Study On Modification And Mechanism Of Polyoxymethylene, Polyamide 6, And Recycled Polycarbonate For Improvement In Flame Retardancy, Impact Toughness, And Strength

At present, there are the huge gaps in development of engineering plastics technologies between domestic and international industries. The production scales of general grade engineering plastics are continuously expanding and product categories of general grade engineering plastics are increasing by introducing the complete sets of technique in the domestic enterprises. However, the domestic enterprises lag far behind many countries in the technologies of engineering plastics modification; there are no modified products in market. The almost all domestic market of engineering plastics is monopolized by the foreign enterprises. To promote the improvement of the modification techniques of engineering plastics and the development of the domestic industries, polyoxymethylene(POM), polyamide 6(PA6), and recycled polycarbonate(PC) were modified for achievement of high performance in this work. The studies contain three parts in this paper.Firstly, Preparation and study on flame-retardant mechanism of halogen-free flame-retarded POM compoundsPOM is considered as the most difficultly flame-retarded thermoplastic polymer because of its special chemical structure as well as its thermal stability and chemical degradation characteristics. In this paper, the flammability characteristics and thermal stability of halogen-free flame-retardant POM were studied, and two very effective flame retarding formulation for POM were developed from a combination of ammonium polyphosphate (APP), melamine cyanurate (MC), novolak, and dipentaerythritol(DPER), and the other combination of microencapsulated red phosphorus(MRP), MC, novolak, and DPER. The decomposition behavior of the POM compounds was evaluated by thermogravimetric analysis(TGA). The compound shows optimal flame retardancy with a limiting oxygen index of 52.8 and flammability rating of UL94 V-0, when 27wt.%APP,9wt.%MC,4 wt.% novolak, and 4wt.% DPER are simultaneously incorporated into POM. The MRP/MC/DPER/novolak flame retarded system achieved UL94 V-1 rating. The presence of novolak and DPER as char-forming agents results in a dense and compact multicellular char residue for the test bar after combustion, while Fourier transform infrared(FTIR) spectra confirm a characteristic phosphorous-and carbon-rich char resulting from the APP/MC formulation. The pyrolysis-gas chromatography-mass spectrometry(Py-GC-MS) analysis indicates that highly flammable formaldehyde gas, the main pyrolysis product of POM, is annihilated by amide derivatives produced by the pyrolysis of MC, imparting better flame retardancy. The comprehensive flame-retardant mechanisms based on phosphorus-nitrogen synergism promote the high flame retardancy of POM to reach the non-flammability of the V-0 rating. Secondly, Study on modification of nylon 6 for enhancement of impact resistance and strengthModification of nylon 6 is the focus all the time.This work is focused on a new route to achieve both high fracture toughness and high strength for nylon 6. A series of nylon 6-matrix composites were prepared via melting extrusion by compounding with poly(methyl methacrylate-co-butadiene-co-styrene) (MBS) latex particles as an impact modifier and diglycidyl ether of bisphenol-A (DGEBA) as a compatibilizer. Layered organic montmorillonite and fibrillar wollastonite were also incorporated into the nylon 6 compounds for the reinforcement of materials. Morphology study suggests that the MBS latex particles could achieve a mono-dispersion in nylon 6 matrix with aid of 3wt.% DGEBA, which improves the compatibilization and an interfacial adhesion between the matrix and the shell of MBS using a melt-extrusion technique. A high impact toughness was also obtained but with a corresponding reduction in tensile strength and stiffness. A moderate amount of the layered organic montmorillonite and fibrillar wollastonite as a nonofiller could gain a desirable balance between tensile strength and toughness of the materials, and the flexural strength, tensile strength, and stiffness achieved an improvement. The thermal stability and thermal resistance were also enhanced. This suggests that the combination of nanofillers and core-shell latex particlesis a useful strategy to optimize and enhance the properties of PA6. The structure and morphology of the nanocomposites studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the layered organic montmorillonite was exfoliated within nylon 6 matrix. It was found that the core-shell latex particles and the nanofillers were dispersed respectively in the nylon 6 matrix. The study indicates that the presence of the nao fillers in the nylon 6 matrix cannot disturb the latex particles to promote high fracture toughness via particle cavitation and subsequent matrix shear yielding, in addition, provided maximum reinforcement to the polymer. Thirdly, Study on modification and mechanism of recycled PC in improvement in impact resistance and flame retardancyPC is one of the most important engineering thermoplastics used in a wide variety of applications; the annually consumed amount of this polymer exceeds several million metrictons. In recent years, the interest in recycling of PC has expanded dramatically and this is a trend that will undoubtedly continue into the future, which may be explained by (i) limited natural resources, (â…±) rising waste-handling costs, and (â…²)environmental regulations related to land-filling and incineration of plastics. In this paper, two types of core-shell structured latexes, poly(methyl methacrylate-co-butadiene-co-styrene) (MBS) and poly(methyl methacrylate-co-methylphenyl siloxaneco-styrene) (MSiS) were used to modify recycled polycarbonate(PC) for the enhancement of toughness and flame retardancy. The impact strength of the modified PC blends was not improved after melt-blending recycled PC with these two kinds of latexes, probably because the latex particles were not evenly dispersed in the PC matrix because of the incompatibility between PC and PMMA shell of the latexes. Addition of a compatibilizer, e.g. DGEBA, SMA, or Phenoxy can effectively enhance the toughening effect of recycled PC with core-shell structured modifiers. The presence of compatibilizer in the blends reduces the interfacial tension and introduces a steric hindrance to coalescence, and thus enhances the interfacial adhesion between PC domain and PMMA shell, and improves the dispersion of core-shell structured particles in the PC matrix. The ternary blends achieve a high impact resistance by cavitation of the particles, which relieves the triaxial stress and promotes massive shear yielding of the matrix, and then enables the matrix to fracture by the plane stress ductile tearing mode. Additionally, MSiS has a silicone-based core and can effectively retard the combustion of recycled PC. The blends containing 7wt.% MSiS and 3wt.% compatibilizer can achieve a UL94 V-0 rating in vertical burning test. We proposed that, during combustion, a fine dispersion of MSiS particles in the PC matrix facilitates the rapid migration of MSiS and formation of a uniform and highly flame resistant char barrier on the surface of the modified PC.