|Title of Invention||
POLYPROPYLENE-ETHYLENE OCTENE COPOLYMER BLEND NANOCOMPOSITE WITH IMPROVED MECHANICAL PROPERTIES AND THERMAL STABILITY THEREOF
|Abstract||The present invention relates to melt mixing of polypropylene/ethylene octene copolymer blend and intercalated nanofiller organically modified with various quaternary alkyl amine and alkyl ammonium surfactants in presence of MAPP as a compatibilizer to form nanocomposites blend. These nanocomposites blend are found to exhibit significant improved impact strength while retaining the tensile strength and modulus and flexural strength and modulus of PP. Moreover the blend nanocomposite system can desirably improve the thermal stability of PP as well as PP/EOC.|
|Full Text|| DESCRIPTION
This invention relates to nanocomposites from at least one filler of nanometer range which has been organically modified with various quaternary alkyl amine and alkyl ammonium surfactants. These organically modified nanofillers are meltmixed with Polypropylene (PP)-Ethylene octene copolymer (EOC) blend of an optimised ratio of 70:30 in presence of Maleic anhydride grafted polypropylene (MAPP) as compatibiliser; to increase the impact strength while retaining the tensile strength and modulus and flexural strength and modulus of PP. Moreover the blend nanocomposite system can desirably improve the thermal stability of PP as well as PP/EOC.
Nanocomposites are polymer systems containing inorganic filler of nanometer range. Some of these are disclosed in US patent Nos. 6060549, 6103817, 5883173, 5576372, 5576373, 5665185. These materials blend a nanofiller with polymer to produce a composite with better physical and mechanical properties than their conventionally filled counterparts, at a lower nanofiller loading.
Nanofiller used in the polymer nanocomposites is based on the smectite class of aluminium silicate clays, a common representative of which is montmorillonite. Naturally occurring montmorillonite constitutes a 2:1 layered silicate with a central octahedral aluminate structure surrounded on either side with a tetrahedral silicate structure. Iron or magnesium occasionally replaces the aluminium atom rendering an overall negative charge which is counter balanced by the inorganic cations residing between the sheets holding them together. Cation exchange reactions between interlayer inorganic cations and organic cations increases the intergallery spacing in the silicate sheets, improves compatibility between the fillers and the matrix thereby resulting in exfoliation. Although naturally occurring and synthetic variations of this basic mineral structure can be used to prepare nanocomposites, significant property improvements can be achieved by altering the surface chemistry of clays through cation exchange reactions of interlayer inorganic cations such as Na sup. + or Ca sup. + with alkyl amine/ammonium cations.
Property improvement is mainly due to the capability of the layers to expand (intercalate) or to completely separate from each other (exfoliation). This creates an enlarged surface of the filler material and an enlarged boundary surface with the matrix polymer. To achieve intercalation or exfoliation when producing polymer nanocomposites, the nanofillers (layered silicates) are modified by cation exchange with organic compounds and thus made organophilic. They are also referred to as organoclays. Exfoliated structure of the organoclay provides large surface area with high aspect ratio of the order of 50 to 2000. This results in significant improvement in strength and modulus in polymers.
Working organically intercalated nanofillers into polymers by in-situ polymerization or melt compounding has been described in several patent documents and is mostly associated with an improvement of the mechanical and barrier properties as well as thermal stability [U.S. Pat. No. 4,739,007, WO0034180].
Polypropylene nanocomposites offer a combination of inexpensive price, easy processibility and wide spectrum of properties. However, its high notch sensitivity, fracture toughness have been a major limiting factor. Compounding of PP with a dispersed elastomeric phase i.e. ethylene propylene diene monomer(EPDM) , metallocene catalysed polyethylene elastomer has been commonly used to alter stress distribution and control crack propagation and termination. However, the other properties viz. tensile strength and modulus, flexural strength and modulus decreases significantly. The present report purportedly reports a fabrication/preparation of a polyolefin blend nanocomposite using various organically modified nanofillers. This document also reports the improved impact strength of PP in a nanocomposites blend while retaining the other mechanical properties viz. tensile strength its modulus and flexural strength its modulus in the system. Additionally the study also reflects enhanced thermal stability in the blends with the incorporation of organically modified nanofillers.
In an embodiment, a nanocomposite blend is formed that includes polypropylene blended with an elastomer and at least one nanofiller material modified with an organic surfactant, wherein the polymeric material(s) is compatible with the modified nanofiller material and an external compatibilizing agent. The nanocomposite material advantageously exhibits enhanced physical, mechanical and thermal properties as compared with the blend system.
FIG. 1 illustrates the izod impact strength of an isotactic polypropylene (PP) filled with an ethylene octene copolymer (EOC). FIG. 2 illustrates the tensile strength and modulus. FIG. 3 illustrates the flexural Strength and modulus FIG. 4 illustrates the izod impact strength of PP/EOC blend filled with organically modified nanofillers. FIG. 5 a, b illustrates the tensile strength and modulus. FIG. 6 a, b illustrates the flexural Strength and modulus FIG. 7 a, b, c, d illustrates the TEM micrographs of nanocomposite blends prepared using various organically modified clays (OMMT-I, Cloisite 20A, Cloisite 30 B, OMMT-II) FIG. 8 a, b displays the WAXD patterns of all the nanoclays and nanocomposites blends. FIG. 9 DSC melting endotherms of PP, PP/EOC blend and the nanocomposites blend. FIG. 10 DSC cooling exotherms of PP, PP/EOC blend and the nanocomposites blend. FIG. 11 TGA thermograms of PP, PP/EOC blend and the nanocomposites blend. The actual data for FIGS. 1, 2, 3, 4, 5, 6, 9, 10 and 11 are in Tables I through IV.
