Optimization of FR Thermoplastics for Engineering Applications

Transcription

1 Optimization of FR Thermoplastics for Engineering Applications G. Reznick, Y. Bar Yaakov, J-M Lopez-Cuesta L. Utevskii and P. Georlette Dead Sea Bromine Company Ecole des Mines d'ales P. O. Box 180 6, Ave de CLAVIERES IL BEER SHEVA F ALES CEDEX ISRAEL FRANCE Abstract: The rapid development in computerized systems for the electronic and automotive industries is making them very demanding with regard to plastics properties and costs. High flow during molding, good compromise between impact and stiffness as well as tolerance to high temperature of use are some of the requirements for the plastic parts used in their production. Due to miniaturization and the consequent increase in operating temperature, more stringent flame retardancy is needed. Existing and recently introduced brominated flame retardants are essential for this type of application taking into account their nature: Most of them melt during injection molding providing a processing aid effect, specially for glass reinforced 12systems The polymeric types exhibit efficient flame retardancy providing high rates of flame retardancy with less 12bromine. New flame retardant systems for polypropylene combining brominated compounds, antimony trioxide and 12magnesium hydroxide offer optimal combination of cost and properties. Reactive processing is used to produce flame retarded polypropylene compounds with very high impact 12strength. This paper will review some applications of brominated indan, brominated epoxy oligomers and homo- or copolymers of brominated acrylate in thermoplastics for engineering applications. Introduction: Engineering plastics are polymers with high levels of properties. In addition to good mechanical properties they must have satisfactory processing characteristics and be stable during processing. Furthermore they need to be able to withstand conditions of use without losing properties or deteriorating in appearance. When these products are required to meet flame-retardancy standards this should not be at the expense of their high performance capabilities. Hence it has been necessary to develop new flame retardants which meet these special needs.

2 This paper describes the use of three types of compound offered by the Dead Sea Bromine Group which provide high levels of flame retardancy in various engineering polymers. As some applications where engineering thermoplastics are used are now being met by polypropylene, some examples of FR polyproplene have been included. POLY(PENTABROMOBENZYL)ACRYLATE Poly (pentabromonenzyl acrylate) FR-1025 is a polymeric flame retardant particularly suitable for use with polyamides and thermoplastic polyesters with or without fibre reinforcement. FR-1025 exhibits inherent advantages over other halogenated FR additives currently offered for the same applications, as a result of its polymeric nature, high bromine content and excellent thermal stability. In addition, the processability of polymers containing FR-1025 is very good. The use of FR-1025 is advantageous when the following properties are required: 22* effective flame retardancy 22* non-blooming 22* good temperature stability, long term heat - stability 22* easy processability 22* excellent compatibility with fibre reinforcement and polymer matrix 22* insoluble,hence not solvent extractable 22* chemical resistance 22* good electrical properties Being a free-flowing powder, FR-1025 is easy to compound with polymers. Moreover, it enables producers to obtain compounds with good initial colour. It is noteworthy that the softening range of FR-1025, between 190 C and 220 C, is lower than those of nylon 6, PET and PBT, leading to good mixing of the melt. This property is illustrated by similar values of the melt flow index of the compounds made from GR nylon 6 at 235 C under a load of 5 kg (see Table 1). FR-1025 also functions as a processing aid enabling lower temperatures to be used and has been shown to be easy to compound with most engineering polymers with or without reinforcement (Beneficial effects of brominated flame retardants in polymeric systems - R. Smith, L. Utevskii et al - pp Flame Retardants 96 - Inter Science Communications Ltd - January 96 - London UK). It is recommended to limit processing temperature to 290 C. Its good compatibility is used to produce low cost FR PP compound in combination with magnesium hydroxide. Table 1 shows the properties of glass-reinforced nylon 6 flame retarded with FR-1025 to UL 94 V-0 standard.

