GB2499491A

GB2499491A - Compatibilised polymer blends

Info

Publication number: GB2499491A
Application number: GB1222468.9A
Authority: GB
Inventors: Baljinder Kaur Kandola; Dario Deli; Peter Ebdon
Original assignee: University of Bolton
Current assignee: University of Bolton
Priority date: 2011-12-14
Filing date: 2012-12-13
Publication date: 2013-08-21
Anticipated expiration: 2032-12-13
Also published as: GB201222468D0; GB2499491B; GB201121498D0

Abstract

A method of making a composition comprises blending two polymeric materials (a) and (b) as specified below: (a) at least one olefinically unsaturated resin, such as unsaturated polyester or vinyl ester; and (b) at least one of chemically modified phenolic resin or amino resin such as melamine resin or any other char forming resin, such as polyfurfuryl alcohol or furan resins. In preferred embodiments, component (a) is an unsaturated polyester based on phthalic acid and (b) is an allyl functionalized novolac (phenolic) resin.

Description

1

COMPATIBILISED POLYMER BLENDS

The present invention relates to polymer blends and particularly, but not exclusively, to fire retardant polymer blends.

5

Fibre-reinforced composites are finding increased usage in load-bearing structures in a variety of applications in marine, automotive and rail transport industries owing to their specific strength and stiffness properties. A serious problem with these glass-reinforced polymeric, in particular unsaturated 10 polyester and vinyl ester, composites which are the most prevalent in marine and other surface transport applications, is that they support combustion and in fire conditions burn, most often with heavy soot and smoke. Insulation can reduce the fire hazard, but does not eliminate it. Moreover the insulation adds weight and cost to apply. The combustible part of the composite is the organic 15 resin matrix. Most common methods of fire retarding the resin and hence, the overall composite involve the physical and chemical modification of the resin by either adding fire retardant element in the polymer backbone or using fire retardant additives in the resin. For unsaturated polyester and vinyl ester resins, usually halogenated chemicals are used. While the presence of 20 halogen significantly reduces the flammability of the resin, due to increasing environmental awareness and strict environmental legislations thereof, halogen - containing fire retardants are being strictly scrutinised. When non-halogen flame retardants are used, invariably they are required in large quantities (>30% w/w) to achieve the required level of fire retardancy. High

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concentrations of additives, however, can reduce the mechanical properties of the composite. Moreover, they also affect the resin's processability for resin transfer moulding techniques, commonly used for these types of composites. Nanoscopic additives, such as organically modified clays, have been 5 uniformly dispersed within the polymer matrix (5-10%, w/w) to reduce the peak heat release value by up to 70% for many resin systems. An alternative means of improving flame retardancy is to co-blend the matrix polymer with one having reduced flammability or even inherent flame retardancy such as a phenolic resin which also has cost advantages compared with the unsaturated 10 polyester and vinyl ester resins. Unfortunately, matrix polymers like polyesters and vinyl esters are incompatible with phenolic resins.

The present invention has been made from a consideration of this.

15 According to a first aspect of the present invention there is provided a method of making a composition comprising blending two polymeric materials (a) and (b) as specified herein:-

(a) at least one olefinically unsaturated resin such as unsaturated polyester or vinyl ester; and 20 (b) at least one of chemically modified phenolic resin, an amino resin, such as melamine resin, or any other char forming resin, such as polyfurfuryl alcohol orfuran resins.

3

According to a second aspect of the present invention there is provided a composition comprising a blend of two polymeric materials (a) and (b) as specified herein:-

(a) at least one olefinically unsaturated resin, such as an unsaturated 5 polyester or vinyl ester; and

(b) at least one of chemically modified phenolic resin, an amino resin such as melamine resin or any other char forming resin, such as polyfurfuryl alcohol orfuran resins.

10 The present invention describes the means whereby the physical and/or mechanical and/or chemical properties (especially thermal stability and flame retardance) of olefinically unsaturated polymeric resins, such as unsaturated polyester and vinyl ester resins, are improved by the homogeneous blending and co-curing (cross-linking) of such resins with appropriately chemically 15 modified, thermally stable, char-forming thermosets, such as phenolic, amino, and furfuryl resins, to give a miscible, co-cured polymer blend in the form of an interpenetrating and/or co-continuous polymer network.