The nanosize fillers can be generally any filler or combination of fillers having at least one
dimension (length, width, or thickness) from 1 to about 30 nanometers. For the purpose of this disclosure the dimension is that of the filler dispersed in a continuous matrix, for example clays which can be broken down into very thin constituent layers (platelets) when dispersed in a molten polyolefin under shear.
The present inventors worked to develop a method of improving the mechanical strength and thermal stability of a nanocomposite blend. In doing so, we found that a nanocomposite prepared by exfoliating intercalated clay in a PP blend matrix having high impact strength, such as PP/EPDM, PP blended with a metaliocene catalysed polyethylene elastomer, increases the impact strength and notch sensitivity of PP while retaining its tensile and flexural properties. It is also found that a nanocomposite blend comprising PP matrix, a metaliocene catalysed polyethylene elastomer, an organically modified nanofiller and a compatibilizer has superior thermal stability.
The nanocomposite blend composition of the present invention is characterized by comprising a PP matrix resin (a); an intercalated nanoclay from one or more materials selected from i) montmorillonite, bentonite, kaolinite, mica, hectorite, fluorohectorite, saponite, beidelite, nontronite, stevensite, vermiculite, hallosite, volkonskoite, suconite, magadite, and kenyalite; ii) the organic material preferably having a functional group selected from quaternary alkyl ammonium, phosphonium, maleate, succinate, acrylate, benzylic hydrogen, a quaternary alkyl amine (b), a metaliocene catalysed polyethylene elastomer (c) and compatibilizer (d).
Homopolymers or statistical copolymers or block copolymers of propylene with one or several
olefins such as ethylene and linear and/or branched C.sub.4 to C.sub. 10 1-olefins are used as polypropylenes. It is practical to use polypropylene homopolymers and block copolymers with a low ethylene content
The preferred component a) is a isotactic polypropylene with a melt-flow index of 11g per 10min. (230.degree. C./2.16 kg) and with a density of 0.9 g/ccm
Component b) Intercalated nanofiller
The intercalated clay used in the nanocomposite comprises organic intercalated clay. The organic content of the intercalated clay is preferably 1 to 45 wt %. The nanofiller is a natural sodium montmorillonite, hectorite, bentonite, or synthetic mica with a cation exchange capacity of 60 to 150 mval/100g.
Layered silicates with a cation exchange capacity of at least 50, preferably 60 to 150 mval/100 g
are preferred. The alkaline or earth alkaline metals that can be exchanged in these swellable layered silicates are replaced fully or in part by onium, ammonium, phosphonium, or sulfonium ions in an ion exchange reaction. Swellable layered silicates in which 50 to 200% of the replaceable inorganic cations are replaced by organic cations are particularly preferred.
Cationic nitrogen compounds suitable for intercalation are alkylammonium ions such as lauryl ammonium, myristyl ammonium, palmityl ammonium. Other preferred cationic nitrogen compounds are quaternary ammonium/amine compounds such as distearyldimethyl ammoniumchloride, methyl benzyl di-hydrogenated tallow ammonium chloride, octadecyl amine and dimethyldistearylbenzyl ammoniumchloride.
It is preferred that all nitrogen-containing intercalation components are used in protonated form. All water-soluble organic and inorganic acids are suitable for protonation. Mineral acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, as well as acetic acid, formic acid, oxalic acid, and citric acid are prefered.
Examples of those nanofillers, are sodium montmorillonite, Na-MMT (unmodified having CEC 92.6meq/100g clay), cloisite 20A (modified by 2MBHT: dimethyl, dihydrogenated tallow, quaternary ammonium having CEC of 95meq/100g clay), cloisite 15A (modified by 2MBHT:dimethyl dihydrogenated tallow quaternary ammonium with CEC 125meq/100g clay), cloisite 30B (modified by MT2EtOT methyl, tallow, bis-2-hydroxymethyl, quaternary ammonium and CEC of 90 meq / 100g clay) are commercially available from Southern clay Products Inc, USA.
Component c) Ethylene -octene elastomer
The term "elastomer", as used herein, refers to any polymer or composition of polymers consistent with the ASTM D1566 definition. The term "elastomer" may be used interchangeably with the term "rubber", as used herein. Copolymers of ethylene, and/or propylene and C.sub.1-C.sub.20 olefins derived units such as EOC (ethylene octene copolymer), EP (ethylene propylene rubber) and/or EPDM (ethylene propylene diene monomer rubber) are also contemplated as optional elastomeric components in the nanocomposites of embodiments of our invention. Examples of comonomers in making these copolymers are ethylidene norbomene, vinyl norbornene, dicyclopentadiene, 1-4 hexadiene or dicyclopentadiene. These elastomers are described in RUBBER TECHNOLOGY 260-283 (1995). Suitable ethylene-propylene rubbers or elastomers are commercially available as EXACT.RTM. and VISTALON.RTM. (Exxon Mobil Chemical Company, Houston Tex.). Polyethylene elastomers are formed using well known single-site metallocene catalyst technology, which permits control of comonomer that may be incorporated into the polyethylene polymer and molecular weight distribution. The elastomers are
homopolymers of ethylene, or copolymers of ethylene with higher alpha-olefins having from 3 to 10 carbon atoms such as 1-butene, 1-hexene and 1-octene. The elastomers are commercially available from Dow Plastics, Dow U.S.A., Midland, Mich., under the trademark ENGAGE, especially ENGAGE EG8100 (an ethylene/1-octene copolymer). The ENGAGE elastomers have a density range of 0.865 to 0.889 g/cc and a peak melting point range of 12O.degree. F. to 185.degree. F. Suitable plastomers also are available from ExxonMobil Chemical, under the trademark EXACT. The EXACT elastomers have similar density and peak melting point ranges as defined for the Dow plastomers.
