H. Keskkula

Nylon 6 nanocomposites : the effect of matrix molecular weight

Organoclay nanocomposites based on three different molecular weight grades of nylon 6 were prepared by melt processing using a twin screw extruder. Mechanical properties, transmission electron microscopy, wide-angle X-ray diffraction, and rheological measurements were used to characterize the three types of composites. Tensile modulus and yield strength were found to increase with increasing concentration of clay, while elongation at break decreased. Izod impact strength was relatively independent of clay content for the higher molecular weight composites, but slightly decreased with increasing clay content for the lowest molecular weight polyamide. In general, nanocomposites based on the higher molecular weight polyamides yielded superior composite properties, having higher degrees of clay exfoliation, higher stiffness and yield strength values, and marginal loss of ductility as compared to nanocomposites based on the low molecular weight polyamide. Differences in properties between the three types of composites were attributed to differences in melt rheology. Capillary and dynamic parallel plate data revealed sizeable differences in the levels of shear stress between each nanocomposites system. A mechanism for exfoliation during melt mixing is outlined.

Effect of organoclay structure on nylon 6 nanocomposite morphology and properties

Abstract A carefully selected series of organic amine salts were ion exchanged with sodium montmorillonite to form organoclays varying in amine structure or exchange level relative to the clay. Each organoclay was melt-mixed with a high molecular grade of nylon 6 (HMW) using a twin screw extruder; some organoclays were also mixed with a low molecular grade of nylon 6 (LMW). Wide angle X-ray scattering, transmission electron microscopy, and stress–strain behavior were used to evaluate the effect of amine structure on nanocomposite morphology and physical properties. Three surfactant structural issues were found to significantly affect nanocomposite morphology and properties in the case of the HMW nylon 6: decreasing the number of long alkyl tails from two to one tallows, use of methyl rather than hydroxy-ethyl groups, and use of an equivalent amount of surfactant with the montmorillonite, as opposed to adding excess, lead to greater extents of silicate platelet exfoliation, increased moduli, higher yield strengths, and lower elongation at break. LMW nanocomposites exhibited similar surfactant structure-nanocomposite behavior. Overall, nanocomposites based on HMW nylon 6 exhibited higher extents of platelet exfoliation and better mechanical properties than nanocomposites formed from the LMW polyamide, regardless of the organoclay used. This trend is attributed to the higher melt viscosity and consequently the higher shear stresses generated during melt processing.

Rubber toughening of polyamides with functionalized block copolymers: 1. Nylon-6

Abstract The toughening of nylon-6 using triblock copolymers of the type styrene-(ethylene- co -butylene)-styrene (SEBS) and a maleic anhydride (MA) functionalized version (SEBS- g -MA) is examined and compared with a conventional maleated ethylene/propylene elastomer. The changes in rheology, adhesion, crystallinity, morphology and mechanical behaviour associated with the reaction of the anhydride with the nylon-6 are documented. Combinations of the SEBS and SEBS- g -MA elastomer blends with nylon-6 give higher levels of toughening than is achieved with the functionalized elastomer alone. The particles of pure SEBS were about 5 μm in diameter (too large for toughening nylon-6), whereas SEBS- g -MA alone yielded particles of about 0.05 μm (apparently too small for optimal toughening). Combinations of the two types of elastomers gave a continuously varying particle size between these extreme limits. This suggests that the two rubbers form essentially a single population of mixed rubber particles. The order of mixing did not significantly affect the mechanical properties of these ternary blends. The evidence for maximum and minimum rubber particle sizes that can be effective for toughening nylon-6 is discussed.

REACTIVE COMPATIBILIZATION OF BLENDS OF NYLON 6 AND ABS MATERIALS

Abstract Blends of nylon 6 with various ABS materials including its styrene/acrylonitrile, SAN, matrix component were examined for rheological behaviour, mechanical properties, and phase morphology. These mixtures have poor mechanical properties unless properly compatibilized. This was done here by adding to the SAN phase a polymer that is miscible with it but which contains functional groups that can react with the nylon 6 to form in situ , graft copolymers at the polymer-polymer interfaces. These compatibilizer molecules contained either anhydride or oxazoline units for reactivity. Evidence of reactions in the blends was seen in the rheological behaviour of the melt and in the morphology and mechanical behaviour of the solid. Some blends exhibited outstanding toughness. A more quantitative assessment of the extent of reaction was provided by a selective solvent extraction technique. Lap shear adhesion measurements for laminates of nylon 6 with materials containing reactive polymers provided a direct way to assess the effectiveness of the interfacial reaction.