In one embodiment of the invention the composition is a composite 20 composition comprising a series of fibres within the polymer matrix.

The invention may advantageously be used in the production of fire retardant compositions.

4

This invention offers a step change in the fire retardancy approach to polymeric systems, by blending the base resin with an inherently flame retardant resin. Char forming resins such as phenolic and melamine resins can be termed as nonflammable, as when subjected to flame, they char rather 5 than melt or burn. Thus, they can be used in applications where the flammability and smoke production are of concern such as the interior of aeroplanes, rocket nozzles and other aerospace applications.

The blending of different and normally incompatible polymers is not a new 10 concept for preparing new materials that combine the excellent properties of more than one polymer, to mask the weaknesses of one polymer by the strengths of the other and vice versa. However, the main problem is the incompatibility of unsaturated polyester/vinyl ester and phenolic resins owing to the different polarity (low miscibility) and curing mechanisms. 15 Incompatibility in a blend can normally cause phase separation, which is detrimental to the blend's properties compared to those of individual components. In this particular case certainly the mechanical strength could be affected, which would interfere with their use in fibre-reinforced composites for structural applications. A possible way by which compatibility might be 20 achieved is to functionalize phenolic resin with groups that can crosslink with unsaturated polymer, or at least decrease the interfacial tension between the two polymers.

5

This invention involves the compatibilising of two otherwise incompatible matrix resins in order to reduce the flammability of unsaturated polyester and vinyl ester resins. These resins are to be blended with appropriately modified phenolic, melamine and other char-forming resins such as polyfurfuryl alcohol 5 or furan resins. This involves use of compatibilisers to adjust the viscosity of the modified resin to enable the resin to be infusible for resin transfer moulding, low temperature curing, to maximize compatibility and bonding with glass fibres, and to permit up-scaling to produce large laminates structures. The composite laminates thus produced are expected to comply with the fire 10 performance requirements contained in the International Convention for the Safety of Life at Sea (SOLAS) as MMO/HSC Code (Code of Safety for High Speed craft of the International Maritime Organisation).

It is already known that resins can be blended with other resins having good 15 fire retardance. Reactive blending of two resin types may form semi interpenetrating networks (IPNs) or hybrid polymer networks (HPNs). The degree of the network interpenetration depends upon the viscosity of the two resins, dispersivity, compatibility and curing rate. IPNs developed by blending polyester and epoxy bismaleimide in vinylester oligomer and unsaturated 20 polyester; polyester- bismaleimide and epoxy have been reported in the literature; see references 1-6 below:-

1. M-S Lin, R-J Chang, T.Yang, Y-F Shih, J Appl Polym Sci, 55,1607 (1995); 72 (4), 585 (1999).

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2. H.T. Chiu, S.H. Chiu, R.E. Jeng, J.S. Chung, Polym. Degrdn. Stab. , 70, 505 (2000).

3. A.B. Cherian, L.A. Varghese, E. T. Thachil, Eur.Polym. J., 43, 1460 (2007).

5 4. Z.G. Shaker, RM Browne, HA Stretz, PE Classidy, MT Blanda, J Appl Polym Sci, 84, 2283 (2002).

5. S.J. Park, WB Park, JR Lee, Polymer J, 31 (1), 28 (1999).

6. K Dinakaran, M Alagar, J Appl Polym Sci, 85 (14), 2853 (2002);, 86 (10), 2502 (2002).

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Blends of unsaturated polyester (UP) resin with resole-type phenolic resin can show improvement in heat resistance and reductions in smoke and toxic gas evolution and heat release rates. Blending of an epoxy with an unsaturated polyester has also shown improvement in thermal stability of the latter. 15 However, as mentioned hereinbefore, unsaturated polyester and vinyl ester resins are incompatible with phenolic and other such resins due to different curing mechanisms and temperatures.