Component d) External Compatibiliser
Among the polar modified materials which can be used in the making of the inventive composite
compounds .is maleated polypropylene. Examples of this maleated polypropylene include Epolene E-43, Epolene G-3015 and Epoiene G-3003 produced by Eastman Chemical Company. These are polypropylene polymers with molecular weight ranging from 15000 g/mol to 50,000 g/mol reacted with maleic anhydride to produce maleated polypropylene containing a maximum of 10 mol percent maleic anhydride. Other suppliers of maleated polypropylene are Uniroyal Chemical company under the name Polybond 3002 and DuPont chemical company under the name Fusabond MD 511D.
Preferably a maleated polyolefin having Blends of Polypropylene (PP) and Ethylene Octene Copolymer (EOC) containing different weight percentage of EOC: 0%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 100% are prepared in a twin screw extruder. The nanocomposites blends are prepared using a) Polypropylene 60 to 70 percent by weight b) nano fillers/layered silicates from 1 to 7 percent by weight, and d) up to 3 percent by weight, preferably from 0.1 to 1.9 percent by weight of maleated polyolefins, of a total of 100 percent by weight and are compounded at temperatures above the melting points of the polymers. Prior to melt mixing the ingredients are dried in a vacuum oven at 60°C for 6 hrs in case of nanoclays & K> hrs for PP & EOC) and then dry-mixed.
The polymer nanocomposite blends according to the invention are particularly suited for use as extrudates, injection-molded parts.
The intercalation components mentioned in the description of component c) act as hydrophobing agents and influence the surface tension of the layered silicates so that polarity and the overall surface energy value drop. This ensures better intermixing and finer dispersion within the
polypropylene phase in the nanocomposite blends as compared to pure PP/EOC nanocomposite
The TEM examination of the PP/EOC nanocomposite blends according to the invention shows fine dispersion of nanofillers within the polypropylene phase. The particles have a size between 0.1 and 1 .mu.m (FIG. 7a). FIG. 7a shows that the exfoliated clay (OMMT-I) are mainly dispersed inside the polypropylene matrix, and accumulation of the layers that form some kind of a card structure around the EOC particles is clearly visible. It is assumed that the interaction between the polypropylene and ethylene octene phases is initiated by the intercalated and delaminated silicate layers. Increased concentration of the organophilic layered silicate at the boundary surface of the polypropylene and EOC phases lowers the surface tension difference between the normally incompatible polymers. A delaminated nanofiller/organically intercalated in the meaning of this invention are swellable layered silicates in which the spacings between the silicate layers are enlarged by the reaction with suitable surfactants/hydrophobing agents.
The nanocomposite blends according to the invention have excellent notch-impact strength while retaining other mechanical properties such as tensile strength and modulus, flexural strength and modulus of the PP/EOC blend matrix.
Compared to pure PP, the impact strength increased up to 455% in the blend nanocomposite prepared using OMMT-I as nanofiller at 5wt% of nanofiller loading. If compared to a polypropylene/EOC blend of the respective composition (70:30), the increase is up to 16% in the OMMT-I nanocomposite blend
The PP/EOC blends according to the invention show a clearly reduced loss in tensile and flexural properties of polypropylene matrix with the incorporation of ethylene octene copolymer. However, the blend nanocomposites show a considerable increase in the impact strength while retaining the other mechanical properties to a significant extent.
In addition to mechanical performance, the thermal stability of the blend matrix as well as PP increased in the nanocomposites blend.
The nanocomposite blend according to the invention has improved performance characteristics and cost effective as follows:
1. Impact resistance and notch sensitivity of PP as well as the blend matrix is improved significantly with the incorporation of organically modified nanofillers.
2. Better-exfoliated structure within the blend matrix was obtained with the use of organic
surfactant methyl benzyl di-hydrogenated tallow ammonium chloride as intercalative agent in
the modification of the nanofiller, Na-MMT over other commercially available clays.
3. Alkyl ammonium intercalation components exhibits improved performance characteristics as
well as improved dispersion over alkyl amine intercalation components
4. The flexural and tensile properties of the PP/EOC blend matrix improved considerably with
the addition of organically modified nanofiller.
5. The thermal stability of PP and the blend matrix are also improved significantly in the
The process for organic treatment of the nanofillers and the invention is explained in greater detail with reference to the examples below, to which however it is not limited:
Naturally occurring Na-MMT was modified in the laboratory using various methods as follows: 5g sample of Na-MMT was dissolved in 95 g distilled water under vigorous stirring condition, to form a uniformly dispersed solution. Subsequently, 3g methyl benzyl di-hydrogenated tallow ammonium chloride (intercalative reagent) was added to the solution, which was then stirred for 1h at 80°C. The dispersed solution was filtered and repeatedly washed with distilled water to remove the excess intercalative reagent, until there was no white precipitate observed when tested in a 0.1 mol/L AgNO3 solution. The product was then vacuum dried to a constant weight and ground into powder (diameter about 40-50 urn) to get the organo montmorillonite. The nanofiller shall be herein designated as OMMT-I
Modification of the Na-MMT using octadecyl amine was carried out using 21gms of MMT dispersed uniformly into hot water (1330 ml/ 80° C) using a mechanical stirrer to obtain a homogenous suspension. Octadecylamine (8.3 g) was dissolved in 670 ml hot water at 80° C with a small amount of HCI for Na+ ion exchange and poured into MMT-water suspension while stirring the solution vigorously. The stirring was continued at a constant temperature of 80° C for 30 min to yield a white precipitate. The resulting white precipitate was filtered and washed three times with distilled water to remove remaining acid and octdecylamine. The MMT intercalated octadecylamine, designated as O-MMT-II was freeze dried and finally ground with a mortar and pestle to obtain particles less than 160 urn.
