Process for reducing fogging from high melt strength polypropylene

Abstract

Process for reducing fogging from high melt strength polypropylene (HMS-PP) obtained by heat treating polypropylene at a temperature between 150 C. and 300 C. in the presence of a dialkyl peroxydicarbonate, said process involving the introduction of an anhydride to said high melt strength polypropylene.

Claims

1. A process for reducing fogging from high melt strength polypropylene (HMS-PP), the process comprising a step of heat treating polypropylene at a temperature between 150 C. and 300 C. in the presence of a dialkyl peroxydicarbonate to obtain a high melt strength polypropylene, introducing an anhydride into the high melt strength polypropylene, and carrying out a fogging analysis on the high melt strength polypropylene after introduction of the anhydride into the high melt strength polypropylene, wherein the anhydride is selected from the group consisting of bisanhydrides, oligoanhydrides, and mono-anhydrides of formula (I), ##STR00004## wherein R.sup.1 is selected from hydrogen and saturated, unsaturated, linear, branched, or cyclic hydrocarbon chains with 2 to 30 carbon atoms, optionally substituted with oxygen-containing groups, R.sup.2 is selected from hydrogen and saturated, unsaturated, linear, branched, or cyclic hydrocarbon chains with 2 to 30 carbon atoms, optionally substituted with oxygen-containing groups, R.sup.3 is selected from hydrogen, hydroxyl groups, and saturated, linear, branched, and/or cyclic hydrocarbon chains with 2 to 30 carbon atoms, optionally substituted with oxygen-containing groups, R.sup.1 and R.sup.2 or R.sup.1 and R.sup.3 can be connected to form a saturated aliphatic ring or a saturated heterocyclic ring; and n=1.

2. A process for enhancing the melt strength of polypropylene, comprising heat treating the polypropylene at a temperature between 150 C. and 300 C. in the presence of 0.3-3 wt %, based on the weight of the polypropylene, of a dialkyl peroxydicarbonate, and introducing an anhydride into the polypropylene before or during said heat treatment, in a molar ratio anhydride functionalities/dialkyl peroxydicarbonate in the range 0.8-3.6, said anhydride being selected from the group consisting of mono-anhydrides of formula (I), bisanhydrides, and oligo-anhydrides, ##STR00005## wherein R.sup.1 is selected from hydrogen and saturated, linear, branched, or cyclic hydrocarbon chains with 2 to 30 carbon atoms, optionally substituted with oxygen-containing groups, R.sup.2 is selected from hydrogen and saturated, unsaturated, linear, branched, or cyclic hydrocarbon chains with 2 to 30 carbon atoms, optionally substituted with oxygen-containing groups, R.sup.3 is selected from hydrogen, hydroxyl groups, and saturated linear, branched, and/or cyclic hydrocarbon chains with 2 to 30 carbon atoms, optionally substituted with oxygen-containing groups, R.sup.1 and R.sup.2 or R.sup.1 and R.sup.3 can be connected to form a saturated aliphatic ring or a saturated heterocyclic ring; and n=1, wherein the anhydride is formed in-situ from a corresponding polycarboxylic acid, said process requiring the addition of the polycarboxylic acid to the polypropylene before or during said heat treating, and wherein the polycarboxylic acid is selected from the group consisting of citric acid; phthalic acid; succinic acid; and succinic acid-modified polyolefins/oligomers.

3. The process according to claim 1 wherein R.sup.1 and R.sup.3 are hydrogen.

4. The process according to claim 3 wherein R.sup.2 is an unsaturated hydrocarbon chain and the anhydride does not graft into the polypropylene.

5. The process according to claim 4 wherein the anhydride is an alkenyl succinic anhydride (ASA).

6. The process according to claim 5 wherein the ASA has an alkenyl chain with 6 to 24 carbon atoms.

7. The process according to claim 6 wherein the alkenyl chain has 8 to 18 carbon atoms.

8. The process according to claim 1 wherein the anhydride is formed in-situ from the corresponding polycarboxylic acid, said process requiring the addition of said polycarboxylic acid to the high melt strength polypropylene, which is then subjected to a further heat treatment.

9. The process according to claim 2 wherein a molar ratio anhydride functionalities/dialkyl peroxydicarbonate is in the range 1.2-2.5.

10. The process according to claim 1 wherein the dialkyl peroxydicarbonate is dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate, or di(4-tert-butylcyclohexyl) peroxydicarbonate.

11. The process according to claim 1 wherein the anhydride is selected from the group consisting of n-octenyl succinic anhydride; n-dodecenyl succinic anhydride; tetrapropenyl succinic anhydride; n-octadecenyl succinic anhydride; i-octadecenyl succinic; i-hexadecenyl succinic anhydride; octadecenyl succinic anhydride and any mixtures thereof.

12. The process according to claim 1 wherein the step of heat treating is performed at a temperature between 160 C. and 240 C.

13. The process according to claim 2 wherein the step of heat treating is performed at a temperature between 160 C. and 240 C.