In the invention phenolic resoles and methylolmelamines are chemically 20 modified so that they can be co-cured with the vinyl ester or polyester at low temperatures. Such modification involves acrylation of a phenolic resole or melamine-formaldehyde resin with a reagent such as methacryloyl chloride, acryloyl chloride and glycidyl methacrylate to give phenolic and melamine-formaldehyde resins that can be free-radically co-polymerised with the vinyl

7

ester or polyester. The resulting resin is a unique material where the two different types of resin are entangled and cross-linked to each other and so once cured it behaves as a single matrix.

5 The main routes are:

1. Co-blend vinyl ester and polyester resins with resole and novolac phenolic, and melamine-formaldehyde resins using compatibilisers. Examples of compatibilisers include solvents such as ethanol, diethylene glycol ; surfactants such as polyvinyl alcohol, SPAN 40

10 TWEEN 85; reactive chemicals such as hydroxyethyl methacrylate.

2. Chemically modifying the phenolic and melamine-formaldehyde resins so that they can be free-radically co-cured with the vinyl ester or polyester. Modifiers include allyl chloride, methacryloyl chloride, acryloyl chloride and glycidyl methacrylate.

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In addition to the compatibility issue, unsaturated polyester and un-functionalised phenolic resins cure at different temperatures. While unsaturated polymers are cured at room temperature followed by post-curing at 80°C, the latter cures at temperatures > 190 °C. The use of acid catalysts

20 such as phosphoric acid and para-toluene sulfonic acid reduce the curing temperatures of the phenolic by catalysing its polycondensation reactions.

Specific examples of the method of the invention include any of the following:-

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1. Reactive -blending of unsaturated polyester and phenolic resin modified by acrylation or epoxide groups

2. Reactive -blending of unsaturated polyester and melamine formaldehyde resin modified by acrylation

5 3. Reactive-blending of unsaturated vinyl ester and phenolic resin modified by acrylation or epoxide groups 4. Reactive-blending of vinyl ester and melamine formaldehyde resin modified by acrylation.

10 In one embodiment of the invention one or more catalysts are used to reduce the curing temperature of modified phenolic resins.

In another embodiment of the invention one or more compatibilisers are used to increase reactivity of components of blends.

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In order that the present invention may be more readily understood specific embodiments thereof will now be described by way of example only with reference to the accompanying drawings in which:-

20 Fig. 1 shows DSC curves for uncured, cured and post cured unsaturated polyester/functionalized phenolic 70:30 mix;

Fig. 2 shows the variation of tan delta with temperature for unsaturated polymer, phenolic resin, functionalized phenolic, unsaturated

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polymer/functionalized phenolic 70:30 mix and unsaturated polymer/phenolic resin 70:30 mix;

Fig. 3 shows TGA curves of unsaturated polymer, phenolic resin and their blend (50:50 mix) with catalyst in air.

5

Examples

1.1 Materials.:

Unsaturated Polyester (UP): A phthalic anhydride-based unsaturated 10 polyester resin (Crystic-406PA, Scott Bader)

Radical Catalyst: Methyl ethyl ketone peroxide (Catalyst M, Scott Bader) Phenolic resin (Ph): A novolac resin (Durez 33156, Sumitomo Bakelite Europe NV)

Functionalized Phenolic (Ph-f): An allyl functionalized novolac resin.

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1.2. Polymer Preparation. Two types of formulations prepared for this work are given in Table 1.

The UP was prepared by mixing the resin with 2 wt % of catalyst M in a 100ml beaker. The mixture was stirred for 10 minutes and placed in a 10x10cm 20 square mould. The specimen was then cured at room temperature for 24 h and post-cured at 80°C in an oven for 4 h. Both Ph and Ph-f samples were prepared by placing the pure resin in a 10x10cm square mould and cured at room temperature for 24 h followed by post cure increasing the temperature step by step up to 200°C.

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The blends reported in Table 1 were prepared by mixing appropriate quantities of UP and the Ph resins. As a general procedure, UP and either Ph or Ph-f were mixed with a mechanical stirrer in a 100 ml beaker. The required quantity of catalyst M (2 wt % UP resin) was added into the resin mixture 5 which was stirred for another 10 minutes. The resulting resin was finally transferred to a 10x10 cm square mould, cured at room temperature for 24 h and post cured step by step up to 190°C.

