New brominated flame retardants meet requirements for technical plastics

Transcription

1 New brominated flame retardants meet requirements for technical plastics Brominated flame retardants continue to offer high performance and cost efficiency for plastic compounds meeting demanding applications. Pierre Georlette, worldwide technical manager for Dead Sea Bromine Group, outlines some recent developments that the company has introduced. Introduction Improvements in fire safety throughout the world continue to be vitally important. Already this year fires in China, France and Holland have claimed the lives of 35 people - a figure that could have been dramatically reduced if better flame retardancy of plastics had been applied. This aspect is by far the most important one that should be considered when specifying materials. However, flame retardants now mean more than just fire safety. In OEM s and consumers minds, flame retardants must also be outstanding performers during production, life cycle and even after the end of service life during recycling or incineration steps. A number of new products are now available that meet many of these requirements. This article will look at two of these products, tris(tribromophenyl) cyanurate and brominated trimethylphenyl indan. Tris(tribromophenyl) cyanurate is a melt blendable flame retardant that combines good impact properties and UV stability in styrenic copolymers and their alloys. Brominated trimethylphenyl indan has been introduced as a cost efficient flame retardant for polyamides where it exhibits significant improvement in flame retardancy, as well as a processing aid effect that allows shorter moulding cycles and thinner wall parts in glass reinforced plastics. Better impact properties are also observed. Tris(tribromophenyl) cyanurate Tris(tribromophenyl) cyanurate (FR-245) has been studied for applications in styrenic copolymers. Styrenic copolymers such as HIPS and ABS are mostly used for the housings of TV, audio and video equipment, PC monitors and other office equipment. As these polymers burn easily, they are often a real threat to users and fire prevention experts are requesting a reinforcement of Table 1: Properties of ABS flame retarded by FR-245 Type ABS Ref - no FR ABS V-2 (1.6mm) ABS V- (1.6mm) Composition (wt. %) ABS FR Antimony trioxide UV absorber Bromine content (%) 6 1 Properties Flame retardancy: UL 94, class Not rated V-2 V- MFI (22 C-1Kg), g/1min IZOD notched impact (J/m) HDT, 1.81 MPa-annealed ( C) UV stability, Delta E (Xenotest 3 h-astm D )

2 their flame retardancy. This is usually achieved by the use of brominated flameretardants with antimony trioxide as a synergist. Existing flame retardant products for these applications seldom meet all of the required properties. Decabromodiphenyl oxide (Deca) is cost efficient in HIPS but has poor UV stability and is not melt blendable during injection moulding. Tetrabromobisphenol A (TBBA) is cost efficient and melt blendable in ABS but has low thermal stability, poor impact properties and may not meet UV stability standards. Moreover, it lowers heat distortion temperature. S-81 and BT-93 are diphenyl oxide (DPO) free and are not melt blendable. They have fair to excellent UV stability, but have limitations in impact and injection moulding properties. Brominated epoxy oligomers (BEO) and their modified congeners (MBEO) are also DPO free flame retardants that combine good to excellent UV stability with good melt flow properties during injection moulding but suffer from rather poor impact properties. Tris(tribromophenyl) cyanurate (FR-245) is a joint development between the Japanese Company Dai-Ichi Kogyo Seiyaku (DKS) and Dead Sea Bromine Group, and aims to offer a balance of properties that include high melt flow during injection moulding, excellent light stability, good impact properties, and high heat distortion temperature (HDT). The chemical structure of tris(tribromophenyl) cyanurate combines a 67 wt.% aromatic bromine and a cyanurate segment to provide good flame retardant efficiency and UV/light stability. The flame retardant has a 4 wt.% nitrogen content, melting point of 23 C, specific gravity of 2.44 and molecular weight of 167. In thermogravimetric analysis (TGA-1 C under air) there is a 2% weight loss at 36 C, 5% at 385 C and 1% at 4 C. Use of FR-245 also enhances flow during injection moulding as it melts during the process. In addition to its good thermal stability, FR-245 is not related to diphenyl oxide chemistry and it is designed and developed to be environmentally friendly. MFI, g/1 min MBEO FR-245 Deca S-81 BT-93 Figure 1: Melt flow properties in FR HIPS Height, mm FR-245 Deca S-81 MBEO BT-93 Figure 2: Falling ball impact in FR HIPS (Dupont method-ball: 3g & 3.2mm diameter) BT-93 FR-245 MBEO S-81 Deca Figure 3: UV stability Xenotest 3h in FR HIPS (ASTM D ) Tables 1 reviews typical formulations and properties in ABS with classification V-2 and V- according to the UL 94 flame retardancy standard. Similar properties and effects are obtained in HIPS. Comparative testing between FR-245 and flame-retardants frequently used in

