WO1998013398A1

WO1998013398A1 - Reactive polymer processing

Info

Publication number: WO1998013398A1
Application number: PCT/GB1997/002615
Authority: WO
Inventors: Anthony Francis Johnson; Malcolm William Reid Brown; Sum-Wing Tsui
Original assignee: University Of Bradford
Priority date: 1996-09-28
Filing date: 1997-09-26
Publication date: 1998-04-02
Also published as: GB9620290D0; AU4561697A

Abstract

A process for making a modified polyolefin in which an isocyanate of formula (1), wherein R1, R2, R3 and R4 are independently cyclic, straight or branched chain alkyl or alkylene groups optionally containing nitrogen, oxygen, sulphur or phosphorus heteroatoms, m is an integer between 1 and 10 and n is an integer between 1 and 100; is added to a feedstock polymer in a reactor heated to a temperature at which said isocyanate reacts with the feedstock polymer, the amount of the isocyanate added to the reactor being controlled to control the properties of the modified polymer.

Description

REACTIVE POLYMER PROCESSING

This invention relates to reactive processing of polymers, particularly but not exclusively polyolefins especially polypropylene in an extruder or other reactor for example a conventional solution reactor. The invention also relates to real time control of polymer processing reactors.

It is usual to exercise steady state control over a reactor such as an extruder by maintaining constant values for such parameters as temperature, flow rate and ingredient composition.

US 4578430 discloses a process for controlled reduction of average molecular weight and alteration of molecular weight distribution of polyalphaolefins by a continuous addition of peroxide at a cyclic variable rate to the polymer in an extruder. The rate of peroxide addition is varied at a frequency with a period longer than the decomposi ion time of the peroxide but shorter than the passage time of the mixture through the extruder.

According to a first aspect of the present invention there is provided a process for making a modified polyolefin in which an isocyanate of formula 1

wherein R_x, R₂, R₃ and R, are independently cyclic, straight or branched chain alkyl or alkylene groups optionally containing nitrogen, oxygen, sulphur or phosphorus heteroatoms, m is an integer between 1 and 10 and n is an integer between 1 and 100; is added to a feedstock polymer in a reactor heated to a te perature at which said isocyanate reacts with the feedstock polymer, the amount of the isocyanate added to the reactor being controlled to control the properties of the modified polymer.

The amount of the isocyanate may be varied in a cyclic manner during the reaction. For example the isocyanate may be added in pulses during extrusion of the polymer. Alternatively the rate of addition of the isocyanate may be maintained at a continuous level selected to provide a modified polymer having one or more selected properties.

A preferred isocyanate is a , a ' -dimethyl -1, 3- isopropenyl benzyl isocyanate (also referred to as dimethyl meta- isopropenyl benzyl isocyanate or TMI) (2) .

TM

The polyolefin may be a polyalphaolefin for example polyethylene or polypropylene. Blends or copolymers of polyolefins may be employed. Other polyolefins may be selected. The invention finds particular application in formation of modified polypropylenes .

The propylene polymer of this invention may comprise a homopoly er, copolymer with ethylene or other alpha olefin having the formula H₂C=CHR wherein R is an alkyl radical comprising 1 to 10 carbon atoms. Preferred alpha olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-l- pentene, 1-heptene, 1-octene and 1-decene. Conjugated dienes may be employed. However, this invention also extends to terpolymers, and multi-component polymers incorporating non- conjugated polyenes in which at least one component has an active methine proton, such as that which stems from propylene monomer .

The reactor may comprise an extruder or batch reactor, for example a conventional tubular or continuous flow stirred reactor.

Operation of an extruder or batch reactor at a steady state does not facilitate control of such properties as the molecular weight, molecular weight distribution or copolymer distribution. The average content of the polymer can be modified at steady state by varying the input but the distribution cannot be varied during processing. The use of a controlled amount of an isocyanate in accordance with this invention facilitates control of the molecular weight distribution and/or functionality of the polymer. Control of the molecular weight distribution facilitates production of polymers having altered processability and flow characteristics .

The perturbations to the input of isocyanate are reflected in the composition of the processed polymer. Detection of these properties during processing allows control of the process using a processor or neural network. Furthermore such control is not limited to addition of an isocyanate .

According to a second aspect of the present invention polymer processing apparatus comprises a reactor, an input for polyolefin, an input for at least one grafting or chain scission reagent, means for controlling the amount of reagent added to the reactor in response to a control signal, a detector adapted to generate a detector signal dependent on a property of the polymer in the reactor and a processor adapted to generate said control signal in response to the detector signal .

A preferred grating reagent is an isocyanate of formula 1. Alternative grafting reagents may be selected.

The chain scission reagent may be a conventional peroxide initiator. Apparatus in accordance with the second aspect of this invention facilitates real time control of reactive polymer processing.

