•Thermal degradation of N, N'-dibutyladipamide and polyamide 66 is carried out in a large-scale experimental setup with nitrogen sweeping.•1-Butylazepane-2,7-dione is identified as a primary ...degradation product and precursor for the secondary degradation products.•Degradation mechanisms centering on the generation and decomposition of 7-membered rings are established for N, N'-dibutyladipamide and polyamide 66.
Thermal degradation of N, N'-dibutyladipamide and polyamide 66 (PA66) was carried out in a large-scale experimental setup with nitrogen sweeping in order to collect elusive degradation intermediates. At a high nitrogen flow rate, 1-butylazepane-2,7-dione was identified as a major degradation product from the thermal decomposition of N, N'-dibutyladipamide. Upon heating, 1-butylazepane-2,7-dione produced cyclopentanone and its derivatives, dibutylurea and a nitrile that constituted the majority of degradation products of N, N'-dibutyladipamide, proving that the 7-membered heterocycle compound is a crucial primary degradation product as well as a precursor for the secondary degradation products of N, N'-dibutyladipamide. Subsequently, chemistry concerning the generation and decomposition of 1-butylazepane-2,7-dione was developed for the thermal decomposition of DBA. On the other hand, hexamethylenediamine, 1,8-diazacyclotetradecane-2,7-dione, cyclopentanone and its derivatives were collected as important degradation products from the thermal decomposition of PA66. In view of the structural similarity between DBA and PA66 and their comparable degradation products, a mechanism centering on the generation and decomposition of a 7-membered ring has ultimately been established for thermal degradation of PA66.
Display omitted
Additive manufacturing (AM) for thermoplastic polymer with the advantages of high specific strength and secondary heating molding has gained wide acceptance in diverse industries. Despite the ...inherent formation defects associated with AM technologies, a new approach called additive friction stir deposition (AFSD) has emerged. While traditionally utilized for metal deposition, AFSD is now being explored for thermoplastic polymers, specifically polyamide 66 (PA66) in this study. To enhance the reliability and efficiency of AFSD for PA66, the novel gradient-parameter-AFSD (GP-AFSD), bidirectional fast cooling-AFSD (BFC-AFSD) and monodirectional fast cooling-AFSD (MFC-AFSD) based AFSD techniques were introduced. Through the BFC-AFSD and MFC-AFSD, successful PA66 depositions with sound surface and interior formation were achieved. The rapid cooling rates and optimized heat balance in BFC-AFSD and MFC-AFSD processes effectively prevented defects like grooves at the top surface of deposition and achieved reliable control of deposition formation. PA66 samples produced under MFC-AFSD demonstrated a tensile strength of 26.9 MPa and E-modulus of 549.3 MPa at room temperature. These findings highlight the potential of AFSD in fabricating large thermoplastic polymer structures with high reliability and efficiency, thus facilitating the practical application of AFSD technology in engineering.
•This research firstly conducts a systematic investigation utilizing solid-state deposition technology of AFSD for depositing thermoplastic.•The novel processes GP-AFSD have proposed to balance heat input by adjusting process parameters layer-by-layer.•The heat input accumulation is eliminated in FC-AFSD, enabling the production of precise and well-formed PA66 deposits.
The research of polymerization kinetics and reaction mechanism on flame-retardant polyamide 66 (FRPA66) is of great significance for its industrial production. Here, FRPA66 is prepared by one-step ...melt polycondensation of nylon 66 salt and a reactive flame retardant DPDA. By exploring the relationship of viscosity-average molecular weight versus reaction time at different polymerization stages, the apparent rate constant of FRPA66 is calculated to be 41.8 dL g−1s−1. Besides, molecular simulation analysis demonstrates that the reaction activation energy of DPDA and nylon 66 salt in pre-polymerization stage is 312.04 kcal/mol, indicating that the pre-polymerization time can be extended to make up for the lack of pre-polymerization power of FRPA66. In the final polymerization stage, reasonable control of releasing pressure and polymerization time can promote the self-condensation of a small part of DPDA, thus improving the molecular weight of FRPA66. Finally, based on the polymerization kinetic and reaction mechanism, FRPA66 containing 5% DPDA can reach V-0 level.
Display omitted
•Copolymerized flame retardant polyamide 66 was prepared by copolymerization.•The apparent rate constant was fitted to analyze the polymerization kinetics.•The reaction path was analyzed from the perspective of molecular simulation to verify the polymerization kinetics.
•A reactive S- & P-containing flame retardant (PDDDS) was designed and synthesized.•The LOI of PA66 with 2% PDDDS increased to 31.6% from 22.7%.•The PHRR, THR, and TSP of PA66-2%PDDDS were depressed ...by 47%, 45.7% and 65.1%, respectively.•PA66-PDDDS has excellent flame retardant both in gas phase and condensed phase.
A sulfur- and phosphorus-containing flame retardant monomer phosphonic diamide, P-phenyl-N, N′-bis(p-sulfanilylphenyl) (PDDDS) was designed, synthesized, and incorporated into polyamide 66 (PA66) through polycondensation to suppress smoke generation upon combustion and achieve satisfactory mechanical properties, a good UL-94 rating (V-0), and a high limiting oxygen index (31.6%). The increased flame retardancy of the PA66-PDDDS copolymer was ascribed to its decomposition into (i) gas-phase P–O and SO2 species scavenging free radicals such as H• and OH• and (ii) condensed-phase products catalyzing the dehydration of PA66 to form char layer. Thus, our work presents a strategy for improving the fire safety of PA66 to significantly expand its practical application value.
