Reactive Impact Modification of Polyamide 6 and 66 for Engine Bay Components

Polyamide 6 and 66 components located near the engine block are qualified against notched Charpy impact values at cold-start temperatures and after thermal aging. Kraton™ FG1924X is introduced as a maleic anhydride functionalised SEBS impact modifier because the pendant succinic anhydride group reacts with terminal amine groups in the polyamide matrix during melt compounding. This reaction forms a PA–SEBS graft copolymer that reduces interfacial tension and shifts the ductile-to-brittle transition to lower temperatures. Typical addition levels range from 5 wt% to 15 wt% in PA6 for automotive air intake parts, and from 10 wt% to 20 wt% in PA66 for radiator end tanks. The exact level is fixed by the target Charpy notched impact energy, because an excess of the elastomer lowers tensile modulus and heat distortion temperature. Mechanical acceptance is normally recorded according to ISO 179-1/1eA at -40 °C, ISO 527-1/-2 for tensile modulus, and ISO 75-2 method A for heat deflection temperature. Thermal aging is commonly carried out at 150 °C for 1,000 h under ISO 188. The saturated ethylene/butylene midblock also reduces oxidative embrittlement compared with unsaturated diene rubbers, a relevant factor in hot-air duct applications.

Compounding is performed on a co-rotating twin-screw extruder with an L/D ratio of 40:1 and vacuum devolatilisation. PA pellets are pre-dried to below 0.08% moisture content in a desiccant dryer, because residual water hydrolyses both the polyamide and the anhydride functionality. FG1924X is fed at the main throat with the PA, while glass fibre is added downstream through a side feeder when a reinforced compound is required. The barrel profile is run with the feed zone below 200 °C, the melting zone at 260–290 °C, and the die temperature held below 300 °C. Screw speed and throughput are balanced to maintain residence time between 45 s and 90 s. Longer residence times allow the anhydride–amine addition to proceed to completion, but may build molecular weight at the interface and raise melt pressure. Moulded parts include air intake resonators, coolant expansion tanks, and hot-air duct housings. The limiting processing constraint is moisture in the recycled PA fraction; incoming regrind must be re-dried or the notched impact strength will show batch-to-batch scatter.

For polycarbonate/poly(butylene terephthalate) blends used in thin-wall electronic enclosures, the dispersed rubber phase must retain a UL 94 V-0 classification while improving crack propagation resistance. FG1924X is dispersed at 3–8 wt% into the PC/PBT melt, where the anhydride grafts onto hydroxyl and carboxylic acid end groups of PBT. The saturated ethylene/butylene midblock does not introduce unsaturation that would otherwise accelerate thermo-oxidative yellowing at soldering temperatures. The compound is typically pre-dried at 120 °C for 4 h and compounded on a twin-screw extruder with barrel temperatures from 250 °C to 280 °C. Injection moulding is carried out with a melt temperature of 260–275 °C and a mould temperature of 60–80 °C. Flammability is evaluated per UL 94 at 1.6 mm, and glow-wire ignition performance is checked per IEC 60695-2-13. Mechanical validation includes ISO 180/1A notched Izod impact and ISO 527-1/-2 tensile property testing. Finished components include charger housings, miniature circuit-breaker bodies, and power-tool control housings.

The addition of FG1924X above 8 wt% is generally avoided in flame-retardant PC/PBT because the elastomer can reduce the formulation’s glow-wire ignition temperature and lower the heat deflection temperature under ISO 75-2 method A. The anhydride functionality is not suitable for polyoxymethylene matrices because acidic residues can catalyse depolymerisation. If storage humidity exceeds 60% RH, the pellets are pre-dried at 70 °C for 2 h before compounding to prevent surface defects. The main production risk is plate-out of low molecular weight maleic anhydride residues on the mould surface; tool maintenance intervals must therefore be established on the specific injection press and not transferred between different barrel sizes without trial confirmation.

What Role Does Maleic Anhydride Grafting Play in Coextruded EVOH–PE Tie Layers?

Coextruded barrier films for vacuum packaging and retort lamination rely on a thin tie layer between the polyolefin bulk layer and the ethylene-vinyl alcohol copolymer barrier layer. FG1924X is letdown into an LLDPE carrier phase at 10–30 wt% to generate a reactive tie resin. The succinic anhydride groups on the SEBS react with the hydroxyl groups of EVOH during the short melt-contact interval, forming ester linkages that resist delamination. Peel strength is measured under ISO 11339 at a 180° peel angle and 100 mm/min crosshead speed. For food-contact film structures, the converter must verify the complete multi-layer article under EU 10/2011 or FDA 21 CFR conditions of intended use; compliance is demonstrated on the finished laminate, not on the raw material alone. Non-food industrial lamination is frequently qualified using ASTM D903 or ISO 11339. The tie resin is produced either by pre-compounding FG1924X into LLDPE on a twin-screw extruder or by dry blending a pellet concentrate into the film extruder.

In blown-film coextrusion, the extruder barrel for the tie layer is operated at 190–230 °C. The die temperature is held below 240 °C to limit oxidative degradation of the EVOH layer. A minimum air-gap distance and a stable bubble are required to maintain contact between the molten layers before frost-line solidification. The final structures include high-barrier vacuum pouches, lidding films, and flexible packaging for oxygen-sensitive dry goods. Interlayer adhesion can fail cohesively in the LLDPE bulk layer or adhesively at the EVOH interface; if cohesive PE failure is observed, the tie-layer resin concentration is normally increased or the extruder output is reduced to extend the melt-contact time. In cast-film coextrusion, the same formulation is used, but the melt-contact interval is shorter and the adhesion values are more sensitive to die lip temperature uniformity.