PP/EOC blends as well as the nanocomposite blends were produced at a L/D ratio of at least 40
using a twin-screw extruder (Haake, Germany). The polymers and layered silicates intercalated with organic substances were added in the first zone using polymer or powder scales. The batch was compounded at temperatures from 180 to 200.degree. C. and a speed of 60 min.sup.-1. The compounded nanocomposite blends were made into test specimens using 80T injection moulding machine (ES330/80HL, ENGEL Austria) as per ASTMD having clamping force 800 kN fitted with a dehumidifier (Bryair, Germany) at a temperature range of 195- 210° C.
The spacing between the silicate sheets was determined by WAXD analysis (WAXD=wide angle X-ray diffraction) using Phillips 'X'Pert MPD, Japan fitted with a diffractometer andrecording accessories employing nitrogen filtered Co Ka radiation (^=0.179 nm) operated at 40 KV. Based on this and on TEM (Transmission Electron Microscopy) recordings, made from a Philips 430t microscope operating at 300 kV, using thin sections prepared by cryo-microtome (Reichert Jung ultra-microtome) at a temperature of 9O.degree.C, conclusions were drawn regarding the degree of exfoliation or dispersion of the nanofillers within the blend matrix.
The mechanical properties of the blends and the nanocomposite blends were examined after conditioning of the specimens at 24 Degree. C and 55% RH. States, using a notch-izod impact strength test (Ceast S.p.A, Italy, Model-P/N 6963) according to ASTMD 256,tensile test according to ASTMD 638 and flexural test as per ASTMD 790 (UTM LR-100K, Lloyd Instrument, UK). Five to seven moulded samples for each formulation were measured to determine the variability at 23. Degree C and 55% RH.
Isotactic PP with a melt-flow index of 11 (230.degree. C./2.16 kg) and density of 0.9 g per ccm were compounded with EOC with a density of 0.86 g per ccm, melt-flow index of 1 (190.degree. C./2.16 kg) and octene content of 25 wt%, at different weight ratios of PP: EOC, 100: 0, 95:5, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80 and 0:100 .
The results are shown in the tables below.
Table I Mechanical Properties of the blends of the invention
PP/EOC Tensile Strength (MPa) S.D. Tensile Modulus (MPa) S.D. Flexural Strength (MPa)) S.D. Flexural Modulus (MPa) S.D. Impact Strength (J/n? S.D.
100:0 19.37 0.56 509.0 0.48 60.71±0.95 0.98 805.9 0.93 114.4 1.00
95:5 17.48 0.71 413.0 0.51 57.08 0.93 781.6+1.2 1.08 120.0 0.97
90:10 14.47 0.85 256 4 0.49 49.42 0.81 687.7 0.83 180.7±1.01 1.08
80:20 13.02 0.83 197.6 0.57 23 46 0.89 560.2 0.89 263.2 1.03
70:30 8.28 0.87 107.0 0.65 14.70 0.82 281.8 0.88 547.0 1.01
60:40 6.32 0.93 96.4 0.69 12.26 0.78 146.6 0.87 419.5 0.96
50:50 5.29 0.97 82.4 0.89 - - 337.6 0.78
40:60 6.72±1.35a 1.12 45.2 1.03 - - 176.7 1.01
30:70 6.47 1.01 12.2± 1.37 1.28 109.5 0.98
20:80 6.07 0.99 5.3 1.11 - - 78.0 0.95
0:100 7.33 0.63 1.7 0.61 - - 0 1.02
The flexural strength & modulus of the blends at 50%,60%,70%,80% loading of EOC virgin EOC could not be
expedited due to higher content of elastomer
a Measurement uncertainty values as for A2LA guidelines incase of the experimental data having the maximum standard
* SD= Standard Deviation
Isotactic PP with a melt-flow index of 11 (230.degree. C./2.16 kg) and density of 0.9 g per ccm were compounded with EOC with a density of 0.86 g per ccm, melt-flow index of 1 (19O.degree. C./2.16 kg) and octene content of 25 wt%, nanosized fillers and comptibiliser at different weight ratios of PP: EOC: nanosized fillers: compatibiliser at 67: 30: 1: 2, 65: 30: 3: 2, 63: 30: 5: 2, 61: 30: 7: 2
Table II Mechanical Properties of the nanocomposite blends of the invention
Nanofiller type Nanofiller Wt% Tensile Strength (MPa) S.D Tensile Modulus (MPa) S.D. Flexural Strength (MPa) S.D Flexural Modulus (MPa) S.D. Impact Strength (J/m) S.D.