Compatibilization of PBT/ABS blends by methyl methacrylate-glycidyl methacrylate-ethyl acrylate terpolymers

Abstract Poly (butylene terephthalate), PBT, can be impact modified by blending with appropriate ABS materials within a limited range of processing conditions. The morphology of these uncompatibilized blends is unstable; the dispersed phase coarsens when the melt is subjected to low shear conditions, e.g. during certain moulding conditions, which has a deleterious effect on the final blend properties. Terpolymers of methyl methacrylate, glycidyl methacrylate (GMA), and ethyl acrylate have been synthesized and shown to be effective reactive compatibilizers for blends of PBT with styrene-acrylonitrile copolymers (SAN) or ABS materials as revealed by improvements in SAN or ABS dispersion and morphological stability. Evidence for reaction between the carboxyl endgroups of PBT and the epoxide groups of GMA during melt processing to form a graft copolymer is presented. The effect of terpolymer composition and content on morphology generation and stabilization of PBT-SAN blends has been examined in depth. Moderate amounts of GMA in the terpolymer (>5%) and small amounts of compatibilizer in the blend (

Morphology of nylon 6/ABS blends compatibilized by a styrene/maleic anhydride copolymer

Abstract Transmission electron microscopy (TEM) was used to examine the morphologies of nylon 6/ABS blends compatibilized with a styrene/maleic anhydride (SMA) copolymer containing 25% maleic anhydride (SMA 25). Several staining techniques were employed for identifying the various phases. The morphologies of a nylon 6/ABS blend compatibilized with an imidized acrylic polymer and the commercially available Triax™ material were also examined by these TEM techniques. While increasing concentration of the SMA 25 copolymer clearly leads to more efficient dispersion of the ABS phase, there is an optimum level of SMA 25 to achieve maximum toughness. Various factors that might contribute to the subsequent loss in toughness with higher SMA 25 levels are discussed. It is concluded that the limitations of the SMA 25 copolymer as a compatibilizer stem mainly from its high level of reactive functionality.

The role of matrix molecular weight in rubber toughened nylon 6 blends: 1. Morphology

Abstract The effects of polyamide molecular weight on morphology generation in nylon 6 blends with maleated elastomers are described. The elastomers used include styrene—butadiene—styrene block copolymers with a hydrogenated mid-block, SEBS, and versions with X % grafted maleic anhydride, SEBS-g-MA- X %, and an ethylene/propylene copolymer, EPR, and a maleated version EPR-g-MA. The molecular weight of the nylon 6 phase governs the melt viscosity of the blend matrix and the number of amine end groups available for reaction with the maleic anhydride groups in the rubber phase; both of which influence the size, shape, and size distribution of the rubber phase formed during blending. In general, rubber particle size, distribution, and the amount of occluded material in the rubber phase decreases as the nylon 6 molecular weight increases. Measurement of the extent of reaction between the amine end groups and the grafted maleic anhydride revealed that a higher fraction of nylon 6 chains are grafted to the rubber matrix as the nylon 6 molecular weight increases. The weight average rubber particle size and size distribution for blends based on SEBS-g-MA- X % are smaller than corresponding blends based on SEBS/SEBS-g-MA-2% mixtures containing the same amount of maleic anhydride. EPR/EPR-g-MA mixtures produce non-spherical morphologies that are typically larger and more polydisperse than SEBS type elastomers. One reason for this difference is the fact that SEBS elastomers react more readily with nylon 6 than do EPR/EPR-g-MA mixtures as determined by extent of amine reaction and torque rheometry. The weight average rubber particle size for blends of the various rubbers and nylon 6 materials were correlated using a modified Taylor theory analysis. A master curve was generated by determining shift factors needed to superimpose the maleated rubber/nylon 6 curves onto a reference curve for the non-maleated rubber, SEBS. The overall shift factors correlate linearly with the maleic anhydride content of the rubber phase.

