Compounding of aluminium trihydrate and magnesium dihydroxide filled LLDPE/EVA-based halogen-free flame retardant jacketing compounds with Arkema OREVAC® C306 maleic anhydride modified linear low density polyethylene is carried out on co-rotating twin-screw extruders with L/D ratios from 40:1 to 52:1 and barrel zones set between 150°C and 210°C. The grafted LLDPE is typically metered at 2–6 wt% of the polymer phase when filler loading is in the 120–180 phr range for ATH or a blend of ATH and MDH. The anhydride groups undergo esterification with the hydroxyl-terminated surfaces of ATH and MDH during the melt residence time, lowering apparent melt viscosity and shifting the torque curve downward relative to an unmodified compound. Compounding lines processing this class of material normally require atmospheric and vacuum venting because surface moisture on ATH is released at the main feed throat; vacuum levels below -0.08 MPa are typical on the downstream vent to limit residual volatiles. If the vent is overloaded or filler is not pre-dried to 80–110°C when ambient relative humidity exceeds 60%, the strand can show internal voiding and surface roughness at pelletising. Tensile strength and elongation at break of compression-moulded sheets are evaluated according to ASTM D638-14; for typical ATH-filled LLDPE/EVA compounds, tensile strength falls in the range of 8–14 MPa and elongation at break decreases from above 200% for unfilled LLDPE to 20–50% at high filler loading. The maleated polyolefin raises elongation relative to the same formulation without coupling agent, but the improvement depends on filler particle size distribution and surface treatment. Fire performance is assessed by cone calorimetry or by IEC 60332-1-2 for single-wire flame propagation; the compound remains halogen-free under IEC 60754-1 and low smoke under IEC 61034-2 when the base resin system is selected accordingly. Processing should not exceed 230°C melt temperature because the succinic anhydride ring can decompose or undergo side reactions that reduce coupling density and produce coloured degradation products. The upper temperature limit is narrower when the compound contains maleated EVA or zinc stearate as a lubricant; zinc carboxylate interactions with the grafted anhydride can increase melt viscosity and generate gel-like defects in extruded jackets.

What limits the use of this LLDPE-g-MAH grade in 3LPE tie layers?

Three-layer polyethylene external pipe coating systems rely on an intermediate tie resin that wets the fusion-bonded epoxy primer and fuses to the HDPE topcoat. OREVAC® C306 can function as that intermediate layer when it is extruded through a flat die or side-fed onto the rotating pipe at melt temperatures of 220–250°C. Steel pipe preparation normally begins with blast-cleaning to Sa 2½ according to ISO 8501-1:2007 and an anchor profile of 50–100 µm; the FBE primer is sprayed onto the heated pipe at 180–230°C surface temperature. The grafted maleic anhydride reacts with residual epoxy and amine groups in the FBE during the brief residence time before the HDPE topcoat is applied. Coating trials and qualification are performed under DIN 30670:2019-10 or ISO 21809-1:2018 for factory-applied coatings, with tie-layer thickness of 150–300 µm and total coating thickness of 2.0–3.5 mm depending on pipe diameter. Peel adhesion at 23°C is tested after 24 h; commercial 3LPE tie systems commonly target 30–50 N/cm peel force, but published data for this exact LLDPE-g-MAH grade in full 3LPE qualification is limited, so adhesion must be verified on the actual pipe line and FBE primer. Cathodic disbondment is assessed at 65°C for 30 days using ASTM G42-11, with a radius of disbondment usually below 10 mm for qualified systems. A processing conflict arises from the LLDPE backbone: the tie layer has lower high-temperature dimensional stability than the HDPE topcoat, and under slow line speeds with radiant heat from the topcoat extruder it can sag or tear before quenching. Accumulated condensate on the FBE surface before tie application must be avoided because hydrolysed maleic anhydride becomes acidic and can interfere with epoxy cure progression. For pipes stored in humid environments after blasting, the FBE primer should be applied immediately and the tie layer within the primer’s recoat window as specified by the FBE supplier.

During coextrusion of five-layer LLDPE/EVOH/LLDPE blown films, the tie resin is processed at 215–235°C melt temperature and a die gap between 1.2–2.0 mm. In this structure, OREVAC® C306 is placed as the internal adhesive layer between the LLDPE skin and the EVOH barrier layer; the EVOH layer is commonly 12–25 µm thick and the tie layers are 8–15 µm thick. Adhesion of the tie to EVOH is measured after 24 h conditioning at 23°C and 50% RH under ASTM F904-16; peel values for maleated LLDPE/EVOH systems typically range from 3–8 N/15 mm, but exact grades of EVOH with different ethylene content and melt index can move the failure mode from peeling to film tearing. Moisture on the EVOH layer at the die is a boundary condition: EVOH absorbs moisture during storage, and without sufficient drying in the hopper to below 0.08% moisture, steam bubbles form in the tie layer and reduce contact clarity. Because the tie layer is an internal functional layer, food-contact status is determined by the finished multilayer article; relevant controls include 21 CFR 177.1395 for the laminate structure, 21 CFR 177.1520 for the olefin polymer layers, or 21 CFR 175.105 for adhesive components depending on construction, and Regulation (EU) No 10/2011 with an overall migration limit of 10 mg/dm² unless otherwise specified. The upper service temperature of the film is limited by the onset of seal-bar tack of the LLDPE skin and by the tie layer’s low molecular mobility at deep-freeze conditions below -40°C, where LLDPE-based grafts generally retain better flexibility than HDPE-based versions.

