IES20060903A2 - A process for preparing a polyolefin masterbatch - Google Patents

Abstract

A process for preparing a polyolefin masterbatch comprising a modified nanoclay in a quantity sufficient to provide between 10 percent and 50 percent by weight, a polyolefin in a quantity sufficient to provide between 50 percent and 90 percent by weight and between 25 and 500ppm of an organic peroxide, wherein the polyolefin is grafted with maleic anhydride in the amount of less than 5 percent by weight of the polyolefin is disclosed. The invention also relates to a process for preparing a nanocomposite resin and an extruded article from the masterbatch.. The invention further relates to a masterbatch, nanocomposite resin and extruded article prepared by these processes. <Figure 1>

Description

Introduction The present invention relates to a process for preparing a polyolefin masterbatch comprising a modified nanoclay in a quantity sufficient to provide between 10% and 50% by weight, a polyolefin in a quantity sufficient to provide between 50% and 90% by weight and between 25 and 500ppm of an organic peroxide, wherein the polyolefin is grafted with maleic anhydride in the amount of less than 5% by weight of the polyolefin. The invention also relates to a process for preparing a nanocomposite resin and an extruded article from the masterbatch. The invention further relates to a masterbatch, nanocomposite resin and extruded article prepared by these processes.

It is well known that the addition of nano-sized fillers such as nanoclays to polyolefins, to provide masterbatches for use in the manufacture of polyolefin articles, extends the characteristic profile and brings new application potentials for the polyolefin. A polyolefin is a polymer of the alkene family of hydrocarbons. When nanoclay is added to a polyolefin the clay platelets separate and intercalate within the polymeric chains of the polyolefin. This leads to an increase in the mechanical strength, tensile modulus and dimensional stability at heat of the resultant polymer article.

One of the main disadvantages of using nanoclays is their high cost of purchase. It is also necessary to graft the polyolefins if adding a nanoclay as this results in better dispersability of the nanoclay within the polyolefin. This extra processing step of grafting the polyolefin however lowers the production efficiency as it requires additional cost and equipment and can also lead to an increase in transport costs.

In an effort to reduce costs it has been found that it is possible to directly graft the 0 polyolefin with certain monomers at the same time as blending the polyolefin with the nanoclay. As this obviates the need for an extra processing step, the overall processing cost is reduced. One of the drawbacks however with directly grafting the polyolefin while blending the polyolefin with nanoclay simultaneously is that the grafting monomers can react with the clay causing the clay platelets to bond together I rather than separate thus preventing intercalation.

Maleic anhydride is a well known grafting monomer. It is often used to make masterbatches with nanoclay for subsequent incorporation into nanocomposites.

Previously, maleic anhydride was grafted to a polyolefin prior to adding the polyolefin to the nanoclay. The maleic grafted polymeric chains of the polyolefin were then bonded to the amine polymeric chains on the modified nanoclay. Free maleic anhydride, i.e. maleic anhydride which has not been grafted onto a polymeric chain will be more reactive to the amine or OH groups present on the surface of the nanoclay.

It would previously have been postulated that at the high processing temperatures involved in the blending of polyolefin with nanoclays (~200°C) that the anhydride groups of the maleic anhydride would predominantly react with the OH groups at the edge of the nanoclay platelets thereby causing the clay platelets to bond together and stop the intercalation process. Alternatively, even if this reaction did force the clay platelets apart, it would be expected that the clay platelets would not be forced apart enough to allow the polymeric chains to cause intercalation. Other monomers have therefore been chosen previously for direct grafting with nanoclay.

US Patent Publication No. US 2005/0191490 discloses a nanocomposite comprising a nano-reinforcing material, a polymer matrix and an epoxy-functionalised graft polymer compatible with the polymer matrix. The epoxy-functionalised molecule can be added to the polymer matrix at the same time as the nano-reinforcing material such that the grafting process and the formation of the nanocomposite are conducted concurrently.

