Fuel tank composition

Abstract

The present invention proposes a fuel tank comprising at least two shells weldable together, each of said at least two shells is made of a polymer composition comprising at least 45% by weight of at least one aromatic polyamide and at least 10% by weight of at least one aliphatic polyamide relative to the total weight of the polymer composition.

Claims

1. A fuel tank comprising at least two shells weldable together, each of said at least two shells is made of a polymer composition comprising at least 45% by weight of at least one aromatic polyamide and at least 10% by weight of at least one aliphatic polyamide relative to the total weight of the polymer composition, the maximum content of aromatic group-containing repeating units in an aliphatic polyamide being 0 mole % based on 100 mole % repeating units in the aliphatic polyamide polymer, wherein the at least one aromatic polyamide is a polyphtalamide (PPA).

2. The fuel tank according to claim 1, wherein the weight ratio between the at least one aromatic polyamide and the at least one aliphatic polyamide is comprised between 1.4 and 9.

3. The fuel tank according to claim 1, wherein the polymer composition comprises: at least one first composition of aromatic polyamide in a first proportion of from 65 to 90% by weight relative to the total weight of the polymer composition, said first proportion being measured by NMR spectroscopy; and at least one second composition of aliphatic polyamide in a second proportion of from 10 to 35% by weight relative to the total weight of the polymer composition, said second proportion being measured by NMR spectroscopy.

4. The fuel tank according to claim 3, wherein the first proportion is from 75 to 80% by weight relative to the total weight of the polymer composition and the second proportion is from 20 to 25% by weight relative to the total weight of the polymer composition.

5. The fuel tank according to claim 3, wherein said first composition further comprises a first modifying agent, and wherein the proportion of aromatic polyamide is from 60 to 100% by weight relative to the total weight of said first composition, and the proportion of first modifying agent is from 0 to 40% by weight relative to the total weight of said first composition.

6. The fuel tank according to claim 3, wherein said second composition further comprises a second modifying agent, and wherein the proportion of aliphatic polyamide is from 60 to 100% by weight relative to the total weight of said second composition, and the proportion of second modifying agent is from 0 to 40% by weight relative to the total weight of said second composition.

7. The fuel tank according to claim 1, wherein the at least one aliphatic polyamide is a PA6 or/and PA6.6.

8. The fuel tank according to claim 1, wherein the polymer composition is substantially devoid of agents adversely affecting the fuel permeability.

9. A vehicle containing a fuel tank according to claim 1.

Description

DETAILED DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a DSC Thermogram for the polymer composition of in the examples. Specifically, FIG. 1 represents the DSC spectrum of the polymer composition comprising 45% by weight of PPA and 30% by weight of PA and 24.5% by weight of modifying agent and 0.5% by weight of carbon 25 black. The DSC spectrum presents a crystallization exotherm with an onset at about 254° C. That means that the crystallization starts at 254° C. during the cooling during the DSC test.

(2) FIG. 2A is the entire .sup.13C NMR spectrum of the polymer composition. FIG. 2B is a zoomed part of the .sup.13C NMR spectrum of the polymer composition highlighting the characteristic peaks of the polymer composition (such as peaks corresponding to carbon of IPA carbonyl, carbon of TA carbonyl, carbon of PA6 carbonyl, carbon of PA6.6 carbonyl).

(3) FIG. 3 illustrates the TEM image obtained for ultra-thin layers (70 nm) for observation by Transmission Electron Microscopy were made using an ultra-microtome brand Leica Reichert-UMUC6 at room temperature from samples taken from the plates and more particularly from the core of the plates. The observations were made using a Zeiss LEO922 with an acceleration voltage of 120 kV.

(4) FIG. 4A illustrates an Atomic Force Microscopy image of the polymer composition of the examples. FIG. 4B shows a histogram of the distribution of elasticity modulus values of the blend PPA/PA.

EXPERIMENTAL PART

(5) Preparation of the Polymer Composition

(6) The polymer composition is preferably prepared by extrusion. The materials from the polymer composition are introduced in the hopper of the extruder thanks to a feeding device according to desired proportions. A twin screw extruder is preferred. The process is thus a melt mixing process. The materials are dried before mixing if needed. At the exit of the extruder, the material is cool down (in the air or through a water bath).

