The effects of combined graphene/Fe3O4 nanoparticles on the flame retardancy and smoke suppression of PVC were studied. The dispersion state of graphene in the PVC matrix was improved with the help of Fe3O4 nanoparticles. As a result, the peak values of heat release rate and smoke production rate measured by cone calorimetry were obviously decreased in the PVC/graphene/Fe3O4 composites. According to the results from TGA tests and structural characterization of residual char, the improved flame retardancy was partially attributed to the formation of a network-like structure due to the good dispersion state of graphene in the PVC matrix, and partially to the carbonization of degradation products of PVC catalyzed by Fe3O4 nanoparticles. In addition, ternary PVC composites showed higher mechanical properties than pure PVC. More importantly, the resulting material possessed both electrical and magnetic properties. As a result, the ternary composites showed favorable electromagnetic shielding efficiency in the X-band frequency region (8–12 GHz), due to the formation of conducting interconnected graphene-based networks in the insulating PVC matrix and the magnetic properties.

Several poly(vinyl chloride)-g-polystyrene graft copolymers (PVC-g-PS) with well defined molecular structures were synthesized via atom transfer radical polymerization (ATRP) from the structural defects of PVC. The effects of PS branch chains on the shear and extensional rheology as well as foaming properties were investigated. Compared to linear PVC, the introduction of PS branches results in increased complex viscosity, an elevated value of storage modulus at low shear frequencies, more pronounced shear-thinning behavior, more significant upshifted deviation from linear behaviour and a strain hardening phenomenon. Under the same foaming conditions, most of the resulting PVC-g-PS foams exhibit a closed cell structure, increased cell density and uniform cell size distribution while the linear PVC foam has serious cell coalescence. Moreover, graphene nanosheets could be well dispersed in the PVC-g-PS matrix due to the π–π stacking with PS relative to the PVC without PS branch chains. As expected, both the nucleation effect and increased melt viscosity from well-dispersed graphene sheets significantly improve the foaming behavior of PVC-g-PS/graphene nanocomposites, in comparison with the poor foamability of PVC/graphene composites due to the non-uniform dispersion of graphene.

•The effect of dithiocarbamates on the melt reaction of modified PP is proposed.•The topological structure of the LCBPP depends on the chemical structures of dithiocarbamates.•The proposed mechanism explains the resultant star-like and comb-like topology of the LCBPP.Four dithiocarbamates with different chemical structures (S-Propyl N,N-dipropyldithiocarbamate, S-allyl N,N-dipropyldithiocarbamate, S-Propyl N-pyrrolocarbodithioate and S-allyl N-pyrrolocarbodithioate) were used to adjust the melt radical reaction of polypropylene (PP). The combined effects between activating group Z (N,N-dipropyl and N-pyrrolo) and leaving group R(allyl and propyl) in the dithiocarbamates on melt reaction of PP were studied in the presence of peroxide and trimethylolpropane triacrylate monomer. The results from 1H NMR, FTIR, GPC, rheological measurements and model experiments showed that chemical structures of activating group Z and leaving group R played a key role in the molecular structures and melt properties of modified PP samples. The presence of S-allyl N-pyrrolocarbodithioate with stronger activating group N-pyrrolo and easier leaving group allyl led to the formation of long chain branching structure with more branched points (comb-like topology). The possible reactions in the above systems were also discussed.