PCT Patent Publication No. WO 03/082966 discloses a cross-linkable and/or crosslinked nanofiller composition which comprises a cross-linkable and/or cross-linked ethylene (co)polymer and an intercalated nanofiller. An organic silane can be grafted 0 to the ethylene (co)polymer at the same time as the polymer and the nanofiller are being mixed.

These grafting molecules have been chosen as they would not be considered to be very active intercalating agents and thus there is less possibility of these grafting monomers reacting with the OH groups of the nanoclay platelets. The disadvantage however of using these grafting molecules is that they will not react as effectively with the polymer either and thus will not sufficiently graft the polymer. A further disadvantage of silane, is that it is a very expensive monomer and as the purpose of the invention is to reduce costs by successfully combining processing steps, the requirement of a very expensive monomer would not lead to any advantage.

Thus there is a need for a process for preparing a polyolefin masterbatch wherein the polyolefin can be grafted with a monomer simultaneously while being blended with a nanoclay but at a reduced cost.

Statements of Invention According to the invention there is provided a process for preparing a polyolefin masterbatch comprising a modified nanoclay in a quantity sufficient to provide between 10% and 50% by weight, a polyolefin in a quantity sufficient to provide between 50% and 90% by weight and between 25 and 500ppm of an organic peroxide, wherein the polyolefin is grafted with maleic anhydride in the amount of less than 5% by weight of the polyolefin, and the process comprises: adding the modified nanoclay, the polyolefin, the maleic anhydride and the organic peroxide at the same time to an extruder; mixing the modified nanoclay, the polyolefin, the maleic anhydride and the organic peroxide together in a first zone of an extruder at a temperature above the melting point of the polyolefin for at least 10 seconds to form a masterbatch mix; mixing the masterbatch mix in a second zone of the extruder at a temperature above the melting point of the polyolefin, at a screw speed of between 100 and 400 rpm and for a time period of at least four times the organic peroxide half life to form the masterbatch; such that the polyolefin is grafted with the maleic anhydride during formation of the masterbatch.

The advantage of this process is that it allows the use of maleic anhydride as a grafting monomer even during grafting while blending with the nanoclay. The advantage of being able to use maleic anhydride as the grafting monomer is that it can effectively graft the polyolefin while the polyolefin is being blended with the nanoclay. Additionally, as maleic anhydride is one of the cheaper monomers, costs are kept to a minimum.

Ideally, the masterbatch mix is mixed at a screw speed of 300rpm. This screw speed has been found to be particularly suitable when using maleic anhydride. Specifically, by mixing at a faster rate, it allows for the nanoclay platelets to more readily separate and the polymeric chains to bond with the maleic anhydride while at the same time intercalating the nanoclay.

Preferably, the maleic anhydride is added in the amount of less than 2% by weight of the polyolefin. The advantage of adding less maleic anhydride is that it further reduces the cost of the overall process.

Further preferably, the polyolefin is added in a quantity sufficient to provide between 60% and 70% by weight. In one embodiment of the invention the polyolefin is a homopolymer selected from the group comprising one or more of polyethylene and polypropylene. In another embodiment of the invention, the polymer is a copolymer selected from the group comprising one or more of butene-1, hexene-1 and 4 methylpentene-1 (4MP-1).

In a further embodiment of the invention, the polyolefin is recycled polyolefin. The advantage of using recycled polyolefin, is that it is a waste product and thus the invention also provides a process for converting recycled polyolefin into a useful article.

Preferably, the nanoclay is added in a quantity sufficient to provide between 24% and 40% by weight.

Ideally, the organic peroxide is selected from the group consisting of one or more of hydroperoxides such as bis(tert.alkyl peroxy alkyl) benzene, dicumyl peroxide, acetylenic diperoxy compound, t-butyl hydroperoxide, di-t-butyl peroxide, and dimethyl-2,5 bis(tert. butyl peroxyisopropyl)benzene and 2,5-dimethyl-2,5-di (tbutylperoxy) hexyne-3.