1 15.41 0.56 390.25 1.01 49.82 0.94 607.85 ±1.24 1.13 591.23 1.18
OMMT-I 3 16.82 0.91 451.16 1.03 52.45 0.81 632.11 0.97 600.21 0.79
5 17.85 0.96 474.21 ±1.33 1.05 57.56 1.01 670.44 1.04 635.11 103
7 15.11±1.01 1.09 461.11 0.98 53.14±1.01 107 603.55 1.01 607.12± 1.01 1.13
1 13.02 0 71 316.22 1.01 43.11 0.78 530.25 0.68 580.25 0.78
3 14.16 0.83 385.56 0.96 45.43 0.71 581.76 0.77 595.16 0.81
Cloisite 20A 5 15.82 0.86 416.41 1.02 52.11t1.13 1.11 612.16 1.02 620.11 1.01
7 14.01+1.27 0.91 400.01 ±1.31 1.14 49.85 1.03 590.25+1.11 1.09 601.21± 1.21 1.03
1 11.68 0.85 291.65 0.95 38.25 1.08 491.26± 1.61 1.21 569.15 0.98
Cloisite 30B 3 12 95 0.98 315.44 0.98 41.35 0.75 501.33 0.71 578 24± 1.29 1.71
5 14.26 1.02 380.21 0.78 48.06 1.04 563.15 1.02 595.62 1.01
7 13.15± 1.03 1.01 312.65±1.21 1.08 46.21± 1.2 1.13 489.41 1.03 580.21 1.13
1 10.78 0.83 212.11±1 12 1.05 31.16 0.90 470.41 0.98 556.16 ±1.13 1.18
OMMT-lt 3 11.54 0.78 280.65 1.03 37.56 ±1.28 1.31 478.56 0.87 565.23 0.91
5 1341 0.98 346.21 1.01 42.27 101 502.11± 1.01 1.11 581.24 1.02
7 12.17±1 14 1.04 299.11 0.94 39.16 1.04 485.23 1.03 569.12 1.06
1 10.22 0.87 199.65 0.98 28.45 0.88 385.12 ±1.22 1.18 539.12 0.98
Na-MMT 3 11.95 0.98 280.66 0.71 31.30 0.98 402.16 1.01 548.21 0.79
5 12.01 0.97 310.12 1.01 37.46 ±1.26 1.07 480.54 1.03 560.20±1.10 1.04
7 11.78±1.13 0.99 290.11± 1.14 1.03 30.45 1.02 395.12 1.05 550.21 1.03
A particular benefit anticipated from these nanocomposites is the generation of a blend system with significantly improved impact strength of PP while retaining the tensile strength its modulus and flexural strength its modulus. When a stress or deformation is applied to the nancomposite, the exfoliated clay layers would be anticipated to increase modulus and tensile strength.
Referring to FIG.1 and Table I, the effect of EOC content on notched izod impact strength of various PP/EOC blends at room temperature shows two transition regions. At low EOC content of less than 15 wt% a marginal increase in the impact strength was observed. Experimental findings revealed, brittle characteristics of the virgin matrix with an impact strength of about 114 J/m. Incorporation of elastomeric phase leads to an increase in the impact strength of the matrix polymer. The blend prepared incorporating 30% EOC showed optimum performance with an increase of about 380% in impact strength as compared with virgin PP due to the presence of
smaller elastomeric domains, which are effectively dispersed within the PP matrix. However, beyond 30% EOC content a decline in the impact strength of the blends was observed. This behaviour is probably due to high EOC content which results in poor dispersion within the PP matrix whereas at low EOC content it was possible to obtain blends with smaller rubber particles well dispersed in the continuous matrix. Furthermore higher EOC content probably leads to phase separation which contributes to a decrease in the impact strength.
Referring to FIG. 2 and Table I, it is evident from the test results that with the increase in EOC content, there is a decrease in tensile strength and its modulus as compared with virgin PP. This decrease wrt PP virgin were found to be 57% and 79% respectively, which is primarily due to the presence of soft elastomeric phase, that reduces the crystallinity and stress level of the virgin PP to produce shear yielding.
Referring to FIG. 3 and Table I, there is also a sequential decrease in flexural strength and flexural modulus to the tune of 312.9% and 186% respectively with the incorporation of 30 wt% EOC into PP matrix. This behaviour is probably due to the formation of pores by the elastomer phase at the interface region. The presence of elastomer in the blends linearly reduces the stiffness of the virgin polymer due to an associated reduction in the effective cross sectional area of the sample.
Mechanical properties of these nanocomposites are very encouraging and surprising. The impact strength increases more than 5 fold to 635 J/m with just 5% loading of OMMT-I (FIG. 4). Incorporation of Cloisite 20A, Cloisite 30B and OMMT-II also increases the strength modestly to 620.11 J/m, 595.62 and 581.24 J/m at 5 wt% loading. Tensile strength of the blend also increased with addition of nanofiller, and was almost comparable to the PP matrix (FIG. 5 a, b). At this level the tensile strength of the blend was improved by a factor of 9.57% to a value of 17.85 MPa. Tensile Modulus of PP also reached to a same value, from 509 to 474.21 MPa, a much more modest reduction than expected with the incorporation of only EOC in the PP matrix. Even similar behaviour was also noticed incase of the flexural properties (FIG. 6 a, b). Flexural strength and modulus of the blend matrix increased to the tune of 291.5% and 138% respectively.
The nanocomposites prepared using quaternary ammonium intercalants exhibited better
dispersion of the clay layers within the polymer matrix than the amine intercalated (O-MMT-II) and
Na-MMT (as confirmed by increased d-spacing from WAXD). This well dispersed intercalated morphology is attributed to the modification of clay with quaternary ammonium salt which lowers electrostatic interaction between the clay layers, enlarged their intergallery spacing thus facilitating efficient dispersion of the clay. It is also clear from the TEM images in Figure 7 that the presence of compatibiliser (MAPP) significantly improves the dispersion of the nanoclay as the clay aggregates have been broken down into smaller stacks. PP/EOC/OMMT-I nanocomposites depicted improved nanomorphology with finely dispersed clay particles and better intercalated structure, which might be attributed to a higher modifier concentration as well as presence of two long alkyl units.