3 Table 1: Flame Retarded Glass-Reinforced Nylon 6. FR Type = None FR-1025 Composition % = = 30% GR-Nylon FR Antimony oxide PTFE* - 1 Bromine content, % Flammability = = UL 94 (1,6mm) Burning V-0 Limiting oxygen index, % Properties = = Tensile strength, MPa Elongation at break, % Tensile modulus, MPa 7,100 7,300 Izod notched impact, J/m Melt flow index, g/10 min. (235 C-5kg) *Anti-dripping agent Table 2 provides results obtained with PBT. Note that higher FR-1025 gives very high L.O.I. and contributes to improved mechanical properties.

4 Table 2: Flame Retarded and Glass-Reinforced PBT None FR-1025 Composition % = = = 30% GR-PBT FR Antimony trioxide Bromine content, % Flammability = = = UL 94 (1,6mm) Burning V-0 V-0 Limiting oxygen index, % Properties = = = Tensile strength, MPa Elongation at break, % Tensile modulus, MPa 9,021 6,469 8,041 Izod notched impact (J/m) In Tables 3 and 4 properties are reported for nylon 6,6 and PET, both reinforced and nonreinforced, flame retarded with FR-1025.

5 Table 3: Flame Retarded Nylon 6,6 Non-reinforced Glass-reinforced (30%) Composition % = = Nylon 6, FR Antimony oxide PTFE* Bromine content, % Flammability = = = = Limiting oxygen index, % UL 94, (1.6mm) NR V-0 NR V-0 Properties = = = = Yield strength, Mpa Elongation at yield, % Ultimate tensile strength, MPa Elongation at break, % Tensile modulus, Mpa Shore hardness D HDT, 1.82 MPa, C *Anti-dripping agent NR=non-rated

6 Table 4: Flame Retarded PET ================ Non-reinforced Glass-reinforced (36%) Composition % = = = = = PET FR Antimony trioxide Bromine content, % Flammability = = = = = Limiting oxygen index, % UL 94 (1.6mm) NR V-2 V-0 NR V-0 Total flaming time, sec Properties == = = = = Tensile strength, Mpa Yield strength Mpa Elongation at break, % Tensile modulus, Mpa Shore hardness D HDT, 1.82 MPa, C PENTABROMOBENZYL ACRYLATE MONOMER In addition to the polymeric FR-1025, the monomeric form, pentabromobenzyl acrylate - FR-1025M - is also available. This product has good thermal stability. It has been developed as a flame retardant additive for engineering thermoplastics. It can be copolymerized with a variety of commercial monomers or compounded via homopolymerization during reaction moulding with engineering thermoplastics. PBT, polycarbonate, nylon 6 and nylon 6,6 containing FR-1025M can meet flammability standard UL 94 V-0 while maintaining the mechanical and physical properties of the resin. FR-1025M improves the compatibility of the polymer matrix with the glass reinforcement and acts as a processing aid. It maintains the transparency of resins such as polycarbonate, crystalline polystyrene and polymethyl methacrylate. It is stable at room temperature and has excellent shelf life. Another interesting development is production via reactive extrusion of graft copolymers with EPDM enabling high impact resistance in PP homopolymer to be reached. Use of FR- 1025M in GR PBT is exemplified in Table 5

7 Table 5: Flame Retarded PBT Composition % GR PBT (30% glass) 89.5 FR-1025M 7 Antimony trioxide 3.5 Bromine content, % 5.0 Flammability = UL 94 (3.2mm) V-0 Properties = Tensile strength, MPa 109 Tensile modulus MPa 9900 Elongation at break, % 2.4 Flexural strength Mpa 172 Flexural modulus Mpa 7560 Izod notched impact, J/m 91 HDT, (1.8 MPa) C 200 CTI, volts BROMINATED TRIMETHYLPHENYL INDANE Brominated trimethylphenyl indane FR-1808 is a new environmentally friendly (DPO free) flame retardant additive based on aromatic bromine. The chemical structure (Figure 2) of this new proprietary flame retardant is compatible with most engineering thermoplastics. FR-1808 exhibits inherent advantages over other flame retardant additives currently offered for similar applications as a result of high bromine content, excellent thermal stability and melting range. Its processing aid properties enable shorter injection molding cycles and achievement of thinner wall parts. Additionally, the impact properties of polymers containing FR-1808 are usually very good. FR-1808 is an off white free flowing powder containing 73% bromine by weight. Excellent thermal stability is achieved because the bromine is "aromatic bromine". This enables it to be used with a broad range of thermoplastic materials under various processing conditions. When processed at temperatures around its melting range, it behaves as a melt blendable flame retardant. This has important beneficial effects on properties such as impact strength and flow. Examples will be illustrated in the following sections. Enhanced flow is an especially important feature since many plastics are being designed with thinner wall dimensions. The electrical and electronic market as well as computer and business machine housing markets exemplify this. A clear need has been demonstrated by the market for enhanced flow in certain materials and FR-1808 can be an important contributor.