Display omitted
•3D printing was used to fabricate Nanohydroxyapatite/Polyamide 66 bone tissue scaffold.•The scaffold shows balanced mechanical property and osteogenic ability.•Scaffold promoted ...endogenous bone regeneration in rabbit patellar bone defects.
The biomaterial requirements for bone tissue repair are extremely strict. It not only requires the biomaterial to have good biocompatibility and biological activity, but also requires sufficient mechanical strength. Polyamide 66 (PA66) and nano-hydroxyapatite (n-HA) have been widely investigated in bone tissue engineering scaffold, however, its composites require further research. In this study, the 3D printing technology was utilized to fabricate personalized n-HA/PA66 bone tissue scaffold. The mechanical properties of n-HA/PA66 composite can be adjusted by configuring different raw material components and applying different porosity. It was found that 50 % porosity n-HA/PA66 composite scaffold showed a uniform porous structure and a compressive strength of 33.9 MPa. The composite scaffold also exhibited excellent biological properties while improving mechanical properties, in vitro cell tests indicated that the 3D printed n-HA/PA66 composite scaffold promoted differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts. In in vivo animal model proved that the scaffold promoted endogenous bone regeneration in rabbit patellar bone defects, with newly formed bone volume of 20.9 % after two months of implantation. This research proposed a 3D printed polyamide/nano-hydroxyapatite composite with balanced mechanical property and osteogenic ability for customized bone tissue repair, and it has promising application prospects.
•Renewable sources have been used to improve the fire performance of PA66.•PA66 composite had good flame retardant and anti-dripping performance.•The generated ammonia of FR-PA66 decreased by 69.4% ...than pure PA66.•Vegetable tanning was expanded to prepare flame retardant and anti-dripping PA66.
Vegetable tanning is an ancient process that uses polyphenols to transform animal hides and pelts into durable and structurally stable leather. Inspired by this, polyamide 66 (PA66) and keratin (Ker) were blended to fabricate a PA66 composite (PA66/Ker) by solution casting, which was then tanned to prepare flame retardant and anti-dripping PA66/Ker composite (FR-PA66). The results indicated that the peak of heat release rate (PHRR) and total heat release (THR) of FR-PA66 decreased by 75.3% and 38.4%, respectively. The limiting oxygen index (LOI) of FR-PA66 reached 29.65% and a UL-94 V-0 rating was obtained. In addition, the char residue of FR-PA66 was 21.6% at 800 °C under N2 atmosphere, indicating good char-forming ability. This work provides a new idea by using renewable biomass keratin and tannin to endow PA66 with flame retardant and anti-dripping performance. The preparation process is simple and feasible, suitable for large-scale preparation.
Display omitted
Chemical recycling provides a promising solution to utilize plastic waste. Here, a catalytic hydrogenative depolymerization of polyamide 66 (PA 66) and polyurethane (PU) was developed. The system ...employed Ru pincer complexes at high temperature (200 °C) in THF solution, and even technical‐grade polymers could be hydrogenated with satisfactory yields under these conditions. A comparison of the system with some known heterogeneous catalysts as well as catalyst poisoning tests supported the homogeneity of the system. These results demonstrate the potential of chemical recycling to regain building blocks for polymers and will be interesting for the further development of polymer hydrogenation.
Sponge it up: A Ru‐pincer complex is developed for the hydrogenative depolymerization of polyamide 66 and polyurethane. The system features high reaction temperature with THF as solvent, and technical‐grade polymers are hydrogenated to give a substantial amount of products. Remarkably, a turnover number close to 1000 is obtained for the hydrogenation of a household kitchen sponge.
Oil-containing materials depend on micropore structures to store lubricating oil. However, the micropore structure, an important component of such materials, is difficult to control. Herein, a porous ...iron-based oil-containing material was successfully prepared via powder metallurgy with TiH2 and polyamide 66 short fiber as dual pore formers. Scanning electron microscopy observations and analyses indicated that the complementary effect of dual pore formers enabled the formation of an interconnected hierarchical pore structure with two pore types, which not only provided abundant oil storage spaces but also facilitated the transfer of oil within the materials. Based on ring-on-block friction and wear tests, the iron-based oil-containing composite presented a low coefficient of friction (about 0.078) under a contact pressure of 1.2 MPa.
•PA 66 SF and TiH2 have a strong complementary effect on the growth of open pores.•PA 66 SF has a tailored size that can serve as a better fiber-like pore template.•A hierarchical pore structure contributes to the oil storage–release performance.•Rapid oil-release behavior can prevent further material deterioration during sliding.
Display omitted
•PA 66 will crystallize from the melt upon cooling at rates less than 1000K/s.•PA 66 undergoes separate high and low temperature ordering processes.•Heating rates above 10,000K/s ...prevent cold crystallization from vitrified state.
Processing of polyamide 66 (PA 66) by injection molding includes cooling of the melt at rates between 100 and 103K/s and its solidification at high supercooling. The kinetics of crystallization at such conditions is unknown and has been evaluated in this work using fast scanning chip calorimetry. Slow cooling of the melt of PA 66 leads to formation of crystals, with the maximum crystallinity being about 30%. It has been found by analysis of the crystallinity as a function of the cooling rate that crystallization is suppressed on cooling faster than about 300K/s. Isothermal analysis of the crystallization rate revealed a bimodal temperature dependence, with maxima obtained at about 165 and 110°C. It is suggested that the observation of two distinct crystallization-rate maxima is related to a change of the nucleation mechanism on temperature variation or the formation of different crystal polymorphs exhibiting different growth rate. The findings provide a fundamental step towards accurately predicting the solidification behavior, the skin–core morphology, and properties of injection moldings of PA 66.