The above comparisons demonstrate that with the inclusion of the organically modified nanofillers, there is generally a greater impact on the impact strength of PP/EOC blend matrix. It was further found that quaternary ammonium intercalants results exhibits improved performance over alkyl amine surfactants. With increased in nanofiller loadings, the benefits may decrease, that is, the higher loading may diminish the organoclay's impact on the mechanical performance of the blends.
Referring to FIG. 7a, TEM micrograph of PP/EOC blend nanocomposite with OMMT-I nanoclay, it is observed that incorporation of OMMT-I results in exfoliated nanomorphology with improved dispersion characteristics. TEM micrograph of Cloisite 20A blend nanocomposite, FIG. 7b depicts a mixed nanomorphology with stack of intercalated clay layers. There were also evidences of few exfoliated layers within the matrix. Conversely, TEM micrographs of Cloisite 30B and OMMT-II FIG. 7c, d, showed intercalated clay layers. This well dispersed intercalated morphology is attributed to the modification of clay with quaternary ammonium salt which lowers electrostatic interaction between the clay layers, enlarged their intergallery spacing thus facilitating efficient dispersion of the clay. It is also clear from the TEM images that the presence of compatibiliser significantly improves the dispersion of the nanoclay as the clay aggregates have been broken down into smaller stacks. However, in case of OMMT-II nanocomposites, the dispersion of the clay particles was poor and many large aggregates (in microns) were observed. There are some finely exfoliated clay layers and some unexfoliated individual clay particles. This confirms less compatibility between the hydrophobic matrix polymer and OMMT-II clay organically modified with quaternary amine intercalant.
Referring to FIG. 8a, the WAXD patterns of Na-MMT shows a diffraction peak at 29 = 8.025° corresponding to a d-spacing of 12.8 ANG. The XRD pattern of modified clay (O-MMT-I, Cloisite 20A, Cloisite 30B and O-MMT-II) reveals a reflection peak at 29 = 2.3°, 4°, 5.61° and 5.74° with a
d-spacing of 31.5 ANG., 24.2 ANG., 18.5 ANG., 13.4 ANG. and 13.09 ANG. respectively (FIG. 8 b, c, d, e,). This resultant increase in the basal spacing confirms intercalation in Na-MMT clay on modification with quarternary alkyl ammonium salt and amine as surfactant. OMMT-I nanoclay exhibits a maximum basal spacing with a minimum incase of OMMT-II nanoclay. This behavior is probably due to the difference in structure of the intercalants used in the modification of Na-MMT. OMMT-II is a quarternary ammonium salt containing two long alkyl units along with a methyl and a benzyl unit on the nitrogen atom whereas alkyl amine modified OMMT-II nanoclay contains one octadecylamine as a side substituent. Increase in the alkyl chain length of the organic surfactant results in random packing arrangement within the clay layers.
Referring to FIG. 8f, 8g, 8h, 8i X-ray diffraction patterns of blend nanocomposites prepared using OMMT-I, Cloisite 20A, Cloisite 30B and OMMT-II nanoclay at 5wt% clay loading, there is an increase in the basal spacing of the nanocomposites, confirming intercalation of nanolayered clay. XRD patterns of PP/EOC/Cloisite20A, PP/EOC/Cloisite 30B and PP/EOC/OMMT-I and PP/OMMT-II exhibited intercalation corresponding to 20 = 3.15°, 4.45° and 5.54° with d-spacing of 28 ANG., 19.8 ANG., 15.9 ANG. respectively. OMMT-I nanocomposites did not exhibit any peak within the experimental range, which indicated exfoliated structure. It also demonstrated superior composite performance as evident from improved mechanical & thermal properties. Addition of compatibiliser to the tune of 2 wt% further facilitated expansion of gallery space of the nanolayers by the inclusion of polar maleic anhydride (MA) groups, which intercalates between the silicate layers. Hydrogen bonding between the oxygen group of the silicate tetrahedra and the MA groups enhanced the interiayer distance of the stacked nanolayers thereby resulting in efficient dispersion of the nanoparticles within the PP/EOC blend matrix.
EXAMPLE 15 Heat of Fusion
Thermodynamic heat of fusion data were determined by differential scanning calorimetry (DSC), the procedure for which is as follows. 6 to 10 mg of a sheet of the polymer pressed at approximately 200.degree. C. to 23O.degree. C. is removed with a punch die. This sample is annealed at room temperature for 80 to 100 hours. At the end of the annealing period, the sample is placed in a differential scanning calorimeter (Perkin Elmer 7 Series Thermal Analysis System) and cooled to -50.degree. C. to -70.degree. C. The sample is then heated at a rate of 20.degree. C./min to a final temperature of 200.degree. C. to 220.degree. C. The thermal output is recorded as the area under the melting peak curve of the sample, which is typically peaked at 30.degree. C. to 175.degree. C, and occurs between the temperatures of O.degree. C. and 200.degree. C.
The thermal output in joules is a measure of the heat of fusion. The melting point is recorded as the temperature of the greatest heat absorption within the range of melting of the sample.
Melting Temperature (Tm) and Crystallization Temperature (Tc)
T melt and T crystallization are peak temperatures from Differential Scanning Calorimetry (DSC),
run at 10.degree. C./min, heating and cooling rates.
Percent Crystallinity (Enthalpy)
Percent Crystallinity (enthalpy) was derived from the enthalpy of fusion from DSC measurements.