(7) The material is then dried and finally pelletized and packaged in sealed bags. Additional drying operations can also be performed after the material has been pelletized. The pellets obtained are then used to prepare the half shells by injection molding.

Experimental Examples

(8) The following examples are considered to be non-limiting and only representative of selected embodiments.

(9) Mechanical Tests

(10) The mechanical performance was tested by determining the tensile modulus according to the norm ISO 527 at 1 mm/min. ISO527-1BA test specimens are machined on injection molded test plates or tank shells. The thickness of the test specimens is 3 mm. Test specimens are conditioned at least 2 days at 23° C. and 50% relative humidity before testing. After installation on the machine, test specimens are conditioned during 15 min at the desired temperature. Stress/strain curve is recorded.

(11) The tensile modulus results of different polymer compositions according the invention are presented in the following Table (page 16).

(12) Fuel Permeability Tests

(13) Fuel permeability tests were performed to study the chemical performance of different polymer compositions according to the invention.

(14) The term “fuel” is here understood as comprising various mixtures of hydrocarbons used as fuel in internal combustion or high-compression engines. Thus, this term in particular encompasses fuel oil, diesel oil and all categories of petrol, as well as mixtures of hydrocarbons and alcohols, or the like. The fuel permeability (FP) was measured by the gas chromatography method. The fuel used is “ASTM fuel CE10” (composed of 10 vol. % ethanol and 90 vol. % of “ASTM fuel C” (50/50 wt % mixture of toluene and iso-octane)). The fuel permeability measurements were performed at 40° C. under dry conditions. The samples are conditioned with fuel during at least 10 weeks to reach a steady-state. The standard deviation in this method is between 5 and 10%. Test samples for permeability are injection molded plates with a thickness of 3 mm. These plates are mounted on a metal cell. The surface of the sample exposed to fuel is a disk of 80 mm diameter. A rubber seal is placed between the sample and the metal cell. In order to avoid hydrocarbon emissions from the seal, the permeability measure is performed with double cells.

(15) The fuel permeability results of different polymer compositions according to the invention are presented in the following Table (page 16).

(16) Welding Performance Tests

(17) Differential scanning calorimetry (DSC) has been used to study the thermal properties, degree of crystallinity of different polymer compositions and more particularly to study the welding performance of different polymer compositions according to the invention.

(18) The result of a DSC measurement using a Differential Scanning calorimeter is a curve of heat flux versus temperature. DSC is used to determine specific temperatures such as crystallization temperature (Tc).

(19) The DSC thermograms were produced. For each analysis, approximately 10 mg of the polymer composition was placed in aluminum pan and sealed. The sample pan was placed into the DSC instrument with an empty aluminum pan as its reference. Then, different polymer composition samples were heated using a ramp program from −50 to 350° C. at 10° C./min.

(20) The DSC result values are reported in the following Table.

(21) One example of DSC Thermogram for the polymer composition is shown in FIG. 1.

(22) TABLE-US-00001 100 wt % of first 80 wt % of first 75 wt % of first 70 wt % of first 65 wt % of first 40 wt % of first composition composition composition composition composition 45% wt of PPA composition of PPA of PPA of PPA of PPA of PPA 30% wt of PA of PPA 0% of second 20% of second 25% of second 30% of second 25% of second 24.5% of 60% of second Polymer composition composition composition composition composition modifying agents composition composition of PA6 of PA6 of PA6 of PA6 of PA6 0.5% carbon black of PA6 Tensile Modulus 1521 1374 1200 600 500 280 <280 TM (60° C.) MPa Fuel Permeability FP <10 <10  <10 <10 <10 <10 / mg mm/(m.sup.2 .Math. day) Crystallization 267 259 / 248 / 254 223 and 157 temperature Tc ° C. Transfer time reference 0.32 more / 0.72 more / / / gain s compared to compared to reference reference

(23) The Table illustrates the mechanical and chemical properties of the polymer composition of the invention.

(24) In the interval of the invention, the polymer compositions present good results in term of mechanical property. The tensile modulus at 60° C. is above 280 MPa. These results are particularly true for a polymer composition comprising 80% by weight of the first composition of PPA and 20% by weight of the second composition of PA6, these contents being relative to the total weight of the polymer composition.

