Novel Functionalised Ethylene Acrylate Copolymers as Polymer Modifiers

Transcription

1 Novel Functionalised Ethylene Acrylate Copolymers as Polymer Modifiers Novel Functionalised Ethylene Acrylate Copolymers as Polymer Modifiers Karlheinz Hausmann, Richard T. Chou and Coreen Y. Lee DuPont de Nemours International SA, Geneva, Switzerland and DuPont Company, Wilmington, DE Paper presented at Addcon World 2003 SUMMARY A novel reactive functionalised polymer modifier system based on ethylene acrylate copolymers produced by a tubular reactor polymerisation process is discussed. The tubular copolymers are unique due to the heterogeneous distribution of acrylate comonomer in the polymer chain making them more compatible with a variety of polymer systems. Because of this feature they can be used as modifiers and universal masterbatch carrier resins for a variety of polymer systems in a more appropriate way than their autoclave based homologues. The new reactive modifiers have excellent compatibility with both polar and non-polar polymers. The incorporation of a reactive functional group, such as maleic anhydride, is used to provide optimal morphology for polymer modification. Impact modification of polyamides using the new acrylate modifier is discussed. Besidessuperior impact properties, the functionalised ethylene acrylate modifier provides improved gloss in moulded parts and flow in polyamide blends compared to conventional reactive modifiers. Another feature of the finished compounds is their high elongation at break. Furthermore, the morphology of the new modifier in PA is discussed. Apart from the modification of polyamides, other applications such as coupling of mineral fillers to polymer matrices is conceivable. INTRODUCTION Most engineering polymers are modified with modifiers for functional performance, such as toughness, solvent stress resistance, etc. For example, engineering polymers such as polyamides (PA), polyethyleneterephthalate (PET), and polybutyleneterephthalate (PBT), are all modified to improve impact toughness for auto and appliance applications. Due to cost and performance pressures there is a continued need to develop new modifiers. Tubular -produced copolymers of ethylene and acrylate esters meet both cost effectiveness and performance requirements. Typical ethylene-acrylate copolymers have traditionally been manufactured in high-pressure autoclaves, in which the raw materials are well mixed to create a uniform product. The acrylate copolymers for this study, on the other hand, are produced in a high-pressure free radical polymerisation process using a long small-diameter tube reactor. The reactivity of the acrylate monomers is much higher than that of ethylene, which leads to a high level of incorporation of acrylate monomer at the beginning of the polymerisation and a low level of incorporation towards the end. As a result, the copolymers have a more heterogeneous molecular architecture in acrylate comonomer distribution, while maintaining a relatively narrow molecular weight distribution. This has been discussed in detail already [1,2]. The heterogeneous polymer structure imparted by the tubular, low mixing reactor process leads to higher polarity and therefore better compatibility with a wide variety of polymers than their autoclave homologues. EXPERIMENTAL Compounding was undertaken on a 30mm W&P twin screw extruder at a temperature of approximately 300 C for PA66, 280 C for both PA6 and PBT, and at about 220 C for PP. Thereafter test specimen were injection moulded and cut respectively for the mechanical tests. Polymers & Polymer Composites, Vol. 12, No. 2,

2 Karlheinz Hausmann, Richard T. Chou and Coreen Y. Lee The following materials were used to investigate the performance of selected acrylate ester copolymers for the modification of some common engineering polymers: Materials FN-EnBA: Functionalised Tubular EBA (BA, 27 wt.%) (Fusabond A EB ) EMAMAH Ethylene Methylacrylate Maleicanhydride Terpolymer EO-g-MAH (grafted Elastomer based on an ethylene octene (EO) copolymers for PA toughening) (Fusabond MN493D) T-EMA (MA, 24 wt.%): Tubular product (Elvaloy 1224 AC) RESULTS AND DISCUSSION Tubular Copolymers as Polymer Modifiers Tubular copolymers as polymer modifiers have been discussed already (2) where we also highlighted their use as carrier resins for masterbatches, due to their excellent compatibility with a variety of base polymers and their superior thermal stability. They are compatible with polyolefins and many other engineering polymers, such as PA, PBT and ABS. They are also excellent compatibilisers for blends of PC and PBT or PC and ABS. For example, Figure 1 and 2 show transmission electron micrographs of two blends of PBT and 20 wt.% EMA: one blend contains EMA from a tubular process and the other is from an autoclave process. Figure 1. TEM image of PBT/T-EMA (80/20 wt.%) T-EBA (BA, 27 wt. %): Tubular Product (Elvaloy 3427 AC) A-EMA (MA, 24 wt.%): Autoclave Product Nylon 6: Ultramid B3 (BASF) Nylon 6 (higher MW version): Ultramid B35 (BASF) Nylon 66: Zytel 101 (DuPont) PBT: Ultradur B4500 (BASF) PP: DX5 E98 PP Copolymer FN-EMA: Functionalised Tubular EMA (MA, 24 wt.%) Three types of comparisons were undertaken. Figure 2. TEM image of PBT/A-EMA (80/20 wt.%) First we compared acrylate copolymers made in a tubular reactor with acrylate copolymers made in an autoclave reactor. Secondly, those made in a tubular reactor were compared with functionalised ethylene acrylate copolymers made in a tubular reactor. Thirdly, we compared functionalised ethylene acrylate copolymers based on tubular reactor technology with conventional ethylene acrylate maleic anhydride terpolymers in applications such as PA modification. 120 Polymers & Polymer Composites, Vol. 12, No. 2, 2004