8 FR-1808 may be formulated into a wide variety of plastic matrices under different process conditions. Table 6 illustrates compounding conditions used for a ZSK-30 twinscrew extruder. The extruder was configured into a nine barrel geometry. A variety of melt temperatures was measured. In all cases a stable process was observed and strand colour was good. Thus FR-1808 is sufficiently melt stable to handle compounding conditions used for demanding engineering resins. The effect of FR-1808 in a PC/PBT alloy is shown in Table 7. It readily incorporates in the plastic matrix and ensures a good level of property performance. Here again, addition of an impact modifier further enhances toughness. Table 8 illustrates use in nylon 6,6 where blends of FR-1808/antimony trioxide are used alone or in combination with a surface treated magnesium hydroxide (FR-20). FR-1808 provides good flow without detrimental effect on impact while its combination with magnesium hydroxide is reinforcing significantly the moduli and enables higher CTI values. In PBT itself FR can give rise to blooming under servere conditions. However, use of a combination of FR with 1 to 2 % of brominated epoxies overcomes this problem. Table 6: Extrusion Compounding Conditions for FR-1808 =============== RESIN TYPE Extruder: ZSK-30 PBT Nylon 6,6 RPM Rate (Kg/hr.) Temperature, C = = 888Zone Zone Zones Zones 5-8/Die Melt

9 Table 7: Effect of FR-1808 on PBT/PC Properties Composition, % PBT/PC FR Impact modifier (EXL-2647) Antimony trioxide Bromine content, % Flammability = = UL 94 (1.6mm) V-0 V-0 Properties = = Tensile strength, Mpa Tensile modulus Mpa Elongation at break, % Flexural modulus, Mpa Izod notched impact, J/m Table 8: Effect of Flame Retardant on Nylon 6,6 properties Flame Retardant Ref No FR FR-1808 FR-1808+FR- 20 Composition, % = = = Nylon 6, Flame retardant Antimony trioxide Magnesium hydroxide (FR-20) Anti-drip agent (PTFE) Bromine content, % Flammability = = = UL 94 (0.8 mm) NR V-0 V-0 L.O.I., % Properties = = = Tensile strength at break, MPa Tensile modulus, MPa Elongation at break, % Izod notched impact, J/m HDT (1.8 Mpa), C CTI, V

10 BROMINATED EPOXIES OLIGOMERS The Dead Sea Bromine's F-2000 series comprises a family of brominated epoxies with a broad span of molecular weights, whose chemical structure is shown in Fig. 3. F-2400 is a flame retardant high molecular weight brominated polymer recommended for use in a broad range of thermoplastics, such as PBT, PET, polyamides (nylon 6 and 66), thermoplastic polyurethanes and alloys (e.g. PC/ABS). The high molecular weight of F-2400 and its chemical structure offer the following advantages: 55- High thermal stability and thermal ageing 55- Excellent processability 55- Non-blooming 55- High UV stability 55- Non-corrosive Being a high molecular weight thermoplastic polymer, with a convenient softening range (tg = 150 C), F-2400 is a carrier of choice for various flame retardant masterbatches. Like the other grades of brominatd epoxy oligomers, F-2400 acts as binder in the polymer matrix and will contribute to less plate out and less surface migration. For instance, a PBT compound flame retarded by 11.6% of brominated Indane (FR-1808) shows a blooming of 0.9% in weight after 28 days ageing at 150 C. By adding 2% of F- 2400, this blooming is reduced by 70%. While F-2400 is exemplified in the reported results, other grades of the F-2000 series also find application. Table 9 shows the molecular weight and softening ranges of several grades. Those with lower softening points are more suitable where improved flow is required. Table 9. F-2300H F-2400E F-2400 F-2400H Mol.Wt. (x 1000) Softening Range C The usage of F-2400 in non-reinforced and glass reinforced PBT is illustrated in Tables 10 and 11.