The reagents are preferably added in a pulsed or cyclically varying manner. The shape of the pulses may be selected to afford precise control of such properties as molecular weight distribution.

In preferred apparatus both an isocyanate and scission reagent are added either simultaneously or independently. Pulses of the two or more reagents may be in phase, out of phase or may be phased independently.

The amount of chain scission reagent may be controlled to afford a desired molecular weight distribution. The amount of the isocyanate may be controlled to control the functionality of the resultant polymer. An increased amount of peroxide has been found to reduce the viscosity of the polymer. An increased amount of TMI or other isocyanate has been found to increase the viscosity, binding capacity of adhesion capacity of the polymer.

Use of apparatus in accordance with this invention allows an extruder or other reactor to accommodate variations in properties of the feedstock. This avoids any need for blending of ingredients prior to processing. A one-step process is provided. Real time control of the process avoids waste and minimises the need for operator intervention.

The detector may comprise a visco eter, for example an in-line rheometer. Alternatively a spectrometer, for example a Raman or infrared spectrometer or ultrasound densitometer may be employed.

The amount of reagent added may be controlled using a variable or switchable pump.

Use of an extruder is preferred. The processed polymer may be pelletised in which case any perturbations need to be rapid in relation to the rate of collection of the pellets. However the present invention allows use of long perturbations in contrast to the disclosure of US 4578430. This affords a longer time for the polymer composition to reach homogeneity in an extruder. This is advantageous providing a polymer with similar properties to a blend without the need for a blending step .

In conventional processes supplies of polymers with different compositions may be stockpiled for future use. This may be avoided by use of apparatus in accordance with the present invention.

The perturbations are preferably cyclic having square wave, sinusoidal or ramp configurations. The amounts of two or more reagents may be varied in phase of out of phase as desired.

Reagent may be a polar aprotic solvent, for example dimethyl formamide or dimethyl sulphoxide.

The invention is further described by means of example but not in any limitative sense.

Polypropylene used was homopolymer PP grade Shell KY6100 (MFI-3, Shell Chemicals UK) . Peroxide used during the grafting was 2, 5 -bis (tert-butylperoxy) -2,5-dimethyl hexane (Trigonox 101) on a PP base (7.5% peroxide wt/wt of PP, Akzo Chemicals) . a, a ' -Dimethyl meta isopropenyl benzyl isocyanate (TMI) was sourced from a commercial supplier.

1. Extruder

Equipment

A computer monitored APV 2030 L/D=40/l (D=30mm) co- rotating twin screw extruder with 16 heating zones, fixed screw configuration, vent port (adjacent to die, attached to a vacuum pump system) , in-line rheological die, torque monitoring facility, microlink interface, data collection software, K'Tron (K-S-20) loss in weight feeder, liquid injector (APV) , Clextral injector pump (K20-2/PP-3) , nitrogen blanket over feed port, extractor hood, waterbath, pelletiser.

In-line rheological die

The die consists of a variable geometry slit [slit used in experiments = 40mm (width) x 2mm (height) ] containing two flush mounted melt pressure transducers (50mm apart) and two melt temperature sensors. Data collection

Die pressure, die temperature and torque are all collected at 1Hz through the microlink interface and displayed on a PC through the use of date collection software.

TMI grafting in extruder

PP pellets were added to the extruder at the main feed port through the use of a loss in weight feeder. PP/peroxide masterbatch was added with PP pellets via a second volumetric feeder, TMI was injected into a melt sealed zone in the extruder (12 L/D down the barrel from main feed port) . Polymer feedrate of 5kg/h was chosen to minimise material wastage, optimum screw speed and temperature setting were set by studying peroxide/PP degradation systems. The screw speed used in grafting experiments was 250rpm and the extruder temperature profile used during the grafting is that indicated in the Table 1 below (data in second row are the temperatures (^*C) of the respective extruder zones) . The screw speed and polymer throughput rate produced a mean residence time of 2.5 mins for the extruder.

Batches containing various TMI and peroxide concentrations were studied, the unreacted TMI and peroxide byproducts were removed at the vent port before entering the die. The modified PP was then hauled off through a water bath and pelletised. The sample was analysed by GPC and FT-IR spectroscopy .

2. Brabender

30 g of PP was heated melt/mixed at 175'C in a Brabender fro 5 min. A TMI/Peroxide mixture was then added to the polymer melt in 4 equal aliquots over a 2 min period. The polymer mixture was then mixed for 10 mins, the final peak torque was then recorded. The sample was recovered for spectroscopic and GPC analysis.

The effects of the grafting process were monitored by analysing TMI -grafted and ungrafted PP produced in the APV twin screw extruder and Brabender reactors, using the following methods .