3 Table 2: Self ignition temperature of polyamide 6,6 and thermal stability of flame retardants. FR type Brominated Indan (FR-188) Brominated polystyrene Self Ignition temperature of 49 polyamide 6,6 ( C) Flame retardant thermal stability: 1% weight loss by TGA under N 2, 1 C/min LOI of 3% GFR polyamide 6,6 : Composition with 15 w % bromine styrenic copolymers is shown in Figures 2 to 7. In both HIPS and ABS, FR-245 is cost efficient and offers an excellent combination of melt flow, impact and light stability properties. FR-245 has undergone extensive toxicological and environmental testing and has been shown to pose no risk to health and the environment. The results of the analyses performed on FR-245 for the presence of polybrominated dibenzo-para-dioxins/ MFI, g/1 min TBBA MBEO FR-245 S-81 Figure 4: Melt flow properties in FR ABS IZOD, J/m FR-245 S-81 TBBA BEO Figure 5: IZOD notched impact in FR ABS dibenzofurans (PBDD/PBDF) have shown that it is in full compliance with the requirements of German Dioxin Ordinance and EPA TSCA Final Rule requirements. In other words, FR-245 poses no risk of PBDD/PBDF formation. Recycling studies with ABS scrap flame retarded with FR-245 have shown that a loading of 5% scrap in virgin compound can undergo six recycling steps without significant changes in tensile properties. FR-245 containing ABS also shows good behaviour after one week in a thermal ageing test at 8 C under 9% humidity. Figure 8 summarizes the influence of these treatments on maximum tensile strength. Existing applications of FR-245 in styrenic copolymers include copy machine parts, TV and video housings and housings for kitchen hood and similar devices (Figures 9 and 1). FR-245 exhibits other inherent advantages, which include a processing aid effect for thin injection moulding, good light stability and good impact and thermal stability. In PC/ABS alloys, it is preferred over phosphate derivatives if high heat distortion temperature is needed. Brominated trimethylphenyl indan Brominated trimethylphenyl indan (FR- 188) has been developed as a cost efficient flame retardant for applications in polyamides. Over the past 2 years, the use of injection grades of polyamide as a technical polymer has become more widespread. Major developments have taken place in the automotive industry where glass reinforced grades of polyamide often replace metal, reducing weight and cost. An important market is that of connectors where polyamide allows high tracking index (CTI) to be achieved. In addition to good thermomechanical properties and thermal stability during processing, these grades of polyamides are usually required to meet high standards of flame retardancy. Several flame retardant systems have been developed to meet the special needs of these applications.

4 Figure 11 summarizes the market of the various flame-retardants used in polyamides. Fifty eight percent are halogenated flame retardants preferred for their better thermal stability. Forty two percent are non halogenated types used when high tracking index is needed. There are a number of major flame retardants used in polyamides. Pyrocheck 68 is a brominated polystyrene (68% bromine) and has a high thermal stability but a high loading is needed because of its lower flame retardant efficiency. Due to its high softening range temperatures, polyamide compounds containing it have limited melt flow properties. Among brominated flame-retardants, it allows a high tracking index. Red Phosphorus is extensively used and cost efficient. A loading of around 7% gives class V- in glass reinforced polyamide but processing conditions are critical to avoid autoignition with production of highly toxic phosphine. Another major limiting factor of red phosphorus is that it is not possible to achieve lightcoloured materials. Red phosphorus is now also supplied as a masterbatch concentrate, 5% active. Melamine cyanurate is another halogen-free flame retardant but due Delta E to limited thermal stability its use is limited to non-reinforced polyamides. A loading of 12% is needed to reach the UL 94 V- standard. Melamine cyanurate gives rise to some plate-out and blooming. Dechlorane Plus (65% chlorine) is a well-established flame retardant for polyamide applications. It is recommended for UV stable applications but is rather expensive and has some limitation in thermal stability. Its market share has fallen recently as it is replaced by newly introduced flame-retardants. BEO FR-245 S-81 TBBA Figure 6: UV stability Xenotest 3h in FR ABS (ASTM D ) Brominated trimethylphenyl indan (FR- 188) has been introduced recently to the market as an alternative. It has a chemical structure that is compatible with styrenic homo- and copolymers and with several engineering thermoplastics, polyamides in particular. The material has a bromine content of 73 wt.% and a melting range of C. It has a specific gravity of 2.6 and a molecular weight of Thermogravimetric analysis (TGA-1 C under air) shows a weight loss of 5% at 325 C and 1% at 349 C. FR-188 has a number of inherent advantages when used in polyamide as Table 3: Properties of 3% glass reinforced polyamide 6,6 flame retarded by FR-188 FR type FR-188 Brominated polystyrene Ref. - No FR Composition, wt.% Polyamide 6,6 (%) Glass fibres (%) Flame retardant (%) Antimony trioxide (%) Bromine (%) Properties Flammability: LOI (%) UL 94 (.8 mm): Class V- V- NR Flexural properties: Strength (MPa) Modulus (MPa) 1,6 1,7 8,6 Notched Izod Impact (J/m) HDT, 1,82 kpa ( C) CTI - Tracking index (V) Spiral flow (cm)