14. The process according to claim 8 wherein the polycarboxylic acid is selected from the group consisting of citric acid; phthalic acid; succinic acid; and succinic acid-modified polyolefins/oligomers.

15. The process according to claim 2 wherein the dialkyl peroxydicarbonate is dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate, or di(4-tert-butylcyclohexyl) peroxydicarbonate.

16. A high melt strength polypropylene formed from the process of claim 1.

17. A polypropylene formed from the process of claim 2.

Description

EXAMPLES

Fogging Analysis

(1) Fogging analysis (FOG) was carried out according to automotive method VDA 278 (Verband der Automobilindustrie e.V., Berlin, October 2011). This standard method involves dynamic headspace GC analysis.

(2) In order to determine VOC, i.e. volatile organic compounds, a sample was heated to 90 C. during 30 minutes in a glass desorption tube under helium purge.

(3) After VOC analysis, the same desorption tube was heated to 120 C. during 60 minutes under helium purge, in order to determine FOG, i.e. FOGging organic compounds. The released volatiles were accumulated on a cold trap. After desorption, the trap was rapidly heated and the components were transferred to a GC column for analysis. An FID (flame ionization) detector was used for quantification of the FOG value; an MSD (mass spectrometry) detector was used to identify the relevant eluted organic compounds (in the boiling range of n-alkanes with chain length C14 to C32).

(4) For the FOG value, the amount of volatiles was calculated using the response factor of hexadecane. The contribution of all organic compounds in the boiling range of n-alkanes with chain length C14 to C32 were added up (the retention time range was 12.3 to 40 minutes for the Examples given in Table 2).

(5) The relative decrease of the FOG value as a result of the presence of reactive additive is given as % FOG reduction.

Melt Flow Index

(6) The melt flow index (MFI) was measured with a Goettfert Melt Indexer MI-3 according to ISO 1133 (230 C./2.16 kg load). The MFI is expressed in g/10 min.

Melt Strength

(7) The melt strength (MS) was measured (in cN) with a Goettfert Rheograph 20 (capillary rheometer) in combination with a Goettfert Rheotens 71.97, according to the manufacturer's instructions using the following configuration and settings: Rheograph: Temperature: 220 C. Melting time: 10 minutes Die: capillary, length 30 mm, diameter 2 mm Barrel chamber and piston: diameter 15 mm Piston speed: 0.32 mm/s, corresponding to a shear rate of 72 s.sup.1 Melt strand speed (at start): 20 mm/s Rheotens: Acceleration of wheels (strand): 10 mm/s.sup.2 Barrel to mid-wheel distance: 100 mm Strand length: 70 mm

NMR Analysis

(8) Spectra were recorded on a Bruker Avance-III 600 NMR spectrometer with a proton resonance frequency of 600 MHz and a carbon resonance frequency of 150 MHz. The proton NMR spectra were calibrated using the TMS present in the NMR solvent at 0.0 ppm. The carbon NMR spectra were calibrated using the CDCl.sub.3 solvent peak at 77.1 ppm.

(9) TABLE-US-00001 TABLE 1 NMR Spectrometer and acquisition details Spectrometer and Acquisition details Probe 5 mm BBO ATM probe and z-gradient feature Tube type 5 mm disposable NMR tube for Bruker SampleJet Operating 300 Kelvin temperature .sup.1H-NMR .sup.13C-NMR Operating 600 MHz 150 MHz frequency pulse program zg30 zgpg30 (power gated) Relaxation delay 5 sec. 2 sec. Pulse 30 degrees 30 degrees Time domain (TD) 64k 64k Acquisition time 2.66 sec. 0.91 sec. Spectrum width 20 ppm 240 ppm Number of scans 640 1024 Dummy scans 2 2 Processing parameters data size (SI) 64k 64k Line broadening 0.3 Hz 3 Hz ME_mod no no NCOEF 0 0 Solvent used: CDCl.sub.3

Extraction Procedure

(10) An accurate amount of 1 g of the HMS-PP granules was extracted with an accurate amount of 10 g deuterated chloroform for 72 hours at room temperature. 1 ml of this chloroform extract solution was then transferred into a 5 mm NMR tube and the .sup.1H-NMR spectrum was recorded applying the conditions listed in Table 1.

(11) The HMS-PP granules were extracted for a second time in the same way. Results for both extracts were combined.

(12) The digital ERETIC method was applied to enable quantification of the samples. In brief, this method calculates a sensitivity factor from the calibration of a known molar concentration of NMR standard, and applies it to the unknown sample spectrum. This allows the molar concentration of the unknown sample to be quantified.

Extrusion

(13) 500 g of polypropylene homopolymer (PP) powder, 10 g (2 phr) dicetyl peroxydicarbonate (Perkadox 24L), 0.5 g (0.1 phr) Irganox 1010 antioxidant, and the respective amounts of reactive additive (see Table 2) were mixed in a bucket with a spatula, and subsequently on a bucket mixer for 10 min.

