [31] and O 0 shea et al [32]. Besides, if PVDF is synthesized from the persulfate initiator (emulsion process) [19,20], sulfate end-groups are present and should undergo thermal depolymerization by unzipping from these poorly thermostable end-groups.…”
Section: Thermal Degradation Kineticsmentioning
confidence: 81%
“…[ 32 ]. Besides, if PVDF is synthesized from the persulfate initiator (emulsion process) [ 19 , 20 ], sulfate end-groups are present and should undergo thermal depolymerization by unzipping from these poorly thermostable end-groups. Figure 5 Reconstruction of the mechanism of H–F elimination followed by polyaromatization of PVDF during its thermal degradation.…”
Section: Resultsmentioning
confidence: 99%
“…The nonpolar α -form PVDF has its use well consolidated in structural applications such as flexible pipes for oil and gas exploration [ 11 , 12 , 13 , 14 ]. PVDF can also be employed as a liner (coating) or inner layer in multilayers thermoplastic pipes or storage tanks dedicated to storage and/or transportation of biofuels, mixtures of biofuels-gasoline and sodium hydroxide solutions (except in critical conditions, i.e., temperature range from 50 to 90 °C and pH of 13.5–14), among others [ 5 , 7 , 13 , 15 , 16 , 17 , 18 , 19 , 20 ]. Additionally, PVDF has several other industrial uses, including valves, membrane filters, pumps and bearings, chemicals and pharmaceuticals packaging, and barrier for gaseous substances [ 7 , 8 , 19 , 21 ].…”
PVDF was prepared by compression molding, and its phase content/structure was assessed by WAXD, DSC, and FTIR-ATR spectroscopy. Next, PVDF samples were aged in bioethanol fuel at 60 °C or annealed in the same temperature by 30 ─ 180 days. Then, the influence of aging/annealing on thermal stability, thermal degradation kinetics, and lifetime of the PVDF was investigated by thermogravimetric analysis (TGA/DTG), as well as the structure was again examined. The crystallinity of ~41% (from WAXD) or ~49% (from DSC) were identified for unaged PVDF, without significant changes after aging or annealing. This PVDF presented not only one phase, but a mixture of
α
-,
β
- and
γ
-phases,
α
- and
β
-phases with more highlighted vibrational bands. Thermal degradation kinetics was evaluated using the non-isothermal Ozawa–Flynn–Wall method. The activation energy (
E
a
) of thermal degradation was calculated for conversion levels of
α
= 5 ─ 50% at constant heating rates (5, 10, 20, and 40 °C min
─1
),
α
= 10% was fixed for lifetime estimation. The results indicated that temperature alone does not affect the material, but its combination with bioethanol reduced the onset temperature and
E
a
of primary thermal degradation. Additionally, the material lifetime decreased until about five decades (
T
f
= 25 °C and 90 days of exposition) due to the fluid effect after aging.
“…The evidence of compounds containing aromatic structures was confirmed by analyses conducted by Montaudo et al [31] and O 0 shea et al [32]. Besides, if PVDF is synthesized from the persulfate initiator (emulsion process) [19,20], sulfate end-groups are present and should undergo thermal depolymerization by unzipping from these poorly thermostable end-groups.…”
Section: Thermal Degradation Kineticsmentioning
confidence: 81%
“…[ 32 ]. Besides, if PVDF is synthesized from the persulfate initiator (emulsion process) [ 19 , 20 ], sulfate end-groups are present and should undergo thermal depolymerization by unzipping from these poorly thermostable end-groups. Figure 5 Reconstruction of the mechanism of H–F elimination followed by polyaromatization of PVDF during its thermal degradation.…”
Section: Resultsmentioning
confidence: 99%
“…The nonpolar α -form PVDF has its use well consolidated in structural applications such as flexible pipes for oil and gas exploration [ 11 , 12 , 13 , 14 ]. PVDF can also be employed as a liner (coating) or inner layer in multilayers thermoplastic pipes or storage tanks dedicated to storage and/or transportation of biofuels, mixtures of biofuels-gasoline and sodium hydroxide solutions (except in critical conditions, i.e., temperature range from 50 to 90 °C and pH of 13.5–14), among others [ 5 , 7 , 13 , 15 , 16 , 17 , 18 , 19 , 20 ]. Additionally, PVDF has several other industrial uses, including valves, membrane filters, pumps and bearings, chemicals and pharmaceuticals packaging, and barrier for gaseous substances [ 7 , 8 , 19 , 21 ].…”
PVDF was prepared by compression molding, and its phase content/structure was assessed by WAXD, DSC, and FTIR-ATR spectroscopy. Next, PVDF samples were aged in bioethanol fuel at 60 °C or annealed in the same temperature by 30 ─ 180 days. Then, the influence of aging/annealing on thermal stability, thermal degradation kinetics, and lifetime of the PVDF was investigated by thermogravimetric analysis (TGA/DTG), as well as the structure was again examined. The crystallinity of ~41% (from WAXD) or ~49% (from DSC) were identified for unaged PVDF, without significant changes after aging or annealing. This PVDF presented not only one phase, but a mixture of
α
-,
β
- and
γ
-phases,
α
- and
β
-phases with more highlighted vibrational bands. Thermal degradation kinetics was evaluated using the non-isothermal Ozawa–Flynn–Wall method. The activation energy (
E
a
) of thermal degradation was calculated for conversion levels of
α
= 5 ─ 50% at constant heating rates (5, 10, 20, and 40 °C min
─1
),
α
= 10% was fixed for lifetime estimation. The results indicated that temperature alone does not affect the material, but its combination with bioethanol reduced the onset temperature and
E
a
of primary thermal degradation. Additionally, the material lifetime decreased until about five decades (
T
f
= 25 °C and 90 days of exposition) due to the fluid effect after aging.
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