Preparation of high melt strength polypropylene by addition of an ionically modified polypropylene

In Situ Nanofibrillar Polypropylene-Based Composite Microcellular Foams with Enhanced Mechanical and Flame-Retardant Performances

With the increasing demand for plastic components, the development of lightweight, high strength and functionalized polypropylene (PP) from a cost-effective and environmentally friendly process is critical for resource conservation. In situ fibrillation (INF) and supercritical CO2 (scCO2) foaming technology were combined in this work to fabricate PP foams. Polyethylene terephthalate (PET) and poly(diaryloxyphosphazene)(PDPP) particles were applied to fabricate in situ fibrillated PP/PET/PDPP composite foams with enhanced mechanical properties and favorable flame-retardant performance. The existence of PET nanofibrils with a diameter of 270 nm were uniformly dispersed in PP matrix and served multiple roles by tuning melt viscoelasticity for improving microcellular foaming behavior, enhancing crystallization of PP matrix and contributing to improving the uniformity of PDPP’s dispersion in INF composite. Compared to pure PP foam, PP/PET(F)/PDPP foam exhibited refined cellular structures, thus the cell size of PP/PET(F)/PDPP foam was decreased from 69 to 23 μm, and the cell density increased from 5.4 × 106 to 1.8 × 108 cells/cm3. Furthermore, PP/PET(F)/PDPP foam showed remarkable mechanical properties, including a 975% increase in compressive stress, which was attributed to the physical entangled PET nanofibrils and refined cellular structure. Moreover, the presence of PET nanofibrils also improved the intrinsic flame-retardant nature of PDPP. The synergistical effect of the PET nanofibrillar network and low loading of PDPP additives inhibited the combustion process. These gathered advantages of PP/PET(F)/PDPP foam make it promising for lightweight, strong, and fire-retardant polymeric foams.

Engineering Polypropylene-Calcium Sulfate (Anhydrite II) Composites: The Key Role of Zinc Ionomers via Reactive Extrusion

Polypropylene (PP) is one of the most versatile polymers widely used in packaging, textiles, automotive, and electrical applications. Melt blending of PP with micro- and/or nano-fillers is a common approach for obtaining specific end-use characteristics and major enhancements of properties. The study aims to develop high-performance composites by filling PP with CaSO₄ β-anhydrite II (AII) issued from natural gypsum. The effects of the addition of up to 40 wt.% AII into PP matrix have been deeply evaluated in terms of morphology, mechanical and thermal properties. The PP-AII composites (without any modifier) as produced with internal mixers showed enhanced thermal stability and stiffness. At high filler loadings (40% AII), there was a significant decrease in tensile strength and impact resistance; therefore, custom formulations with special reactive modifiers/compatibilizers (PP functionalized/grafted with maleic anhydride (PP-g-MA) and zinc diacrylate (ZnDA)) were developed. The study revealed that the addition of only 2% ZnDA (able to induce ionomeric character) leads to PP-AII composites characterized by improved kinetics of crystallization, remarkable thermal stability, and enhanced mechanical properties, i.e., high tensile strength, rigidity, and even rise in impact resistance. The formation of Zn ionomers and dynamic ionic crosslinks, finer dispersion of AII microparticles, and better compatibility within the polyolefinic matrix allow us to explain the recorded increase in properties. Interestingly, the PP-AII composites also exhibited significant improvements in the elastic behavior under dynamic mechanical stress and of the heat deflection temperature (HDT), thus paving the way for engineering applications. Larger experimental trials have been conducted to produce the most promising composite materials by reactive extrusion (REx) on twin-screw extruders, while evaluating their performances through various methods of analysis and processing.

LIonomers-New Generation of Ionomer: Understanding of Their Interaction and Structuration as a Function of the Tunability of Cation and Anion

In this work, by combining maleic anhydride-grafted polypropylene (PPgMA) and three different ionic liquids (ILs), i.e., tributyl (ethyl) phosphonium diethyl phosphate (denoted P⁺DEP), 1-ethyl-3-methylimidazolium diethyl phosphate (denoted EMIM DEP), and 1-ethyl-3-methylimidazolium acetate (denoted EMIM Ac), new ionic PP/IL polymer materials are generated and denoted as LIonomers. The structuration of ILs in LIonomers occurs from a nano/microphase separation process proved by TEM. NMR analyses reveal the existence of ionic-ionic and ionic-dipolar interactions between PPgMA and ILs within LIonomers. The rheological behavior of such IL/polymer combinations interpret the existence of interactions between maleic anhydride group and cation or anion composing the ionic liquid. These interactions can be tuned by the nature of cation (P⁺DEP vs. EMIM DEP) and anion (EMIM DEP vs. EMIM Ac) but also depend on the IL content. Thermal analyses demonstrate that IL could affect the crystallization process according to different pathways. Thanks to the maleic anhydride/IL interactions, an excellent compromise between stiffness and stretchability is obtained paving the way for processing new polyolefin-based materials.

Flame Retardancy Properties and Rheological Behavior of PP/DiDOPO Conjugated Flame Retardant Composites

A bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivative (DiDOPO) with conjugated structure was utilized as a novel conjugated flame retardant, Polypropylene(PP)/DiDOPO conjugated flame retardant composites were papered by being melt-extruding with a twin-screw extruder. The flame retardant efficiency of PP/DiDOPO conjugated flame retardant composites were investigated by cone calorimetry, limiting oxygen index (LOI), vertical burning test (UL-94). Besides, the rheological behavior of PP/DiDOPO conjugated flame retardant composites are measured by ARES rheometer. The results showed that when the content of DiDOPO with conjugated structure was 16 wt%, the LOI values of PP/DiDOPO conjugated flame retardant composites was 24%, and PP/DiDOPO conjugated flame retardant composites reaches V-0 grade. The heat release rate (HRR), total heat release rate (THR) and CO₂ of PP/DiDOPO conjugated flame retardant composites decreased, so PP/DiDOPO conjugated flame retardant composites had excellent flame retardant effect. Rheological analysis results indicated that DiDOPO with conjugated structure suppressed the melt dripping of PP/DiDOPO conjugated flame retardant composites by enhancing the melt stability. The results showed that the DiDOPO with conjugated structure can significantly enhance the flame retardancy effect of PP/DiDOPO conjugated flame retardant composites. In addition, the materials PP/DiDOPO might be with low conductivity and charge transport mobility.