(25) Regarding to the chemical properties, the polymer compositions of the invention present good fuel permeability, inferior than 10 mg.Math.mm/(m.sup.2.Math.day) and present crystallization temperatures delayed compared to a composition of a neat PPA. Those have a positive impact of the transfer time for the welding operation. The transfer time for the welding operation is increased, facilitating thus the welding operation between two different parts of the fuel tank, these two parts having the polymer composition of the invention.

(26) In regards to the mechanical and chemical properties, the polymer composition comprising a content of the first composition of PPA of 80% by weight and a content of the second composition of PA6 of 20% by weight relative to the total weight of the polymer composition is the polymer composition which best meets the technical objectives.

(27) Another particular advantage of the polymer composition of the invention is the ability to manufacture different tanks withstanding different pressure levels; for example an unpressurized tank which comprises a polymer composition having 45% by weight of PPA and, on the contrary, a pressurized tank withstanding more than 300 mbar which comprises a polymer composition having 75% by weight of the first composition of PPA.

(28) Characterization of the Polymer Composition

(29) DSC Description

(30) FIG. 1 represents the DSC spectrum of the polymer composition comprising 45% by weight of PPA and 30% by weight of PA and 24.5% by weight of modifying agent and 0.5% by weight of carbon black.

(31) The DSC spectrum presents a crystallization exotherm with an onset at about 254° C. That means that the crystallization starts at 254° C. during the cooling during the DSC test.

(32) NMR Description

(33) The polymer composition according to the invention was characterized by NMR spectroscopy.

(34) Polyamides may be produced by the reaction of a difunctional acid with a difunctional amine, or the self-condensation of either an amino acid or a lactam.

(35) By definition, aromatic polyamides are polymers comprising at least one repeating units of “type 1” having at least one CONH group in the polymer chain and at least one aromatic group. Although not required, such aromatic groups typically originate in a diacid monomer, and include terephthalic acid (TA), isophthalic acid (IPA), phthalic acid, dodecanedioic acid etc.

(36) The diacid and the diamine monomers form characteristic repeating structural units of the polymer chain.

(37) By identifying these repeating units, it is possible to determine the nature of the diacid and the diamine and consequently it is possible to determine the nature of the polymer.

(38) A convenient way to identify these repeating units is to analyze the chemical functions on each carbon of these repeating units by carbon 13 NMR.

(39) In a first qualitative step, the chemical functions present in the mixture are identified. The chemical shifts corresponding to the different functions are available in reference tables or handbooks. The 1H NMR spectra brings complementary information, as disclosed for instance in J. Am. Chem. Soc. 1956, 78, 3043.

(40) Thanks to carbon 13 NMR, it is possible to determine the relative position of these functions, one to the others. Indeed, the chemical shift of a given carbon, obtained by carbon 13 NMR, is influenced by the chemical functions of the next carbons of the polymer chains.

(41) After this step, chemical functions on each adjacent carbon are known, allowing to determine the whole polymeric chain which is present. The chemical function associated to each peak is determined.

(42) A second quantitative step is based on integration of each peak.

(43) FIG. 2A is the entire 13C NMR spectrum of the polymer composition. FIG. 2B is a zoomed part of the 13C NMR spectrum of the polymer composition highlighting the characteristic peaks of the polymer composition (such as peaks corresponding to carbon of IPA carbonyl, carbon of TA carbonyl, carbon of PA6 carbonyl, carbon of PA6.6 carbonyl).

(44) The 13C NMR spectrum were acquired in a 30/70 volume mix of trifluoroacetic anhydride (C4F6O3) and deuterated chloroform (CDCl3) at room temperature and auto referenced against the solvent peak using the JEOL ECS 400 NMR spectrometer.

(45) The chemical shifts δ are in units of part per million (ppm). With the 13C NMR spectrum and its corresponding NMR table, the identification of carbons of the expected chemical groups: IPA carbonyl, TA carbonyl, PA6 carbonyl, PA6.6 carbonyl can be performed. (IPA: isophthalic acid, TA: terephthalic acid)

(46) The chemical group identification is reported in the following Table. The integration of these carbons is given by the spectrum.

(47) TA, IPA and PA66 have 2 carbon (2 carbonyl functions) exhibiting the same chemical shift.

