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<\/p>\nMaleic anhydride grafted polypropylene (MAH-g-PP) is a functionalized polyolefin produced by reactive extrusion grafting of maleic anhydride monomers onto a polypropylene backbone. The resulting polar anhydride groups create chemical bridges between non-polar PP matrices and polar fillers, reinforcements, metals, or engineering resins. In cable manufacturing this delivers measurable gains in interfacial adhesion, mechanical strength, filler dispersion, and long-term electrical stability for both thermoplastic polypropylene insulation systems and highly filled low-smoke halogen-free (LSZH) compounds.<\/p>\n
Typical commercial grades exhibit grafting levels of 0.5\u20132.0 wt% MAH (acid-base titration or FTIR), melt-flow rates of 20\u2013120 g\/10 min (190 \u00b0C or 230 \u00b0C \/ 2.16 kg depending on grade), and densities of 0.90\u20130.92 g\/cm\u00b3. These parameters allow uniform dispersion at low addition levels while preserving processability on twin-screw compounding lines used for cable insulation and sheathing compounds.<\/p>\n
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PE-g-MAH effectively bridges non-polar polyolefins with polar fillers, flame retardants, and engineering resins, resulting in composites with improved tensile strength, elongation, impact toughness, and long-term stability.<\/p>\n
Polypropylene is gaining adoption as a recyclable thermoplastic alternative to cross-linked polyethylene (XLPE) for medium- and high-voltage cable insulation because it can be re-melted and reprocessed. Pure PP, however, shows poor adhesion to polar mineral flame retardants (ATH, MDH), glass fibers, or metallic conductors and exhibits higher space-charge accumulation under DC stress. Grafting maleic anhydride introduces deep traps that suppress space-charge injection and raise breakdown strength while simultaneously coupling the matrix to fillers.<\/p>\n
Laboratory data confirm that PP-g-MAH raises the characteristic DC breakdown strength of polypropylene from approximately 399 kV\/mm to 453 kV\/mm (13.5 % increase) and elevates the critical electric field from 33.5 kV\/mm to 46.7 kV\/mm. Volume resistivity remains in the 10\u00b9\u00b3\u201310\u00b9\u2074 \u03a9\u00b7m range at 70\u201390 \u00b0C, matching or exceeding conventional XLPE under comparable stress.<\/p>\n
During melt compounding the anhydride rings open and form covalent or hydrogen bonds with hydroxyl groups on glass-fiber surfaces, magnesium hydroxide, aluminum trihydrate, or metal oxides. The polypropylene backbone remains compatible with the bulk PP or PP\/PE blend, creating a molecular bridge that transfers stress and prevents filler pull-out or agglomeration. In ternary systems containing epoxy-functional copolymers the anhydride further reacts to generate in-situ PE\u2013PP copolymers that improve creep resistance above the melting point of LDPE while retaining thermoplastic recyclability.<\/p>\n
Grafting is performed by reactive extrusion with peroxide initiators (typically DCP or similar) under controlled temperature (170\u2013200 \u00b0C) and residence time to maximize grafting efficiency while limiting chain scission and residual free MAH. High-quality grades show low odor, low yellowing index, and residual monomer below 0.1\u20130.3 wt%, critical for clean cable extrusion and long-term dielectric performance.<\/p>\n
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<\/div>\n| Param\u00e8tre<\/th>\n | Typical Range<\/th>\n | Test Method \/ Condition<\/th>\n<\/tr>\n<\/thead>\n |
|---|---|---|
| Grafting rate (MAH)<\/td>\n | 0.5\u20132.0 wt% (medium to high)<\/td>\n | Acid-base titration \/ FTIR<\/td>\n<\/tr>\n |
| Melt flow rate<\/td>\n | 20\u2013120 g\/10 min<\/td>\n | 190 \u00b0C or 230 \u00b0C \/ 2.16 kg<\/td>\n<\/tr>\n |
| Density<\/td>\n | 0.90\u20130.92 g\/cm\u00b3<\/td>\n | ASTM D792 \/ ISO 1183<\/td>\n<\/tr>\n |
| Appearance<\/td>\n | Natural translucent pellets<\/td>\n | Visual<\/td>\n<\/tr>\n |
| Residual free MAH<\/td>\n | < 0.3 wt%<\/td>\n | Extraction<\/td>\n<\/tr>\n |
| Recommended dosage<\/td>\n | 1.5\u20135.0 wt% (compound total)<\/td>\n | Application-dependent<\/td>\n<\/tr>\n |
| Processing temperature<\/td>\n | \u2264 280 \u00b0C<\/td>\n | Twin-screw extrusion<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Higher grafting rates improve coupling efficiency but increase melt viscosity and may require adjusted screw design. Lower-MFR grades are preferred for extrusion of thick insulation walls; higher-MFR grades facilitate rapid dispersion in high-filler masterbatches.<\/p>\n Selection and Application Guidelines for Cable Manufacturers<\/h3>\nDosage must be optimized against filler surface area: higher loadings of fine MDH require the upper end of the 3\u20135 % range. Excess compatibilizer can reduce melt strength or introduce unnecessary polarity that elevates dielectric loss at power frequency; therefore laboratory screening of tensile, elongation, volume resistivity, and dielectric loss tangent at 90 \u00b0C is mandatory.<\/p>\n Standards, Failure Modes and Processing Precautions<\/h3>\nRelevant reference frameworks include IEC 60502 \/ IEC 60840 for power cables, GB\/T 12706 for extruded insulation, and material test methods GB\/T 1040, GB\/T 1410, GB\/T 1408. Emerging thermoplastic PP insulation systems are evaluated against the same electrical and mechanical criteria as XLPE while adding recyclability metrics.<\/p>\n Common failure modes prevented by correct use of MAH-g-PP:<\/p>\n
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