Compatibilization of nylon 6/ABS blendsusing glycidyl methacrylate/methyl methacrylate copolymers

Abstract Blends of nylon 6 with acrylonitrile/butadiene/styrene (ABS) materials and with its styrene/acrylonitrile copolymer (SAN) matrix were prepared using a series of glycidyl methacrylate/methyl methacrylate (GMA/MMA) copolymers as compatibilizing agents. These copolymers are miscible with SAN and the epoxide unit in GMA is capable of reacting with the polyamide end groups. This copolymer thus has the potential to form graft copolymers at the polyamide/SAN interface during melt processing. This study focuses on the effects of functionality and concentration of the compatibilizer on the rheological, morphological, and mechanical properties of these blends. In general, incorporation of this compatibilizer does not significantly improve the impact properties of nylon 6/ABS blends. In these blends, nylon 6 was always the continuous phase; TEM photomicrographs indicate that incorporation of the compatibilizer results in two distinct populations of ABS domains: large agglomerates, and small dispersed particles. The agglomerates become larger with increasing GMA content in the compatibilizer and result in a non-uniform distribution of rubber particles within the nylon 6 matrix. Torque rheometry was employed to identify the reaction mechanisms that may be responsible for the development of such morphologies. These experiments demonstrate that the cause of the poor ABS dispersion is the difunctionality of the nylon 6 end groups with respect to the epoxide group of GMA, which leads to cross-linking-type reactions.

Impact modification of poly(butylene terephthalate) by ABS materials

Abstract Poly(butylene terephthalate), PBT, can be impact modified by blending with appropriate ABS materials. The effect of ABS type and processing conditions on the notched Izod impact strength of PBT blends is examined in depth. Of three emulsion-made ABS materials containing 38 to 50% rubber, the one with the highest melt viscosity (50% rubber and a broad rubber particle distribution) proved the least effective for improving the impact strength of PBT when processed at high temperatures (260°C). Blends prepared in twin screw vs a single screw extruder have similar impact behavior. Melt temperatures greater than 240°C used during molding have little effect on the crystalline behaviour of PBT; however, they reduce the effectiveness of some ABS grades for impact modification. Blends moulded at higher temperatures show a coarse phase morphology with large, poorly dispersed ABS domains. PBT/ABS blends can have excellent mechanical properties in the absence of any compatibilizer; however, a compatabilizer would no doubt improve the stability of the morphology of the blends and may lessen their dependence on process conditions.

Impact-modified nylon 6/polypropylene blends: 1. Morphology-property relationships

Abstract Two types of elastomers grafted with maleic anhydride (MA), an ethylene—propylene random copolymer (EPR) and a styrene—ethylene/butylene—styrene triblock copolymer (SEBS) were found to function both as impact modifiers and compatibilizers for nylon 6/polypropylene blends. The maleic anhydride grafted to the rubber reacts with the amine end-groups of the polyamide, forming a rubber-nylon 6 graft copolymer that locates at the interface between nylon 6 and polypropylene (PP) and thus acts as a compatibilizer. The SEBS-g-MA material appears to be the most effective compatibilizer. The two rubbers were equally effective for increasing room temperature toughness by dispersing in the nylon 6 phase of the blends. Lower ductile-brittle transition temperatures are obtained when EPR-g-MA rubber is used, owing to its lower Tg and lower modulus at low temperatures compared to SEBS-g-MA rubber. Blend parameters such as rubber content, nylon 6/PP ratio and molecular weight of the components strongly influence the morphology and toughness of the blends. Low ductile—brittle transition temperatures were obtained for blends in which any combination of the above parameters yielded a morphology where nylon 6 was the matrix phase with polypropylene and rubber finely dispersed in it, provided the component molecular weights were high enough to provide adequate intrinsic ductility.