In one embodiment of the invention, a first portion of nanoclay is added to the extruder during addition of the polyolefin, maleic anhydride and organic peroxide; and a second portion of nanoclay is added to the extruder after addition of the polyolefin, maleic anhydride and organic peroxide. In this embodiment, preferably the amount of modified nanoclay added to the polyolefin during grafting of the polyolefin is in the region of between 5% and 25% by weight of the masterbatch; and the amount of modified nanoclay added to the polyolefin after addition of the maleic anhydride and the organic peroxide is in the region of between 5% and 25% by weight of the masterbatch. The advantage of this process is that it allows a substantial portion of the grafting process to be carried out in the first step as less clay is added. When the remainder of the clay is added in the second step the intercalation process can be completed.

According to the invention, there is also provided a process for preparing a nanocomposite resin, comprising: preparing the masterbatch by the process of the invention; and forming the nanocomposite resin by compounding the masterbatch in the amount of between 5% and 30% by weight of the nanocomposite resin with a polyolefin matrix resin.

According to the invention, there is further provided a process for producing an extruded article; comprising: preparing the nanocomposite resin by the process of the invention; and extruding the nanocomposite resin at a temperature of between 150°C and 230°C to form the extruded article.

The invention also relates to a masterbatch prepared by the process of the invention. The invention further relates to a nanocomposite resin prepared by the process of the invention. The invention still further relates to an extruded article produced by the process of the invention.

Detailed Description ofthe Invention The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to Fig. 1 which outlines in flow diagram form the process according to the invention.

All of the equipment used is well known equipment and accordingly does not require any further description.

Referring to Fig. 1, in step 1 polyolefin, maleic anhydride, modified nanoclay and organic peroxide are added to a twin screw extruder and are mixed together in the first zone of the extruder at a temperature above the melting point of the polyolefin for at least 10 seconds to form a masterbatch mix in step 2.

In step 3 the masterbatch mix is further mixed in the second zone of the extruder at a temperature above the melting point of the polyolefin and for a period of time which is at least four times the half-life of the peroxide to form the masterbatch in step 4.

The temperature of the first and second zones of the extruder is determined by the type of polyolefin used, however the temperature of both zones would generally exceed 100°C. It will appreciated that a single screw extruder could be used instead of the twin screw extruder, however the mixing capabilities of the twin screw extruder are considered to be more effective. It will further be appreciated that both single and twin screw extruders often have multiple heating zones. The first and second zones referred to herein may therefore encompass more than one such zone respectively.

The masterbatch can either be extruded with an amount of polyolefin matrix resin directly to form an extruded article, or alternatively can be firstly compounded with an amount of polyolefin matrix resin to form a nanocomposite resin which can be subsequently extruded. In the specification the term “extrusion” refers to the compacting of material in a die. Extrusion may be in the form of extrusion blow moulding, rotomoulding, injection moulding or compression moulding.

The type of polyolefin used to prepare the masterbatch is largely determined by the end use of the resultant masterbatch or nanocomposite resin. Polyolefins having higher values of molecular weight are generally used for blow-moulding processes where the resultant nanocomposite resins can be extruded to form blow moulded containers such as barrels, bottles or drums. The molecular weight of the polyolefins would generally be in the range of up to about 50,000 to 300,000 and more preferably between 100,000 and 200,000 daltons and the density would generally not exceed 1g/cm3.

The masterbatch polyolefin and the polyolefin matrix resin can be any suitable homopolymer such as polyethylene and polypropylene or a copolymer such as butene-1, and hexene-1, and 4 methylpentene-1 (4MP-1). Recycled polyolefins obtained from mechanical recycling of polyolefins can also be used.

The nanoclay which is added may be a natural or synthetic silicate clay. Suitable types of nanoclays are the smectite clays which include montmorillonite, saponite, beidellite, nontronite and hectorite or any analogue thereof. The nanoclay should also be modified by a cation exchange with an alkyl ammonium ion as this allows a better interaction with the polyolefins. After the nanoclay has been organically modified, the polarity and thus hydrophilicity of the nanoclay become decreased, as a result the nanoclay can be more effectively mixed with the polyolefin. The nanoclay has a large surface area for interaction with the polyolefin and comprises swellable nanoclay platelets which disperse within the polymeric chains of the polyolefin. It has been found that the nanoclay platelets both assist in increasing the formation of crystalline sites on the polymeric chains and in plating out the amorphous regions of the chains.