(48) PA6 has only one associated carbon (one carbonyl function)

(49) TABLE-US-00002 Molecule Number of carbons Integration Chemical shift (ppm) IPA carbonyl 2 0.45 171.84 TA carbonyl 2 1.04 172.03 PA6 carbonyl 1 1 177.64 PA6.6 carbonyl 2 0.29 177.37

(50) Furthermore, the total of carbonyl functions is 100%.

(51) With these results, the molar proportion of PA6, PA6.6, TA and IPA can be determined by the following equations:

(52) $\mathrm{TA}+\mathrm{IPA}+2\mathrm{PA}6+\mathrm{PA}6.6=100$$\frac{\mathrm{TA}}{\mathrm{IPA}}=2.3$$\frac{\mathrm{TA}}{\mathrm{PA}6.6}=3.6$$\frac{\mathrm{PA}}{\mathrm{PA}6.6}=6.9$

(53) After calculation, the following molar percentage of the different components of the polymer composition are obtained and reported in the following table:

(54) TABLE-US-00003 components % molar PA6 52.8 PA6.6 7.6 IPA 27.5 TA 11.9 Sum 100

(55) The corresponding weight percentage can be determined and are reported in the following table:

(56) TABLE-US-00004 Molar mass Components g/mol Mass g Weight % PA6 113 5967.7 34.3% PA6.6 226 1729.7 9.9% TA 246 6778.3 38.9% IPA 246 2947.0 16.9% Sum 17422.9

(57) By this analysis, the weight proportion of PPA, PA6, PA6.6, IPA, TA of the polymer composition is determined.

(58) Method for Detecting Modifying Agents in the Polymer Composition:

(59) Transmission Electron Microscopy (TEM)

(60) The morphological characterization of the modifying agents in the polymer composition of the invention was performed by Transmission Electron Microscopy (TEM).

(61) The ultra-thin layers (70 nm) for observation by Transmission Electron Microscopy were made using an ultra-microtome brand Leica Reichert-UMUC6 at room temperature from samples taken from the plates and more particularly from the core of the plates. The observations were made using a Zeiss LEO922 with an acceleration voltage of 120 kV.

(62) In addition, a marking to the vapor of Ruthenium (RuO4) for a period of 12 minutes has been performed on the samples.

(63) FIG. 3 illustrates the TEM image obtained.

(64) Two levels of grey/black are visible in the TEM image. The black phase corresponds to an amorphous phase. That is to say that it corresponds to the modifying agents of the polymer composition.

(65) The grey phase corresponds to the neat PPA.

(66) The light phase (white) corresponds to PA6 (continuous phase).

(67) Atomic Force Microscopy:

(68) AFM measurements were performed with the Peak-Force-QNM fashion installed on a system-Dimension Icon Bruker. This mode provides the surface topography and the value of elastic modulus surface simultaneously. The AFM tips with a constant spring of ˜40 N/m and a tip radius of curvature of ˜15 nm were used to image the sample surface. Flat surfaces having a roughness at the nanoscale were prepared with a diamond knife and with an ultra-cryo-microtome technique. The temperature for the preparation was either to room temperature or to −100° C. with a cooling by liquid nitrogen. The cutting temperature selection optimizes the surface quality. Final surfaces prepared by microtomy have a size of 2*2 mm. The raw data were analyzed using the Nanoscope software to obtain topography images, modulus of elasticity and corresponding adhesion strength.

(69) FIG. 4A illustrates the AFM image obtained.

(70) Two levels of grey/black are visible in the AFM image. The dark phase corresponds to an amorphous phase. That is to say that it corresponds to the modifying agents of the polymer composition.

(71) The light phase corresponds to a continuous phase corresponding to the blend of the PPA composition and the PA6 composition of the polymer composition (light area) in which is dispersed the dark phase (e.g. modifying agents).

(72) The histogram of the distribution of elasticity modulus values of the blend PPA/PA is shown in FIG. 4B.

(73) The average values of the module of the continuous phase PPA/PA and the dispersed phase is approximately equivalent to 1.5 and 0.5 GPa, respectively.

(74) With these two detection methods (TEM, AFM), the proportion of modifying agents are determined by microscopy image analysis.