Synthesis Of Flow Modifiers And Its Application In Highly Filled Magnesium Hydroxide/Linear Low-Density Polyethylene Composites

Highly filled composites?>40 vol%filler?have been used in many areas?e.g.,electrical and thermal conductive,magnetic,flame retarded,thermostable,ceramic and piezoelectric polymer-based composites?.However,the high loading of fillers inevitably brings about the poor processability,and the production rate and mechanical properties of this type of composite materials have to be rather low and poor,respectively.It remains a great challenge to improve processability without deteriorating or even increasing mechanical properties?especially toughness?at the same time.Based on the low surface energy of fluorinated polymers,they tend to be located at the interface between inorganic fillers and polymer matrix?on the surface of fillers?,reducing the agglomeration of fillers and improving the processability of polymer-based composites.In this work,several fluorine-containing flow modifiers were synthesized by high efficient and simple synthesis method,and were applied to highly filled magnesium hydroxide?MH?/linear low density polyethylene?LLDPE?composites?the weight ratio of MH to LLDPE is 80:20,and the volume ratio is approximately 60:40?,and these flow modifiers simultaneously improved the processability and toughness of highly filled MH/LLDPE composites.The chemical structure of fluorinated polymers was analyzed by Fourier transition infrared spectroscopy?FTIR?and nuclear magnetic resonance?NMR?.The effect of fluorine-containing flow modifiers on the dispersion of MH particles in LLDPE matrix was analyzed by SEM.The effect of fluorine-containing flow modifiers on the processability of MH/LLDPE composite was characterized by torque rheometer and rotational rheometer,and the dynamic rheological property of MH/LLDPE composites was also assessed.Meanwhile,their effect on improving the flame retardancy of MH/LLDPE composites was investigated by thermogravimetric?TGA?,limiting oxygen index?LOI?and vertical burning behavior?UL-94?.The flame-retardant mechanism of fluorine-containing flow modifiers in the highly filled MH/LLDPE composite was also proposed.1. Fluorine-containing flow modifiers with glass transition temperatures higher than 50°Cwere successfully synthesized using hexafluorobutyl methacrylate and methyl methacrylate as co-monomers,which simultaneously improved the processability and toughness of highly filled MH/LLDPE composites.When 5 wt%of the flow modifier PMF11?from equimolar ratio of two monomers?was added to MH/LLDPE composite,and the torque value was decreased by32.2%.Moreover,the impact strength was significantly improved by 63.2%and the flexural properties remained almost constant.The fluorine-containing flow modifiers with low surface energy were located at the interface between LLDPE matrix and MH particles,and weakened the interaction between MH particles,which reduced agglomeration and improved the dispersion of MH particles in LLDPE matrix.The flow modifiers facilitated the relative sliding of MH particles,and reduced the entanglement density and the relaxation time of molecular chains.2. The successfully synthesized flow modifier?Si-DPF?with flame-retardance was locatedat the interface between MH particles and LLDPE matrix to form a core-shell structure with MH particles as core and Si-DPF as shell,which enhanced the dispersion of MH particles,improved processability of MH/LLDPE composites,and reduced the melt equilibrium torque by 48.9%at 5 wt%loading.Meanwhile,the corresponding elongation at break,the area under the stress-strain curves and the notched impact strength were 16,9.1 and 4 times those of the baseline MH/LLDPE composite,respectively.When samples were subjected to external force,Si-DPF effectively transferred energy to the MH particles,thereby inducing a large shear yield deformation and absorbing a large amount of energy.Furthermore,Si-DPF enhanced the flame retardancy of MH/LLDPE composites.The LOI value of MH/LLDPE composite was increased to 63.8%and the residue was also increased by introduction of 5 wt%Si-DPF.It was suggested that Si-DPF mainly promoted the dense char formation,which protected the materials from further degradation.3. A flow modifier PSi F with the comb structure was successfully synthesized via emulsion polymerization.The initial decomposition temperature(T_5%)of flow modifier PSi F was 248°C,which extended its application range.By the wetting coefficient of PSi F and the SEM analysis of samples,the flow modifier PSi F with low surface energy was located at the interface between the MH particles and LLDPE matrix,which improved the dispersion of MH particles in LLDPE matrix and reduced the friction between the MH particles.At 5 wt%loading of PSi F,the melt equilibrium torque of MH/LLDPE composite was decreased to 18.5 N·m,which was decreased by 37.9%compared to that of baseline MH/LLDPE composite.The corresponding elongation at break was increased by 1.5 times,the area under the stress-strain curves was increased by 1.4times and the notched impact strength was increased by more than 2.5 times.4. Fluorine-containing flow modifier HCPCPF with excellent flame retardancy was successfully synthesized from hexachlorocyclotriphosphazene.The SEM analysis showed that HCPCPF was located at the interface between the MH particles and LLDPE matrix,which significantly enhanced the dispersion of MH particles in LLDPE matrix.The torque value of the MH/LLDPE composite with 1 wt%HCPCPF?19.0 N·m?is less than that of the baseline MH/LLDPE?29.8 N·m?,which was decreased by 36.4%.In addition,the toughness of the MH/LLDPE composite was also obviously improved and the flexural properties remained almost constant.Furthermore,HCPCPF enhanced the flame retardancy of MH/LLDPE composites.The LOI value of MH/LLDPE composite was greatly increased to 65.6%by introduction of 5 wt%HCPCPF.It was suggested that HCPCPF played a flame retarded role in the condensed phase by forming a compact char layer,which isolated the heat source and protected the matrix.