The amount of maleic anhydride required will depend on the reactivity of the nanoclay and the level of grafting of the polyolefin that is required. The maleic anhydride modifies the hydrophilicity of the polyolefin thus improving dispersion of the nanoclay therein. Maleic anhydride is the anhydride of cis-butdenedioic acid (maleic acid). Maleic anhydride has a cyclic structure with a ring containing four carbon atoms and one oxygen atom. When maleic anhydride is mixed with polyolefin during grafting the carbon-carbon double bond of the maleic anhydride is grafted onto the polyolefin chain and hence becomes a pendant functional group.

Surprisingly, it has been found that when nanoclay is blended with maleic anhydride and polyolefin during grafting of the polyolefin that the maleic anhydride in fact helps the polyolefin to intercalate the clay. This is caused by the anhydride group ring opening and the oxygen atom attaching itself to the clay. Either before, during or after this reaction between the maleic anhydride and the clay, the carbon - carbon double bond of the maleic anhydride can graft onto a polymeric chain in the polyolefin.

Optionally, a further amount of modified nanoclay can be added to the polyolefin after addition of the maleic anhydride and organic peroxide thereto. In this embodiment, in the region of 50% of the total amount of modified nanoclay can be added to the polyolefin in the first zone of the extruder at the same time as adding the maleic anhydride and organic peroxide. The remaining 50% of the modified nanoclay can then be added after addition of ail of the other components but also in the first zone of the extruder. In another embodiment, this remaining 50% can be added in the second zone of the extruder however in this embodiment, it should be ensured that there is sufficient length in the remaining part of the extruder so that sufficient mixing of the nanoclay with the remaining components can be achieved.

Thus the length of the specific zones of the extruder available, will determine the amount of nanoclay which can be added in each zone. It will be appreciated that even if a high amount of nanoclay is added in the second zone of the extruder that at this stage only some of the polyolefin will have been grafted by the maleic anhydride.

The organic peroxide should have a half-life in the region of between 1 and 120 minutes at a temperature of 150°C. Information on the rate of decomposition of organic peroxides at various temperatures is available from the supplier of the organic peroxide or may be determined by those skilled in the art. The decomposition rate should be as low as possible so that mixing of the nanoclay with the polyolefin during grafting of the maleic anhydride onto the polyolefin is achieved prior to substantial decomposition of the organic peroxide.

The organic peroxide can be fed into the extruder separately or can be pre-combined with an additional polyolefin and fed into the extruder in the form of a composition. Additionally, the organic peroxide can be combined with the polyolefin, prior to grafting the polyolefin and fed into the extruder in this form. As the organic peroxide acts as the catalyst in the grafting reaction it should be added to the extruder either at the same time as the maleic anhydride, or just before or after so that maximum catalysis of the grafting reaction can occur.

The amount of organic peroxide required depends on the characteristics of the polyolefin. For example a high density homopolymer having a narrow molecular weight distribution would generally require less organic peroxide than a low density copolymer having a broad molecular weight distribution. The amount of organic peroxide required can also depend on the amount and nature of any additives in the masterbatch mixture.

Example 1: Mechanical properties of test pieces.

Preparation of Masterbatch Formulations Materials: Polyolefin: Lupolen 5261Z HDPE, Fina SI 508 HDPE Exon LLDPE 6201 Maleic Anhydride (MA) Modified Nanoclay: 130P Nanoclay ex Nanocor Organic Peroxide: Benzoyl peroxide (BP).

Equipment: Prism 16mm twin screw extruder, powder feeder, pellet feeder.

The different masterbatch formulations were made up using the above materials and equipment in the amounts shown in Table 1.

Table 1 Masterbatch (MB) HDPE (%) LLDPE (%) MA (%) 130P (%) BP (ppm) MB1 (SI 508) 57.294 1.5 1.2 40 60 MB2 (SI 508) 58.794 — 1.2 40 60 MB3 (Lupolen) 57.294 1.5 1.2 40 60 The formulations was made up according to the following processes.