5 Tensile strength, MPa a result of high bromine content, suitable thermal stability and melting range. FR-188, with its high bromine content, has an excellent thermal stability achieved because the bromine is aromatic and it can be processed at up to 3 C. Meanwhile, its decomposition temperature is sufficiently lower than Ref 2 cycles 6 cycles Thermal aging* * 1 week 8 C - 9% humidity Figure 7: Recycling and thermal ageing FR-245 in ABS Red P 22% Melamine cyanurate 16% Mg(OH) 4% Figure 8: FRs market for polyamides (US$72 million - % value 1999) Halogenated FRs 58% Figure 9: Front panel of a kitchen-hood in FR-245 ABS (Courtesy Kafrit MP Compounds) 2 that of the ignition of polyamide, which assists its efficiency. Its flame retardant efficiency has been compared with that of brominated polystyrene in polyamide 6,6. Thermal stability of both flame retardants and flash ignition temperature of polyamide 6,6 shown in Table 2 indicate that FR-188 will decompose at a temperature 5 C lower than brominated polystyrene and about 15 C before the self ignition temperature of polyamide 6,6. Table 2 also shows that the flame retardancy achieved with FR-188 in 3% glass reinforced polyamide 6,6, measured by the Limited Oxygen Index (LOI), is significantly better than with brominated polystyrene. When processed above its melting range, FR-188 behaves as a melt blendable flame retardant and has important beneficial effects on properties such as impact strength and flow. Enhanced flow is a particularly important feature for electronic devices made of glass-reinforced polyamide, which are often designed with thin wall dimensions. The processing aid effect of FR-188 means that power consumption during compounding is reduced. The effect of FR-188 in 3% glass fibre reinforced polyamide 6,6 is shown in Table 3. FR-188 is compared with a commercial grade of brominated polystyrene recommended for this application. The main advantages offered by FR-188 include a significant improvement in flame retardancy, with LOI values of more than 5 being easily achievable. In addition, good processing aid properties allow long spiral flow, these properties being particularly useful for the production of thin wall parts with glass-reinforced plastics. Thermomechanical properties such as tensile, flexural, impact and heat distortion temperature under load (HDT) are also maintained or improved and a fairly good tracking index is achieved. Similar compounds have been made and moulded with 3% glass reinforced polyamide 6 and their properties are summarized in Table 4. FR-188 exhibits the same kind of advantages as those listed earlier and V- on.8 mm (Standard UL 94) can be achieved with an economy of more than 7% addition rate of flame retardants. During injection moulding, some plateout may be observed with FR-188 but it is less important than with melamine cyanurate.

6 There are also cost advantages for injection moulders of polyamide parts, which arise from the high bromine content and FR efficiency, and the processing aid effect during injection moulding that reduces cycle times. Production of thin walled parts allows a reduction in weight and light-coloured materials can be achieved. Dead Sea Bromine Group estimates that total savings for moulders of glass-reinforced polyamide of around $25 per tonne can be achieved by replacing existing halogenated flame retardants with the new material. Glass reinforced polyamide formulations flame retarded by FR-188 have a cost similar to that using red phosphorus, taking into account the additional technology cost involved with the use of red phosphorus. Figure 1: External part of a water heating device in FR-245 ABS (Courtesy Kafrit MP Compounds) There is no risk in regard to brominated dioxins and dibenzofurans and it is in full compliance with the German Dioxin Ordinance. Many tests already undertaken have shown that it also satisfies the EPA requirements during incineration conditions simulating municipal waste treatment. Other toxicological and environmental testing programmes have shown that FR-188 poses no risk to health and the environment. Contact: Dead Sea Bromine Group Tel: Fax: georlettep@dsbg.com Table 4: Properties of 3% glass reinforced polyamide 6 flame retarded by FR-188 FR type FR-188 Brominated polystyrene Ref. - No FR Composition, wt.% Nylon 6 (%) Glass fibres (%) Flame retardant (%) Antimony trioxide (%) Bromine (%) 1 13 Properties Flammability: LOI (%) UL 94 (.8 mm): Max. flaming time (s) 3 1 Total flaming time (s) 1 1 Number of drips Class V- V- NR Flexural properties: Strength (MPa) Modulus (MPa) 9,3 9,3 7,8 Notched Izod Impact (J/m) HDT, 1,82 kpa ( C) CTI - Tracking index (V) Spiral flow (cm) Processing heat stability at 29 C - 5 minute residence time: Starting colour (DE) N/A Final colour (DE) N/A