Fibre-reinforced composites were prepared by impregnating 8 layers of woven-roving glass fabrics with unsaturated polyester, functionalized phenolic 10 (Ph-f) and their blends. Their mechanical properties are given in Table 2.

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1.3. Results

1.3.1. Curing and flammability behaviour of blended resins

Functionalised phenolic (Ph-f) has at least two major advantages as compared to an un-functionalized Ph. Firstly, it is a slow curing resin, which 5 suggest that the water developed during the slow polycondensation (partially responsible for the incompatibility with UP) can gradually evaporate during curing, diminishing the possible phase separation. Secondly, the allyl group can, in theory, crosslink the Ph-f with UP by a radical mechanism (although an allyl unsaturated group is not a very reactive group compared with a simple 10 vinyl group) and in general improve the compatibility by reducing the polarity of the phenolic resin.

The curing behavior of UP-Ph-f resin can be observed from DSC curves in Figure 1.

In both blends (UP-Ph-f 70:30 and UP-Ph 70:30) the phenolic and the UP 15 cured by completely independent pathways. As can be seen in Figure 1, the uncured UP-Ph-f 70:30 DSC displays first an exothermic peak in the temperature range 50-100°C, which represents the curing reaction of the UP by free radical mechanism and a second large exothermic peak at higher temperature (200-300°C) representing the curing of Ph-f by polycondensation 20 reaction. A third very small peak can also be observed around 170-180°C. Such a peak was found neither in the DSC curve of the uncured Ph-f (performed without a radical initiator) nor in that of UP. This suggests that a new reaction is occurring which most probably involves the allyl groups of the Ph-f as such a reaction is expected at much higher temperature than that in

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UP. In the cured sample it can be seen that the UP is completely cured as the exothermic peak between 50-100°C has entirely disappeared. At this stage UP is entangled with the partially cured Ph-f in which only the allyl groups are reacted as evidenced by the absence of the peak at 170-180°C. Complete 5 curing of the blend by polycondensation of the methylol groups of the Ph-f is achieved only after post curing as confirmed by the absence of any sort of peak in the DSC curve of the post cured blend.

DMA was carried out to study the compatibility of the blends. Figure 2 reports 10 the variation of tan delta with temperature in which the maximum in tan delta also represents the glass transition temperature (Tg) of the thermoset. As expected, pure resins such as UP, Ph and Ph-f display a single tan delta peak which corresponds to a single Tg. On the other hand UP-Ph 70:30 shows an intrinsic incompatibility displaying a broad Tg which is the result of the two 15 different overlaid Tg transitions: the first related to the UP and a second one to the Ph. In other terms, the two resins cure entangled with one another but retain their own properties and Tg. However, the Ph-f displays only one tan delta peak and one Tg. This indicates that owing to allyl groups present in Ph-f, the two networks can crosslink during curing and now behave as a single 20 matrix.

The flammability behavior of the resins is shown in Table 1, where it can be seen that most flammability parameters, ie. limiting oxygen index, self ignition temperature, time-to-ignition in cone calorimetric test, peak and total heat

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release rate, smoke release for blended resins are less than those for unsaturated polyester resins.

The mechanical properties of fibre-reinforced composites in Table 2 show that 5 the inclusion of functionalised phenolic in UP does not affect latter's flexural and impact properties, which is important considering that phenolic resin matrices are generally very brittle.

1.3.2. Lowering of curing temperature of phenolic resin and UP-Ph 10 blends

Using PTS catalyst, the curing temperature of Ph and UP-Ph blends could be reduced from 190 to 140°C. Thermal degradation behavior of these resins is shown in Figure 3, which indicated that the use of catalyst has no adverse effect on the properties of the resins.