3 Novel Functionalised Ethylene Acrylate Copolymers as Polymer Modifiers Figure 3. TEM image of PA6 containing 10% TiO 2 Figure 4. NI imapct strength of PA6 containing 10% masterbatch based on 40% T-EMA and 60% TiO 2 TiO 2 masterbatch based on 40% T-EMA and 60% TiO 2. Compared with PE based masterbatch. The tubular EMA finely dispersed together with TiO 2 and increases the impact strength compared to virgin PA Both EMA samples have an MA content of 24 wt.% and similar melt flow index. The significantly better dispersion of the tubular EMA in PBT is clearly visible. One reason for the good compatibility is the heterogeneous acrylate distribution obtained from the tubular process. This increases the effectiveness of the polar groups as compared with polymers of the same composition from an autoclave. Figures 3 and 4 are examples of a polymer-polymerfiller blend (PA6, T-EMA, TiO 2 ), which shows the suitability of the tubular EMA resin as a dispersing agent for fillers in other polymers in the form of a masterbatch. Addition of titanium dioxide, TiO 2 (6%) in the form of a masterbatch in T-EMA increases the impact strength of a PA compared with unmodified PA6. Figure 5. Impact properties modified with tubular reactor made ethylene copolymers Polymers & Polymer Composites, Vol. 12, No. 2,

4 Karlheinz Hausmann, Richard T. Chou and Coreen Y. Lee Overall, tubular acrylate copolymers provide only low performance for toughening engineering polymers. Figure 5 shows the effect of impact modification with T- EBA copolymer on different engineering polymers. It is interesting to note that the excellent impact resistance of modified PC+PBT blends may be attributed to EMA (Ethylene Methylacrylate Copolymer) acting as both a compatibilizer and an impact modifier. Because of the absence of a reactive functionality, the modified polymers have a low melt viscosity. However, comparatively poor interfacial adhesion is achieved, which is the reason for the limited increase in impact strength. Functionalised Tubular Copolymers as Polymer Modifiers It was Epstein (3) in 1979, who discovered the concept of functionalised modifiers that could achieve superior toughness at low temperatures. Polymers suitable for this task are mainly grafted polyolefins, where the graft monomer is maleic anhydride or a similar reactive moiety. During blending, an interfacial grafting provides covalent or ionic interaction between the modifier and the polymer, and this is assumed to be the key requirement for attaining high performance. This hypothesis also applies to modifiers based on tubular copolymers. For example, despite the fine dispersion of T-EMA in nylon 6 (Table 1), the Izod impact of the modified nylon 6 is not very impressive. It is obvious that fine dispersion of modifiers in nylon alone may not be sufficient to attain high impact resistance. For further improvement of the performance of ethylene-acrylate copolymer- based modifiers, a reactive moiety is introduced to enhance the interfacial adhesion. The reactive moiety of the acrylate copolymer enhances the interfacial adhesion of the modifier phase with the Nylon phase. The enhanced adhesion between the phases improves mechanical properties such as impact strength. Figure 7 (compare Figure 6) clearly shows the improvement in dispersion attributable to the reactive group visible in the finer dispersion, and Table 1 shows the notched Izod results which compare modifiers based on acrylate copolymers with those based on the functionalised acrylate copolymers. As expected, the functionalised modifier provides significantly better impact strength, even at lower temperatures, for all Nylon types. As is evident from Figure 8, the functionalised (FN) Ethylene Acrylate copolymers, EMA (Ethylene methylacrylate) FN-EMA and EBA (Ethylene Buthylacrylate) (FN-EBA) provide a seven-fold increase in notched impact strength at the 20 wt% modifier level. At lower modifier levels, nominally 10wt%, the impact strength increases at least threefold. As the trade-off, the flexural modulus decreases with increasing modifier level. The elongation at break shows a positive trend,increasing with modifier level. In order to further investigate this subject we have compared functionalised tubular acrylate copolymers with some commercially available acrylate MAH (Maleic Anhydride) terpolymers and MAH grafted elastomer type modifiers used to impart very high toughness values to polyamides. All three types of modifiers were added at 5-20wt% levels for better comparison. The functionalised tubular acrylate copolymer modifiers are novel modifiers in this respect, marketed for polyamide or polyester modification as either Fusabond A EB or Fusabond A EM series. Table 1. Impact property of Acrylate Copolymer and Functionalized Acrylate Copolymer Notched Izod of PA6 (Ultramide* B-3) with 20wt% Modifier C EMA FN-EMA Notched Izod of Modified PA6 (Ultramide* B-35) - J/m EMA FN-EMA Notched Izod of Modified PA6,6 (Zytel* 101) - J/m EMA FN-EMA Polymers & Polymer Composites, Vol. 12, No. 2, 2004