- FT-IR analysis TMI calibration

The isocyanate group of TMI has been shown to be active in the IR spectrum and absorbs at approximately 2256 cm^"1. TMI calibration standards were produced by melt mixing PP, TMI (range = 0,0.5,, 1, 1.5, 2, 4, 5% wt/wt) and 0.5% of Trigonox 101 in a Brabender mixer. The sample was removed, cooled and ground (using a Fritsch Pulverisette P14) . Two polymer films (lOOμm) of each sample where then produced, FT-IR spectra were obtained and the absorbance of the isocyanate peak determined using the Beer-Lambert law.

Sample preparation & TMI graft content determination θg samples of PP, obtained from the reactive processing systems, where dissolved in hot xylene (150cm³) . The solution was cooled to ambient temperature and 150cm³ of acetone was added resulting in the formation of white precipitate. This was filtered, washed with small quantities of acetone and dried in a vacuum oven overnight to give a fine white PP powder. PP polymer films (lOOμm) were made from this powder using a Specac hot film press. FT-IR spectra of ^"the film was then obtained and the quantity of TMI was determined using the size of the isocyanate peak (2256 cm^"1) .

- High temperature GPC:

The following set up has been used in the analysis of degraded and TMI -grafted PP

Column: PLgel 2x mixed bed-B, 10 microns,_. 30cm

Solvent: 1 , 2-dichlorobenzene , with an ioxidant

Flow rate; l.Oml/min

Temperature setting: Column compartment = 140 ^*C

Sample compartment = 140 ^*C Pump compartment = 60 ^*C

Detector: Refractive index

Calibration: Polystyrene standards, mathematical procedure has been used to corrections for difference in polymer type . - 8 -

Sample preparation

50cm³ of solvent was added to lOOmg of sample and boiled gently for 20 mins. Then two -4ml aliquots of the hot solution was transferred to special glass vials. The sample vials were then placed in a heated sample compartment and after an initial delay of 30 mins the chromatography of the samples were carried out in a series .

- Melt Flow Index measurement (MFI)

Experiments were run on a Kayness 7050 MFI machine under ASTM conditions but using a temperature of 170C.

- Scanning Electron Microscopy (SEM)

A JEOL 6400 scanning electron microscope has been used to examine homogeneity of the PP-EVOH blends using a manification of 750X.

Table 1 : Temperature profile across extruder barrel

Hopper (*)Injection Port Vent Die

1 2 3 4 so 6 7 8 9 10 1 1 12 13 14 15 16

40 75 133 180 190 200 220 220 220 220 220 220 220 200 190 190

Claims

1. A process for making a modified polyolefin in which an isocyanate of formula 1

wherein R,, R₂, R₃ and R₄ are independently cyclic, straight or branched chain alkyl or alkylene groups optionally containing nitrogen, oxygen, sulphur or phosphorus heteroatoms, m is an integer between 1 and 10 and n is an integer between 1 and 100; is added to a feedstock polymer - in a reactor heated to a temperature at which said isocyanate reacts with the feedstock polymer, the amount of the isocyanate added to the reactor being controlled to control the properties of the modified polymer .

2. A process as claimed in claim 1 , wherein the amount of isocyanate is varied in a cyclic manner.

3. A process as claimed in claim 2, wherein the isocyanate is added in pulses during extrusion of the polymer.

4. A process as claimed in claim 2, wherein the rate of addition of the isocyanate is maintained as a continuous level .

5. A process as claimed in any preceding claim, wherein the isocyanate is α, α-dimethyl-1 , 3 -isopropenyl benzyl isocyanate .

6. A process as claimed in any preceding claim, wherein the polyolefin is a propylene polymer comprising a homopolymer, copolymer with ethylene or other alphaolefin having a formula H,C=CHR wherein R is an alkyl radical comprising 1 to 10 carbon atoms.

7. A process as claimed in any preceding claim, wherein the reactor comprises an extruder or batch reactor.

8. Polymer processing apparatus comprising a reactor, an input for a polyolefin, an input for at least one grafting or chain scission reagent, means for controlling the amount of reagent added to the reactor in response to a control signal, a detector adapted to generate a detector signal dependent on a property of the polymer in the reactor and a processor adapted to generate said control signal in response to the detector signal.

9. Apparatus as claimed -in claim 8, wherein the isocyanate is of formula 1.

10. Apparatus as claimed in claim 8 or 9, wherein the reagents are added in a pulsed or cyclicly varying manner.

11. Apparatus as claimed in any of claims 8 to 10, wherein the isocyanate and scission reagents are added either simultaneously or independently.

12. Apparatus as claimed in any of claims 8 to 11, wherein the amount of chain scission reagent is controlled to afford a desired molecular weight distribution.

13. Apparatus as claimed in any of claims 8 to 12, wherein the amount of isocyanate is conti oiled to control the functionality of the resultant polymer.