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Table 1. Flammability behavior of UP, phenolic (Ph), functionalized phenolic (Ph-f) and their blended resins

Sample

Self

LOI

Cone results at 50 kW/m2

composition ignition temp (°C)

(%)

TTI (s)

PHRR

(kW/m2)

THR

(MJ/m2 )

Smoke (m2/kg)

UP

452

17.9

23

1093

44.9

1086

Ph

*

23.0

36

482

22.0

619

UP-Ph 50:50

*

19.8

36

628

26.0

790

Ph-F

506

22.2

31

713

31.9

882

UP-Ph-f 50:50

468

19.6

24

910

37.8

910

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Table 2. Physical and mechanical properties of glass fibre-reinforced composites with UP, and blends of UP with functionalized phenolic (Ph-f) resins

Samples

Mass fraction (%)

Flexural Modulus (GPa)

Impact Modulus (Gpa)

Thickness (mm)

Glass

Resin

UP

58

42

17.3

13.06

2.20

UP-Ph-f 70:30

62

38

17.3

14.8

2.19

UP-Ph-f 60:40

59

41

16.9

-

2.26

UP-Ph-f 50:50

59

41

17.0

12.8

2.41

It is to be understood that the above described embodiments are by way of illustration only. Many modifications and variations are possible.

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Claims

1. A method of making a composition comprising blending two polymeric materials (a) and (b) as specified herein:-

5 (a) at least one olefinically unsaturated resin such as unsaturated polyester or vinyl ester; and (b) at least one of chemically modified phenolic resin, an amino resin, such as melamine resin, or any other char forming resin, such as polyfurfuryl alcohol or furan resins.

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2. A method according to claim 1, wherein the method comprises chemical modification of component (b) using a compatibilser.

3. A method as claimed in claim 2, wherein the compatibilser comprises 15 any of a solvent, a surfactant, or a reactive chemical for component b.

4. A method according to claim 2, wherein the compatibilser comprises any of ethanol, diethylene glycol, polyvinyl alcohol or hydroxyethyl methacrylate.

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5. A method according to claim 1, wherein the method comprises co-curing the resin blend by the introduction of an unsaturated modifier to component (b) such that component (b) may then be co-cross-linked with component (a).

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6. A method as claimed in claim 5, wherein the modifier includes a monomer, such as a styrenic species or acrylic species.

5 7. A method as claimed in claim 5, wherein the modifier comprises any of allyl chloride, methacryloyl chloride, acryloyl chloride or glycidyl methacrylate.

8. A method as claimed in claim 5, wherein the co-cross-linking takes place in a free radical process at temperatures under 100°C.

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9. A method as claimed in claim 1, wherein the method includes use of one or more catalysts.

10. A method according to claim 1, wherein the method comprises 15 blending of unsaturated polyester and phenolic resin modified by acrylation or epoxide groups.

11. A method according to claim 1, wherein the method comprises blending unsaturated polyester and melamine formaldehyde resin modified by

20 acrylation

12. A method according to claim 1, wherein the method comprises blending vinyl ester and phenolic resin modified by acrylation or epoxide groups.

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13. A method according to claim 1, wherein the method comprises blending vinyl ester and melamine formaldehyde resin modified by acrylation.

5 14. A composition comprising a blend of two polymeric materials (a) and (b) as specified herein:-

(a) at least one olefinically unsaturated resin, such as an unsaturated polyester or vinyl ester; and

(b) at least one of chemically modified phenolic resin, an amino resin such 10 as melamine resin or any other char forming resin, such as polyfurfuryl alcohol orfuran resins.

15. A composition as claimed in claim 14, wherein the blend is a homogenous blend.

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16. A composition as claimed in claim 14 or claim 15, wherein component (b) is a thermosetting resin.

17. A composition as claimed in any of claims 14 to 16, wherein 20 component (b) is flame-retardant.

18. A composition as claimed in any of claims 14 to 17, wherein the composition additionally comprises a flame retardant additive.

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19. A composition as claimed in claim 18, wherein the flame retardant additive comprises a monomer possessing one or both of phosphorus and halogen containing groups.

5 20. A composite composition comprising a composition as claimed in any of claims 14 to 19 in combination with fibrous material.

21. A composite composition as claimed in claim 20, wherein the fibrous material comprises glass or carbon fibre.

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22. A composite composition as claimed in claim 20, wherein the fibrous material comprises at least one fibre mat.