5 Novel Functionalised Ethylene Acrylate Copolymers as Polymer Modifiers Figure 6. TEM image of nylon 6/T-EMA 6/FN (80/20 wt.%) Figure 7. TEM image of nylon EMA (80/20 wt.%) Figure 8. Properties of modified nylon 6 They are characterised by cost effectiveness, with moderate impact strength improvement, particularly at room temperature and at 20-0 C and by a rather unimportant reduction in the fluidity of the final modified polyamide composition. This reduces the cycle time when moulding the finished product. Only the type FN-T-EBA was available at the time, under the tradename Fusabond A EB This grade will be fully commercialised in slightly improved form under the name Fusabond A EB 560D. When comparing these newly functionalised reactive modifiers with the other modifiers available, such as MAH terpolymers and MAH grafted polymers, it is immediately obvious that although they show a much lower impact strength in the finished PA product than MAH grafted rubber homologues, the impact strength seems to be more or less equivalent to that achieved with MAH terpolymers (Figure 9). In addition, the nylon modified with functionalised acrylate copolymers shows high surface gloss and significantly lower viscosity than is obtained with other available functionalised modifiers. This can be seen particularly when comparing the snake flow and viscosity behaviour of samples modified with FN-T-EBA and maleic anhydride functionalised examples (Figures 10 and 11). Polymers & Polymer Composites, Vol. 12, No. 2,

6 Karlheinz Hausmann, Richard T. Chou and Coreen Y. Lee Figure 9. Comparison of impact properties in PA6 at room temperature of different modifiers Figure 10. Fluidity and elongation of different modifiers Figure 11. Viscosity of different modifiers 124 Polymers & Polymer Composites, Vol. 12, No. 2, 2004

7 Novel Functionalised Ethylene Acrylate Copolymers as Polymer Modifiers CONCLUSIONS In contrast to other functionalised ethylene copolymers that are useful for nylon impact modification or masterbatch carrier application, tubular ethylene acrylate copolymers and MAH functionalised derivates of these polymers seem to be excellent modifiers for polyamides, providing a unique combination of reasonable impact strength and at the same time excellent fluidity. Although only results relating to polyamides were discussed here, similar favourable results can be expected in other reactive filled and W&C compositions and unfilled systems, such as polyesters. REFERENCES 1. Chou, R. T.; Keating, Y. K. and Hughes, L. J.; SPE ANTEC Tec. Papers, (2002), Hausmann, K; Chou, R.T. Lee, C.Y. and Rioux, B., Proceedings, Addcon 2002, Budapest. Rapra Technology Ltd. 3. Keating, M. Y. andmccord, E. F., Thermochim. Acta, 1994, 243, Epstein, B. N (Du Pont Company). U.S. Patent 4,174,358, Polymers & Polymer Composites, Vol. 12, No. 2,

8 Karlheinz Hausmann, Richard T. Chou and Coreen Y. Lee 126 Polymers & Polymer Composites, Vol. 12, No. 2, 2004