Wood-plastic composite coupling efficiency and moisture-induced hydrolysis in polyethylene-cellulose systems

Wood-plastic composites based on high-density or linear low-density polyethylene and wood flour rely on maleated polyolefins to bridge the non-polar matrix and the polar lignocellulosic filler. In WPC profile extrusion, OREVAC® C306 can be introduced at 2–5 wt% of the total compound with wood flour loadings of 40–60 wt%; the graft reacts with hydroxyl groups on cellulose, hemicellulose, and lignin through esterification or hydrogen bonding, reducing water uptake and increasing flexural strength. Typical processing uses counter-rotating or co-rotating twin-screw extruders with L/D ratios of 30:1–44:1, vented at one or two stages; barrel temperatures are kept between 150°C and 190°C because wood flour begins to emit volatile degradation products and discolour above 200°C. The melt temperature constraint means the LLDPE backbone is a better viscosity match than HDPE for some formulations, but the lower crystallinity also reduces room-temperature modulus. Flexural properties are evaluated under ASTM D790-17; water absorption is tested by immersion per ASTM D570-22. In extruded decking profiles, coupling agents of this class can reduce 24-hour water absorption by 20–40% relative to uncoupled formulations, but published data for OREVAC® C306 in WPC is limited and the exact result depends on wood species, particle size distribution, and venting efficiency. A production failure mode appears when the wood flour moisture exceeds 8% at the throat: the grafted anhydride is partially hydrolysed before it reaches the filler surface, and the exterior surface of the profile develops microcracks. Pre-drying the wood flour to 1–2% moisture or using a heated premixer at 80–100°C is required for continuous profile lines above 300 kg/h output. The combination with amine-containing fire retardants should be avoided because primary amines react with the anhydride and consume the coupling function before it can attach to the wood surface.

For short-glass-fibre reinforced LLDPE compounds, chopped E-glass strands with a nominal length of 4.5 mm are fed into the first side feeder of a co-rotating twin-screw extruder. The maleic anhydride graft in OREVAC® C306 is used at 2–4 wt% of the polymer phase to improve load transfer to the fibres, particularly when the fibre sizing is based on silane and film former chemistries that are compatible with polyolefins. Fibre loadings of 20–30 wt% are common for injection-moulded brackets and housings; tensile strength and modulus are measured according to ISO 527-1:2019 and ISO 527-2:2012. In these systems the grafted LLDPE contributes less to tensile modulus than a maleated HDPE or PP, but it provides better low-temperature impact and lower warpage in flat parts. The main process risk is fibre length reduction during injection moulding; back pressure above 0.5 MPa and screw speeds above 150 rpm intensify fibre breakage, so the compound should be assessed by ashing and fibre-length distribution rather than only by tensile data. Published data for this specific grade in short-glass-filled LLDPE is limited; moulders should first run a 2 wt% starting concentration and compare with the same compound without coupling agent under identical residence time and moisture content below 0.05%.

When the same tie resin is moved from blown film to aluminium composite panel lamination

Aluminium composite panel lamination uses a tie film produced from OREVAC® C306 between a low-density polyethylene core and a pre-treated aluminium skin. The adhesive film is usually 40–80 µm thick and is unwound into a heated roll stack where the aluminium skin and PE core are pressed together at 160–200°C under nip pressures of 2–5 MPa. The maleic anhydride groups interact with the aluminium oxide surface and with the chromate or chromium-free conversion layer; for this reason the aluminium surface must be degreased and conversion-coated immediately before lamination, because natural oxide alone gives lower and more variable peel strength. Peel tests are performed according to ASTM D1876-08 or ASTM D1781-98 when the laminate is subjected to climbing drum peel; commercial aluminium composite panels usually specify a minimum peel strength of 7–10 N/25 mm, but values for this exact grade in a given panel product are not transferable across line configurations. The process window is bounded at the low end by incomplete wetting of the aluminium skin when web speed exceeds 25 m/min and at the high end by the onset of thermal decomposition of the maleic anhydride functionality when the melt temperature exceeds 230°C. Condensation on the aluminium coil must be avoided, especially when the plant is located in high-humidity coastal areas. In the finished panel, the tie layer is not designed to carry structural load; its function is interfacial adhesion, and panel flatness is governed by the LDPE core thickness and the thermal expansion mismatch between the aluminium skins and the polyethylene core.