Abstract
Polyketones (PKs) having strong hydrogen bonding properties and a chain extender are used as additives in the melt processing of nylon 6 (PA6). Their effect on the chain structure and properties of PA6 is studied to enhance the processability of PA6 in melt processing. The addition of the chain extender to PA6 increases the melt viscosity by forming branches on the backbone. The addition of PKs results in an additional increase in viscosity through the hydrogen bonding between N–H of PA6 and C=O of PK. The change in the N–H bond FT-IR peak of PA6 and the swelling data of the PA6/PK blend containing a chain extender, styrene maleic anhydride copolymer (ADR), suggest that incorporation of chain extender and PK in the melt processing of PA6 results in physical crosslinks through hydrogen bonding between the branched PA6 formed by the addition of chain extender and PK chains. This change in the chain structure of PA6 not only increases the melt strength of PA6 but also increases randomness resulting in decreased crystallinity.
Highlights
Once the torque stabilized after the addition of PK, the torque was higher compared with that of PA6 alone, which was due to the higher melt viscosity of PK
The time at which the torque started to increase decreased with increase in the PK content. This shows that the epoxy groups of the chain extender anhydride copolymer (ADR) and –COOH or –NH2 groups of PA6 reacted to form branches on PA6 (Figure 2b), and physical crosslinks were formed between the branched PA6 and PK chains through hydrogen bonding interaction (Figure 2c)
Chain extenders used widely in the melt processing of polymers and PK capable of hydrogen bonding were added in the melt processing of PA6, and their effects on the chain structure and properties of PA6 were studied
Summary
Polyamide is the most widely used thermoplastic polymer among engineering plastics due to its superior mechanical properties and chemical resistance [1,2,3]. PA6 automotive parts are generally processed by melt processing such as extrusion or injection molding, and for thermal stability, chain extenders can be used to introduce branches and increase the molecular weight [9,10,11]. As the extrusion or injection molding of PA6 is carried out at a relatively high temperatures above 220 ◦ C, chain scission by thermal degradation results in a decrease in the molecular weight [14], and the melt strength and mechanical properties of the product are decreased significantly. PK having –C=O groups in the main chain capable of forming strong hydrogen bonds is reported to be very compatible with PA6 in melt processing due to its hydrogen bonding with the –NH bonds of PA6 [23,24,25,26] This hydrogen bonding is expected to affect the chain structure of PA6 and the overall properties, there is no report emphasizing this aspect. The effect on the chain structure of PA6 and the resulting change in the rheological and mechanical properties are studied
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