11 Table 10: Flame Retarded PBT Composition % PBT PBT (30% GFR) Brominated epoxy oligomer (F- 2400) Antimony trioxide Armowax 440/Akzo Irganox B-712FF / Ciba Geigy Bromine content, % Flammability = = UL mm mm V-0 V-0 Properties = = V-0 V-2 Notched izod impact (J/m) HDT (1.8MPa) C Spiral flow [IN] MFI (250 C /2.16Kg) [g/10 min] Tensile strength at Yield, MPa Tensile modulus, MPa Flexural strength at yield, MPa Flexural modulus, MPa

12 Table 11: Flame Retarded Nylon 6. Composition, % Nylon Nylon 6 (30% GFR) Brominated epoxy oligomer (F- 2400) Antimony trioxide Hostaflon 1665 / Hoechst 1 1 Armowax 440 / Akzo 0.4 = Irganox B-712FF / Ciba Geigy 0.2 = Bromine % Flammability = = UL-94 (1.6m) (0.8m) V-0 V-0 V-0 V-0 LOI [%] 28.5 == Properties = = Izod notched impact (1/8in., RT) [J/m] HDT (1.8 MPa) [ C] Spiral Flow [IN] Tensile strength at yield, MPa Tensile modulus, MPa Flexural strength at yield, MPa Flexural modulus, MPa FR POLYPROPYLENE In addition to the engineering plastics already referred to, polypropylene is also now being employed in certain engineering applications. This has been made possible by the introduction of new flame retardants and technologies.

13 Use of pentabromobenzyl acrylate. Pentabromobenzyl acrylate can be used for the production of a flame retardant masterbatch concentrate containing 36% of bromine which provides good flame retardancy and very high impact properties in PP homopolymer. Such a masterbatch, produced via the reactive processing route using an EPDM carrier, is as follows: Composition, % by weight Pentabromobenzyl acrylate 51 Antimony trioxide 17 EPDM 31 Additives 1 Bromine content, % 36 These components have been compounded and pelletized on a twin screw counterrotating extruder Brabender PLE 751 using the following temperatures: C High processing temperatures must be selected to reach high copolymerization rates compatible with the residence time in the extruder which is between 2 and 5 minutes. Under these conditions all the monomer was grafted on the EPDM. Compounding and injection moulding of the masterbatch with polypropylene was carried out in the following manner: Composition of the blend in % by weight PP Homopolymer FR Masterbatch Concentrate 56 Additives 1.25 Compounding conditions on the same twin screw extruder as above are: Temperature profile, C Speed, rpm: 75 Injection molding was made on an Arburg Allrounder under the following conditions: Temperature profile: C Screw speed, rpm 300 Hold pressure, bar 30 Back pressure, bar 10 Mold temperature, C 48 Cycle time, sec 49 A comparison of the properties of this compound and a similar one obtained by non reactive compounding of the same PP with poly(pentabromobenzyl acrylate) and all the other ingredients is given in Table 12.

14 The results in Table 12 illustrate the outstanding combination of properties achievable by the special process used to produce this masterbatch concentrate. Impact strength at room temperature is 3 times greater than with a simple blend of all components and some 20 times greater than the PP homopolymer used as a reference. This is achieved without sacrificing tensile modulus. EPDM itself is not as effective in enhancing impact properties as its modified version. Further, the compound containing the masterbatch with FR-1025M has satisfactory impact properties after ageing for 1 month at 150 C whereas the EPDM/FR-1025 non reacted combination loses its impact properties. It must be emphasized here that usually in order to reach the UL 94 V-0 rating, a polypropylene formulation needs at least 25% of flame retardants while only 10 to 20 % is needed in styrenics or in engineering thermoplastics. Such a high loading of flame retardants produces brittleness and poor elongation properties. However, use of the FR- 1025M masterbatch technique with polypropylene provides good flame retardancy and surprisingly high impact properties even at low temperature without detrimental effect on other mechanical properties. Such compounds have good thermal aging properties at 150 C. In addition the flame retarded PP has enhanced paintability.