Melt Rheology and Adhesion Failures in Two-Shot Overmolding

In two-shot injection moulding of soft-touch polyamide, PBT, or PC/ABS parts, FG1924X is compounded into a TPE-S formulation at 20–40 wt% to increase the polarity of the elastomer phase and promote mechanical interlocking and chemical bonding to the substrate. Adhesion is tested by VDI 2019 using a 90° peel fixture; acceptable values depend on the substrate and part design, but cohesive failure in the elastomer is usually required. The compound is pre-dried to below 0.05% moisture and moulded with a melt temperature of 190–230 °C. The substrate is heated in the cavity to a surface temperature of 50–80 °C before overmoulding. Holding pressure is set between 30 MPa and 60 MPa hydraulic pressure to prevent sink marks and to maintain contact during the brief interfacial reaction. Finished components include power tool housings, automotive interior grab handles, and medical device enclosures.

High viscosity at the overmoulding stage can cause jetting and poor bond coverage, so melt-flow verification is performed under ISO 1133-1:2022 at 230 °C/5 kg. If peel failure occurs at the interface, the root cause is generally insufficient melt temperature or residual moisture, not a lack of anhydride functionality. A second failure mode is gas entrapment at the substrate–elastomer interface, which requires vent slots near the flow front and a reduced injection speed. The functionalised SEBS phase also improves adhesion to amine-treated metal surfaces, but the metal insert must be preheated to at least 80 °C when insert overmoulding is used.

In halogen-free flame-retardant jacketing compounds for building wire and control cable, 150–180 phr of precipitated magnesium hydroxide or aluminium hydroxide creates a viscosity rise and reduces tensile elongation. FG1924X is introduced at 8–20 phr to react with the polar filler surface and disperse agglomerates. The compound is typically processed in a Buss kneader or a co-rotating twin-screw extruder with a filler side feeder and vacuum devolatilisation. Barrel temperatures are kept between 160 °C and 200 °C. The extrudate is pelletised under water and then dried before cable extrusion. Fire performance is assessed under IEC 60332-1-2 for flame spread, IEC 60754-1/2 for acid gas release, and ISO 4589-2 for limiting oxygen index. Tensile properties are measured on dumb-bell specimens according to ISO 527-3 or ASTM D638-14. For EU market cable compounds, the final formulation must comply with RoHS 2011/65/EU and REACH candidate-list restrictions applicable to the finished article.

Insufficient dispersive mixing leaves agglomerates larger than 5 µm that reduce smoothness of the extrudate and lower the insulation surface quality. The maleic anhydride groups react with basic sites on magnesium hydroxide, reducing surface energy differences and improving filler wetting. This permits higher filler loading without a complete loss of elongation at break. Finished products include low-smoke zero-halogen sheathing for control cables, building riser cables, and rail transit power cables. Production scrap from these compounds is difficult to rework above 15 wt% of the formulation because the first heat history consumes part of the anhydride functionality.

When Hot-Melt Formulations Require Shear Resistance and Polar Substrate Peel Strength

For automotive interior lamination and textile bonding, hot-melt adhesives are formulated with a styrene-block-copolymer base, a tackifying resin, and a plasticiser oil. FG1924X is added at 10–40 wt% of the polymer fraction when the bonded assembly must resist shear at elevated temperatures and still adhere to polar substrates such as leather, polyester fabric, or amine-treated metal. The adhesive is mixed in a sigma-blade mixer at 160–180 °C under nitrogen to limit oxidative chain scission. Viscosity is checked by a Brookfield viscometer at 180 °C, and peeled specimens are evaluated under ASTM D903 or ISO 11339. Elevated-temperature shear resistance is measured by ASTM D3163 or a static creep test at 80 °C with a specified dead load and bond area. Solvent-borne versions are prepared at 20–30% solids in toluene or cyclohexane/ethyl acetate mixtures; the solution viscosity is influenced by the polystyrene block content and the anhydride content.

The terminal products include interior trim lamination adhesives, fabric-backed seating laminates, and footwear assembly films. The anhydride groups can undergo ring-opening in the presence of moisture, so solvent containers must be sealed and hot-melt lines must be blanketed with dry nitrogen. Avoid combination with low molecular weight amine stabilisers in adhesive formulations, because they may preferentially react with the anhydride and reduce substrate bonding. Formulation changes should be validated by peel testing after 7 days of ageing at 50 °C and 90% RH, because moisture uptake at the adhesive interface can shift the failure mode from cohesive to mixed-mode failure.

Post-industrial reject streams from flexible packaging contain low levels of polyamide or polyester contamination dispersed in a polyolefin-rich matrix. These contaminants create weakness along domain boundaries and reduce tensile elongation. FG1924X is metered at 2–5 wt% into the recycling extruder as a solid concentrate. The anhydride groups react with the polar contaminants, while the SEBS backbone wets the surrounding polyolefin matrix. The process uses a single-screw recycling extruder or a co-rotating twin-screw extruder with a melt filtration screen changer of 80–120 mesh. Barrel temperatures depend on the dominant polyolefin fraction, but are generally held between 190 °C and 240 °C. Tensile properties are tested under ISO 527-1/-2, and notched impact properties under ISO 179-1/1eA.

Finished products include injection-moulded logistics trays, construction clips, and non-food packaging components. Published data for this specific recycled-stream configuration with FG1924X is limited; compounding trials must confirm whether the contaminant level is low enough to avoid blocking the melt filter. The functionalised SEBS does not remove the contamination, but it can reduce the loss of elongation at break compared with a non-compatibilised reference compound. Screen packs must be monitored for pressure differential, because excessive reaction with heavily contaminated streams can generate local viscosity inhomogeneity and streaking in the extrudate.