A New Method for Producing High Melt Strength Poly(propylene) with a Reactive Extrusion

Summary: A new class of melt blend material was prepared by extruding a mixture of 3‐aminopropyltriethoxysilane (APTES), maleic anhydride‐grafted poly(propylene) (PP‐g‐MA) with different molecular weight and MA content and poly(propylene) powder produced with a TiCl₃‐based catalyst (PP‐A). A suitable selection of PP‐g‐MA provided extremely high melt strength (MS) of resultant blend materials. Such a superior melt property was caused by the synergy between the present melt reaction and the higher molecular weight portion containing PP‐A. The gel content measurements of typical blend materials and PP‐g‐MA/APTES blends indicated that an excessive amount of inert PP suppresses the formation of gels. The reaction between PP‐g‐MA and APTES was then investigated by analyzing crystalline polymer fractions separated from the atactic PP/PP‐g‐MA/APTES and atactic PP/PP‐g‐MA blends. The FT‐IR analysis of the fractions revealed that the NH₂ group in APTES readily reacts with MA grafted on PP and the reaction leads to the formation of imide linkage. Moreover, the GPC analysis of the fraction showed that higher molecular weight polymers were formed in the presence of APTES. Since a trace amount of water surely produces in the vicinity of active silyltriethoxy groups during the reactive extrusion, such polymers were formed by the condensation between hydrolyzed APTES‐grafted polymer chains. These results led us to the conclusion that long‐chain‐branched PP (LCB‐PP) was certainly produced and its formation is essential for the increase in MS of the present blend materials.

Relationship between log(MS) and log(MFR) for PP/PP‐g‐MA/APTES and commercial PP resins.     

Preparation and thermal conductivities of filled tetrahedral LixIn1−xZnxSb and the related compounds

Li-filling in tetrahedral InSb and related compounds was attempted to investigate its effect on their thermal conductivities. Li-filled Li_0.2In_0.8Zn_0.2Sb, Li_0.4In_0.6Zn_0.4Sb, LiZnSb, and Li_0.16Ga_0.84Zn_0.16Sb sintered samples were prepared by powder metallurgy. The filled samples had much lower room temperature lattice thermal conductivities than those of the corresponding unfilled materials; the values of the Li_0.4In_0.6Zn_0.4Sb, LiZnSb, and Li_0.16Ga_0.84Zn_0.16Sb were 23, 45, and 72 mW cm⁻¹K⁻¹, respectively. Filled tetrahedral compounds such as Li_xIn_1−xZn_xSb might be good thermoelectric materials.     

Amine/epoxy stoichiometric ratio dependence of crosslinked structure and ductility in amine-cured epoxy thermosetting resins

Epoxy-amine thermosetting resins undergo different reactions depending on the amine/epoxy stoichiometric ratio (r). Although many desirable properties can be achieved by varying the stoichiometric ratio, the effects of the variation on the crosslinked structure and mechanical properties and the contribution of these factors to the ductility of materials have not been fully elucidated. This study investigates the brittle-ductile behavior of epoxies with various stoichiometric ratios and performs curing simulations using molecular dynamics (MD) to evaluate the crosslinked structures. The molecular structure is predominantly branched in low-stoichiometric ratio samples, whereas the chain extension type structure dominates the high-stoichiometric ratio samples. As a result, the higher-stoichiometric ratio samples enhances the ductility of materials and the elongation at break increases form 1.4% (r = 0.6) to 11.4% (r = 1.4). Additionally, the tensile strength (105.4 MPa) and strain energy (7.96 J/cm³) are maximum at r = 0.8 and 1.2, respectively. On the other hand, the Young's modulus is negatively impacted and it decreased from 4.2 to 2.7 GPa with increasing stoichiometric ratio.