15 Table 12: PP flame retarded by pentabromobenzyl acrylate PP homo reference FR PP FR PP Masterbatch Non reactive Conpounding Composition, % = = = PP Homo MFI FR Masterbatch with FR-1025M = 56 = Poly(pentabromobenzyl acrylate) (FR- 1025) = = 28.7 Antimony trioxide = = 9.5 EPDM = = 17.5 Additives = Bromine content, % Flammability = = = UL 94 (1, 6mm) nr V-0 V-0 Limiting oxygen index, % Properties = = = Tensile Strength, MPa Elongation at break, % Tensile Modulus, Mpa Izod Notched Impact J/m: = = = 12room temp C MFI (230 C-2.16Kg), g/10 min Cost efficient blend of FRs for PP. A cost efficient system proposed by F. Montezin, J-M. Lopez et al (Flame retardant and mechanical properties of a copolymer PP/PE containing brominated compounds/antimony trioxide blends and magnesium hydroxide or talc - F. Montezin, J - M. Lopez Cuesta, A. Crespy and P. Georlette - to be published) for flame retarding polypropylene is the use of ternary blends of brominated FRs with antimony trioxide and magnesium hydroxide. An example of the use of these ternary blends based upon FR-1808, brominated trimethylphenyl indane, with antimony oxide and FR , a custom - treated special grade of magnesium hydroxide is given in Table 13. The ternary blend is cost efficient in terms of price per unit of volume. In addition magnesium hydroxide contributes significantly to smoke reduction.

16 Table 13: Flame retardance of PP using ternary blend FR type = Ref No FR Ternary System Br/AO FR- 20 Composition % = = = = PP block copo (MFI/12) FR Antimony trioxide FR Bromine Content% Flammability = == = - UL 94 (3.2mm) NR V-0 V-0 V-1 LO Smoke density(nbs): = = = = 11Dm flaming mode = 640 >924 = 11Max. rate. OD/min = = Properties = = = = Tensile strength, Mpa Elongation at yield, % Flexural modulus,mpa Impact-Charpy,KJ/m²: = = = = 11notched unnotched no break no break Recycling: The products described in this paper have very good thermal stability and ageing properties. As a result they are all eminently suitable in plastics applications where the ability to recycle the material is a requirement. Conclusions: Three types of compound have been described which provide flame-retardancy in engineering thermoplastics while retaining the performance levels required for the demanding applications where they are used. Poly(pentabromobenzyl acrylate) FR-1025 has excellent compatibility with fibre reinforcement and functions as a processing aid. Due to its polymeric nature it is also non-blooming. Its monomer FR-1025M can be copolymerised during reaction extrusion and provides the other

17 advantages offered by FR Brominated trimethylphenyl indane FR-1808 also has good processing aid properties and its superior melt flow enables shorter injection moulding cycles and production of thinner walls. It also gives good impact properties. The brominated epoxy series F-2000 is also non-blooming, has high thermal stability and is outstanding in resistance to U.V. Pentabromobenzyl acrylate is efficient in providing both flame retardancy and very good impact properties to polypropylene, if introduced as a masterbatch concentrate in EPDM using the reactive extrusion route. Combination of a brominated flame retardant/antimony trioxide system with magnesium hydroxide provides a good balance of properties at optimal cost. All products can be used in plastics which will be recycled. Aknowledgement: The authors would like to thank specially Dr. Joe Simons for his decisive contribution in the preparation of this paper. Many thanks also to the team of the Plastic Application Laboratory of the Dead Sea Bromine Group for their work and help which render this publication possible.