(14) Reactive additives that were difficult to homogeneously distribute (like waxy solids) were first dissolved in 20 ml dichloromethane or acetone, and drop wise added to the 500 g PP powder (containing 0.5 g Irganox 1010) in the bucket and mixed well with a spatula. The solvent was then allowed to evaporate in a fumehood for 4 hours.

(15) Dicetyl peroxydicarbonate (Perkadox 24L, ex-AkzoNobel) was then added and mixed well with a spatula, after which the complete composition was mixed with a bucket mixer for 10 min.

(16) The compounds were extruded on a Haake PolyLab OS RheoDrive 7 system fitted with a Haake Rheomex OS PTW16 extruder (co-rotating twin-screw, L/D=40), from Thermo Scientific, using following settings: Temperature profile settings: hopper at 30 C., zone 1 at 160 C., zones 2-4 at 190 C., zones 5-6 at 200 C., zones 7-10 at 210 C. Screw speed: 280 rpm. Throughput: 1.4 kg/h, dosed by a Brabender gravimetric screw feeder type DDW-MD2-DSR28-10. Nitrogen was purged at the hopper (3.5 L/min) and the die (9 L/min).

(17) The extruded material was led through a water bath for cooling and the cooled strands were granulated by an automatic granulator.

(18) The extruded HMS-PP compounds (wet samples) were analysed for fogging reduction.

(19) One sample was analysed for fogging after drying at 60 C. for 16 hours in a circulation oven in order to mimic drying in a silo on industrial scale.

(20) Another sample was extruded without peroxide, but in the presence of citric acid and cetyl alcohol.

(21) Before measuring MFI and MS, the samples were dried at 60 C. for 16 hours in a circulation oven.

(22) The results are displayed in Table 2.

(23) The blank PP sample in Table 2 refers to untreated polypropylene mixed with 0.1 phr Irganox 1010 only.

(24) That cetyl alcohol, formed upon decomposition of the peroxide, is the (major) cause of fogging is confirmed by experiment 3, which shows similar FOG reduction as the same experiment in which cetyl alcohol was replaced with dicetyl peroxydicarbonate (38% vs. 41%).

(25) Table 2 further shows that fogging can be reduced effectively using the reactive additivesi.e. anhydrides according to the invention and acids which form such anhydrides in situ.

(26) The presence of reactive additive did not negatively influence the performance of the peroxydicarbonate used: good melt flow indeces and melt strengths were obtained in the presence of the reactive additive.

(27) TABLE-US-00002 TABLE 2 Results of HMS-PP treated with various reactive polycarboxylic acids and (polymeric) anhydrides Per- FOG MFI oxide Reactive additive reduc- (g/10 MS Exp. ? type & amount tion (%) min) (cN) PP 12.1 0.5 blank 1 yes 0 5.3 9-10 2 yes 1.11 phr Citric acid 41 5.3 n.m. 3 no 1.2 phr Cetyl alcohol + 38 11.9 n.m. 1.11 phr Citric acid 4 yes 0.96 phr Phthalic acid 51 5.0 n.m. 5 yes 0.68 phr Succinic acid 53 7.3 n.m. 6 yes 0.86 phr Phthalic anhydride 58 5.1 7-7.5 7 yes 0.88 phr 4-Cyclohexene-1,2- 40 4.0 n.m. dicarboxylic anhydride 8 yes 1.54 phr ASA Eka SA220* 63 5.3 9.5-10 9 yes 1.54 phr ASA Eka SA220* (1) 74 n.m. n.m. 10 yes 15 phr Kayabrid 006PP* 53 8.6 n.m. 11 yes 1.21 phr ASA C8 linear* 88 5.3 8.5-9.5 12 yes 1.54 phr ASA C12 linear* 90 5.6 8.5-9 13 yes 1.54 phr ASA C12 branched* 67 5.9 8-9 n.m. = not measured *ASA C8 linear: n-octenyl succinic anhydride (OSA), from Milliken ASA C12 linear: n-dodecenyl succinic anhydride (DDSA), from Aldrich ASA C12 branched: tetrapropenyl succinic anhydride (TPSA), from Milliken ASA Eka SA220: C16/C18 alkenyl succinic anhydride, from Eka Nobel Kayabrid 006PP: maleic anhydride grafted polypropylene, from AkzoNobel (1) dried sample analyzed for FOG reduction

(28) The samples of Experiments 1, 6, 11, and 12 were subjected to the above-described extraction procedure. The results are displayed in Table 3.

(29) The extractable amounts of cetyl alcohol (C16-OH) and monoester(s)formed by reaction between cetyl alcohol and anhydrideconfirm that the anhydrides did not graft on PP.

(30) These experiments also confirm the formation of monoester(s) of cetyl alcohol and anhydride.

(31) TABLE-US-00003 TABLE 3 NMR results of (deuterated) chloroform extractable monoesters, cetyl alcohol, and anhydride (in wt %) Reactive additive Monoester(s) C16OH anhydride 1.21 phr ASA C8 linear* 2.5 0.2 <0.1 1.54 phr ASA C12 linear* 2.8 0.1 <0.1 0.86 phr Phthalic anhydride 1.7 0.4 <0.1 none none 1.3 none