207 J/g is taken from the literature as the enthalpy of fusion of fully crystalline isotactic
polypropylene (B. Wunderlich, Macromolecular Physics, Vol. 3, Academic Press, 1980). Melting
Temperature (Tm) and Crystallisation Temperature (Tc)
Differential Scanning Calorimetry
Crystallization temperature (T.sub.c) and melting temperature (T.sub.m) are measured using Differential Scanning Calorimetry (DSC). This analysis is conducted using either a TA Instruments MDSC 2920 or a Perkin Elmer DSC7. Typically, 6 to 10 mg of molded polymer or plasticized polymer is sealed in an aluminum pan and loaded into the instrument at room temperature. Melting data (first heat) are acquired by heating the sample to at least 3O.degree. C. above its melting temperature at a heating rate of 10.degree. C./min. This provides information on the melting behavior under as-molded conditions, which can be influenced by thermal history as well as any molded-in orientation or stresses. The sample is then held for 10 minutes at this temperature to destroy its thermal history. Crystallization data is acquired by cooling the sample from the melt to 25.degree. C. at a cooling rate of 10.degree. C./min. The sample is then held at 25.degree. C. for 10 minutes, and finally heated at 10.degree. C./min to acquire additional melting data (second heat). This provides information about the melting behavior after a controlled thermal history and free from potential molded-in orientation and stress effects. The endothermic melting transition (first and second heat) and exothermic crystallization transition are analyzed for onset of transition and peak temperature. The melting temperatures to be reported are the peak melting temperatures from the second heat unless otherwise indicated. For polymers displaying multiple peaks, the higher melting peak temperature is reported.
Areas under the curve are used to determine the heat of fusion (.DELTA.H.sub.f) which can be used to calculate the degree of crystallinity. A value of 207 J/g is used as the equilibrium heat of fusion for 100% crystalline polypropylene (obtained from B. Wunderlich, "Thermal Analysis", Academic Press, Page 418, 1990). The percent crystallinity is calculated using the formula, [area under the curve (J/g)/207 (J/g)]*100.
Thermogravimetric Analysis (TGA)
The thermal stability was studied from TGA / DTG curves employing Perkin Elmer Pyris - 7 TGA
equipment. Samples of Degree C per minute in nitrogen atmosphere and corresponding weight loss was recorded.
Melting and crystallization behavior of virgin PP, PP/EOC blend and their nanocomposites is shown in FIG. 9 and 10. PP matrix displayed a sharp endothermic melting peak at 162.79. Degree C. The blend of PP-EOC (optimized) shows a improvement in melting point to 164.15. Degree C. The crystalinity reduces to 9.92 % for the blend from 18.43% for PP. This is because the disturbance of crystallization site due the presence of elastomeric phase in the blend. The addition of nanoclays in the blend causes the increase of melting temperature and degree of crystallinity. Due to better exfoliation of clays and further acting as heterogeneous nucleating sites nanocomposites prepared from OMMT-I shows highest melting point and degree of crystalinity in comparison to nanocomposites prepared from other clays. The crystallization temperature increased in case of the nanocomposites as compared to the PP and its blend with EOC, which is attributed to heterogeneous nucleating effect of nanoclays. The nanocomposites prepared from Cloisite 20A, Cloisite 30B and OMMT II also shows modest thermal results with an optimized result in OMMT-I which is mainly due to its greater affinity to the polymer and the exfoliation of the clay. The DSC results are tabulated in Table III.
Table III DSC results of the PP virgin, PP/EOC blend and nanocomposite blends of the invention
Composition Melting Temperature (Tm/ °C) A Hm (J/g) Xc (%) Crystallization Temperature (Tc/ °C)
PP Virgin 162 79 38.166 18.43 113.30
PP/EOC 164.15 19.237 9.29 120.42
PP/EOC/Na -MMT 164.82 18.725 9.04 121.13
PP/EOC/OMMT-I 167.17 23.367 11.28 123.61
PP/EOC/Cloisite 20A 165.67 22.128 10.68 122.54
PP/EOC/Cloisite 30B 165.79 22.592 10.91 122.06
PP/EOC/OMMT-II 165.01 20.884 10.08 121.92
* Xc calculated with taking AHm =207.00 J/g for pure PP as reference
FIG. 11 represents the TGA thermogram of blend and the nanocomposites at various clay (Na-MMT, Cloisite 20A, Cloisite 30B) loading in the temperature range of 50-600.Degree C. It is seen from the figure that with the incorporation of clay loading, there is an increase in the thermal stability of PP and blend matrix. It is also observed that the thermal stability of blend nanocomposites at 5 Wt.% OMMT-I loading is more in comparison to 5 Wt.% Cloisite 20A, 30B and OMMT-II loading. This result may be due to the better exfoliation of OMMT-I than other commercially modified as well as laboratory modified clays. Further the onset degradation temperature and percent of weight loss along with the amount of residue depicted in Table IV. This behavior was caused by the intercalation of polymer matrices between the clay galleries, which provide the resistance to thermal degradation. The rate of degradation also slowed down which might be due to better adhesion of the polymer chains to the clay surface. The slower rate of degradation and the high final loss temperature indicated the thermal insulation effect that occurs because of the shielding of the intercalated polymer chains by the clay layers. The onset temperature of degradation nanocomposites with OMMT-I shows highest stability due to the larger amount of intercalation of polymer chains in the clays. Another reason for higher thermal stability this clay nanocomposites might be due to higher thermal stability of the organic modifier, which is about 363°C. Further, the wt% of residue in the blend nanocomposites also increased as compared with the blend matrix which indicates better flammability characteristics in these materials.