MB1: For MB1 the BP, MA, LLDPE and I30P were pre mixed by hand and put in a powder feeder and the HDPE (SI508) was put in a pellet feeder. Both feeders were let in at the throat of the barrel of the extruder. The screw speed of the extruder was set to 300rpm and the throughput at 3Kg/hr. Torque was noted and was maintained at 55-60%.

MB2: The process for MB2 was the same as MB1 except that no LLDPE was used and the torque remained steady at 60%.

MB3: For MB3 Lupolen was used instead of SI508 as HDPE, and as this is in powder form all materials were pre mixed and put in the powder feeder. Screw speed and throughput remained at 300rpm and 3Kg/hr and torque remained in the region of 60% Each of the masterbatch formulations comprised 40% modified nanoclay by weight of the masterbatch.

The twin screw extruder consisted of a 29 cm melting zone with a constant flight depth of 4 mm, followed by a 4.5 cm long mixing section consisting of 12 mixing blocks. The final zone was 6.5 cm, again with a constant flight depth of 4 mm.

The temperature profile for the twin screw extruder was as follows: Die Zone 3 Zone 2 Zoned Throat (°C) 200 190 140 85 55 1.5 Kg of solidified test pieces for each formulation were collected from the extruder for testing. io Preparation of Nanocomposite Resin 6g of the resultant masterbatch test pieces were let down into to 44g of Lupolen HDPE in a Brabender plastograph EC mixer at 180°C and 60 rpm. The components were added over a 2 minute period and then mixed for a further 8 minutes. They were then compression moulded on a press.

Analysis Flexural modulus was evaluated on the resultant 2 mm sheets using 60mm long, 12mm wide strips, a test span of 40mm and a test speed of 2mm/min. In all other respects the testing complied to IS0178.

The properties of the test pieces are shown in Table 1.

Table 1 Sample Flex Modulus (GPa) Improvement Vs Lupolen (%) Lupolen reference 1.05 88% Lupolen 12% MB1 1.181 12% 88% Lupolen 12% MB2 1.142 9% 88% Lupolen 12% MB3 1.391 32% Each of the nanocomposites showed a significant improvement over the polyethylene reference material.

In this specification the terms “comprise, comprises, comprised and comprising” and 5 the terms “include, includes, included and including” are all deemed totally interchangeable and should be afforded the widest possible interpretation.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail within the scope of the claims.

Claims (5)

1. A process for preparing a polyolefin masterbatch comprising a modified nanoclay in a quantity sufficient to provide between 10% and 50% by weight, a polyolefin in a quantity sufficient to provide between 50% and 90% by weight and between 25 and 500ppm of an organic peroxide, wherein the polyolefin is grafted with maleic anhydride in the amount of less than 5% by weight of the polyolefin, and the process comprises: adding the modified nanoclay, the polyolefin, the maleic anhydride and the organic peroxide at the same time to an extruder; mixing the modified nanoclay, the polyolefin, the maleic anhydride and the organic peroxide together in a first zone of an extruder at a temperature above the melting point of the polyolefin for at least 10 seconds to form a masterbatch mix; mixing the masterbatch mix in a second zone of the extruder at a temperature above the melting point of the polyolefin, at a screw speed of between 100 and 400 rpm and for a time period of at least four times the organic peroxide half life to form the masterbatch; such that the polyolefin is grafted with the maleic anhydride during formation of the masterbatch.

2. A process for preparing a masterbatch, substantially as described hereinbefore with reference to the accompanying examples and drawing.

3. A process for preparing a nanocomposite resin, comprising: preparing the masterbatch by the process as claimed in claims 1 or 2; and forming the nanocomposite resin by compounding the masterbatch in the amount of between 5% and 30% by weight of the nanocomposite resin with a polyolefin matrix resin.

4. A process for producing an extruded article; comprising: preparing the nanocomposite resin by the process as claimed in claim 3; and extruding the nanocomposite resin at a temperature of between 150°C 10 and 230°C to form the extruded article.

5. A masterbatch prepared by the process as claimed in any of claim 1 or 2.