The TGA results are tabulated in Table IV
Table IV TGA results of the PP virgin, PP/EOC blend and nanocomposite blends of the
Composition Onset (°C) Endpoint (°O 10% wt. Loss at (°C) 30% wt. Loss at (°C) 50% wt. Loss at (°C) 90% wt. Loss at (°C) Residue in wt. %
PP Virgin 375.03 488.89 424 456 470 492 0.0896
PP/EOC 363.86 487.28 407 448 465 488 0.2351
PP/EOC/Na-MMT 391.77 490.98 435 465 477 486 3.0135
PP/EOC/OMMT-I 439.44 489.45 461 487 494 508 2.1484
PP/EOC/Cloisite 20A 432.05 486.52 457 473 479 492 3.3520
PP/EOC/Cloisite 30B 430.05 479.26 452 467 474 487 2.1411
PP/EOC/OMMT-I 1 401.10 492.92 439 468 480 499 4.9739
We have examined PP/EOC blend nanocomposites by TEM, and have found that filler particles do not initiate failure, as expected in nanocomposites containing untreated nanofiller particles. Instead nanofiller particles were distributed throughout and were observed even in highly strained craze deformation zones. The particles there act as reinforcements. Similar deformation characteristics were observed in nanocomposites containing silica.
The nanocomposites are useful as molding resins to form mojded components for automobile applications. They can replace polyolefins such as polyethylene or polypropylene and expensive materials like ABS when improved impact resistance, decreased crack growth rates, higher thermal stability are desired.
While in accordance with the patent statutes the best mode and preferred embodiment has been set forth, the scope of the invention is not limited thereto, but rather by the scope of the attached claims.
1. A nanocomposite blend, comprising organically modified nanofiller, and at least one
thermoplastic polypropylene, metallocene catalysed polyethylene/polyethylene
elastomer; ethylene octane copolymer.
2. The nanocomposite blend of claim 1, wherein said nanofiller is selected from one or more
of montmorillonite, sodium montmorillonite, calcium montmoriflonite, magnesium
montmorillonite, laponite, hectorite, saponite, sauconite, or magadite.
3. The nanocomposite blend of claim 2, wherein said nanosized filler is organically modified
with ammonium, quaternary alkylammonium, alkyl amine derivatives of aliphatic,
aromatic or arylaliphatic amines, phosphines or sulfides or sulfonium derivatives of
aliphatic, aromatic or arylaliphatic amines, phosphines or sulfides.
4. A process of treatment the organically modified nanofiller as claimed in claims 2 and 3
wherein the clay layers are largely intercalated that influences the surface tension of the
nanofiller so that polarity and the overall surface energy value drops.
5. The nanocomposite blend of claim 4, wherein said organically modified nanofiller is
present in said nanocomposite from 1 -7 wt % of said nanocomposite.
6. The nanocomposite blend of claim 1, wherein the said nanocomposite blend comprises
of metallocene catalysed polyethylene/polyethylene elastomer (Ethylene Octene
Copolymer, EOC) to the tune of 30 to 40 wt% of total 100 wt% of Polypropylene matrix.
7. The nanocomposite blend of claim 6, wherein said nanocomposite further comprises at
least maleated thermoplastic polyolefin compatibiliser of 2-3 wt% of total 100 wt% of
8. The method according to claim 7 wherein the components are compounded in one step.
9. The nanocomposite blend of claim 8, wherein the impact strength of a molded sample of
said nanocomposite blend is at least 455% and 16.1% higher than PP matrix and the
PP/EOC blend respectively.
10. The nanocomposite blend of claim 8, wherein the tensile strength and modulus of a
molded sample of said nanocomposite blend is at least 115.6% and 343 % higher than
the PP/EOC blend.
11. The nanocomposite blend of claim 8, wherein the flexural strength and modulus of a
molded sample of said nanocomposite blend is at least 291.5% and 138% higher than
the PP/EOC blend.
12. The nanocomposite blend of claim 8, wherein the clay galleries of the nanofiller
undergoes complete exfoliation within the blend matrix when organically modified with
methyl benzyl di-hydrogenated tallow ammonium chloride as surfactant
13. The nanocomposite blend of claim 8, wherein the thermal stability of a molded sample of
said nanocomposite blend, as derived from onset temperature from TGA is at least 17.1
and 21 % higher than the PP matrix and the blend respectively.
14. The nanocomposite blend of claim 8, has substantially high impact resistance, decreased
crack growth rates, higher thermal stability, while retaining the tensile and flexural
properties of PP, can suitably replace Polyolefins viz. polyethylene or polypropylene and
expensive materials like ABS for automotive applications.
The present invention relates to melt mixing of polypropylene/ethylene octene copolymer blend and intercalated nanofiller organically modified with various quaternary alkyl amine and alkyl ammonium surfactants in presence of MAPP as a compatibilizer to form nanocomposites blend. These nanocomposites blend are found to exhibit significant improved impact strength while retaining the tensile strength and modulus and flexural strength and modulus of PP. Moreover the blend nanocomposite system can desirably improve the thermal stability of PP as well as PP/EOC.
|Indian Patent Application Number||52/KOL/2007|
|PG Journal Number||43/2009|
|Date of Filing||16-Jan-2007|
|Name of Patentee||DR. SANJAY KUMAR NAYAK|
|Applicant Address||CIPET, B/25, CNI COMPLEX, PATIA, BHUBANESWAR-751024|
|PCT International Classification Number||C08L23/00|
|PCT International Application Number||N/A|
|PCT International Filing date|