Subscriber access provided by UNIV OF REGINA
Article
UV Grafting of a DOPO-Based Phosphoramidate Monomer onto Polyamide 66 Fabrics for Flame Retardant Treatment CHANCHAL KUMAR KUNDU, Bin Yu, Chandra Sekhar Reddy Gangireddy, Xiaowei Mu, Bibo Wang, Xin Wang, Lei Song, and Yuan Hu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04188 • Publication Date (Web): 23 Jan 2017 Downloaded from http://pubs.acs.org on January 24, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
UV Grafting of a DOPO-Based Phosphoramidate Monomer onto Polyamide 66 Fabrics for Flame Retardant Treatment Chanchal Kumar Kundu, † Bin Yu, † Chandra Sekhar Reddy Gangireddy, † Xiaowei Mu, † Bibo Wang, † Xin Wang,*, † Lei Song,† and Yuan Hu*, † †State Key Laboratory of Fire Science, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, P. R. China
ABSTRACT: A novel DOPO-based phosphorus and nitrogen containing monomer named as DOPO-DAAM was synthesized and grafted onto the surface of polyamide 66 (PA 66) fabrics via UV grafting in order to improve the flame retardancy. To facilitate the grafting efficiency, the PA66 fabric surface was first modified through the HCl treatment. In the UL-94 vertical burning test, the PA66 fabric with high DOPO-DAAM content could stop the melt-dripping. Cone calorimetry results showed that a 22% reduction in peak heat release rate was achieved for PA66 fabrics grafted with 20 wt.% DOPO-DAAM. Thermogravimetric analysis indicated that the presence of grafted monomer catalyzed the degradation pathway of virgin PA66 fabrics where the initial decomposition temperature was reduced and the char yield was enhanced for all treated fabric samples. Moreover, real time FTIR analysis confirmed that the DOPO-DAAM decomposed ahead of virgin PA66 and catalyzed the formation of char residue.
1. INTRODUCTION Polyamide 66 (PA 66) is a thermoplastic textile material widely used in many fields including apparels and industrial textiles due to its superior performances such as high mechanical strength, low cost, resistant to shrinkage and pleasant aesthetics. Nevertheless, these materials are highly flammable and also have dripping problems which limit its use in wide range applications.1, 2 Polyamide fibers are relatively hydrophobic in nature and have a low surface energy which makes the processing of such materials quite difficult. Surface modifications or partial degradation of such fibers through the hydrolytic or oxidizing action of chemicals or biological catalysts might create additional reactive functional groups on material surface and that can ease the way of more effective grafting or adherence of coatings in imparting flame retardant or some other functional properties.3 Grafting technology displays superiority over other approaches, such as tunable density of grafting chains and the bulk properties unchanged.4 Over the last few decades, a variety of grafting polymerization techniques have been developed, which can be induced by chemical initiator,5 ion radiation,6 plasma,7 and UV light.8 Among these techniques, UV irradiation is regarded as the most reliable method because it has the lowest probability to weaken bulk properties due to the lower radiation energy.9 The mechanism of photo-induced grafting polymerization involves that radicals is generated while macromolecule is irradiated by UV light in the presence of the photo
initiator, and then photosensitive monomers can be grafted on the surface.10 Previously Liu et al. used acrylamide as a flame retardant for PA 66 fabric through photo grafting and were able to enhance the thermal stability of PA 66 fabrics and simultaneously stop the melt dripping. They also modified PA66 with maleic anhydride by exposing to UV light in association with a post reaction with triethanolamine to enhance the fire retardancy of PA66.11 Grafting of some other monomers like 2-hydroxyethyl methacrylate (HEMA) and allylthiourea in enhancing flame retardant properties of polyamide 66 fabric through microwave induced grafting polymerization were also reported recently.12, 13 Apart from photo-induced graft polymerization, polyallylamine (PAH), sodium polyphosphate (PSP), TiO2 nanoparticles, ammonium polyphosphate, melamine, pentaerythritol and MMT were already used through various techniques by some other research groups in the earlier time in improving the fire retardancy and solving the dripping problems of polyamide fabrics.2, 14, 15 In recent years, developing new halogen-free flame retardants especially some new organophosphorus compounds and their novel derivatives have received increasing interests concerning the environmental sustainability issues.16, 17 Among them, 9, 10- dihydro-9, 10-oxa-10phosphaphenanthrene-10-oxide (DOPO) and its derivatives have received considerable attention due to its flame retardant mechanism in gas-phase which is similar to that of halogenated compounds.17 During the thermal decomposition process, DOPO and its derivatives release active phosphorus-containing fragments which can trap H* and OH* radicals and thus retard the burning process.18
ACS Paragon Plus Environment
Industrial & Engineering Chemistry Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Previous work has demonstrated that DOPO and its derivatives are effective in fire retardant thermosets as well as thermoplastics owing to the relatively high thermal stability, high reactivity and flame-retarding efficiency.19 DOPO-based phosphonamidates with phosphorusnitrogen (P-N) bond are becoming popular for fire retardant application because of the synergistic interactions.20 However, the application of DOPO-based reactive flame retardant for polyamide fabric is rarely reported.21, 22 In the present work, we reported the synthesis of a novel DOPO-based phosphonamidate flame retardant monomer named as DOPO-DAAM and its application on pure PA66 (scoured PA66) and surface modified (HCl treated PA66) fabric through UV-induced graft polymerization. The chemical structure of DOPO-DAAM was characterized by FTIR, 1H-NMR, and 31P-NMR. Grafting process of the monomer onto the surface of PA 66 fabric was monitored by ATR-IR spectroscopy and SEM. The influence of DOPO-DAAM on the thermal and flame retardant properties were also studied and discussed. Furthermore, the thermal degradation process of PA66 fabrics was monitored by real time FTIR and the pyrolysis products were evaluated by thermogravimetric analysis coupled with infrared spectrometry (TGA-IR). 2. EXPERIMENTAL 2.1. Materials. DOPO was provided by Energy Chemicals (Shanghai, China) and di-allyl amine was supplied from Aladdin Reagent Co., Ltd. (Shanghai, China). Triethylamine (TEA), dichloromethane, carbon tetrachloride (CCl4) and acetone were purchased from Shanghai Chemical Reagents Company (China). Benzophenone was used as a photo initiator and the UV irradiation instrument was made by Lantian Co. (China) (80 W/cm2). 100 % PA 66 Woven fabric with the density of 100 g/m2 were obtained from Jiaxing Weaving Industry Co. Ltd. (Yangzhou City, China). The fabric samples were pre-treated with 3 M HCl to obtain better grafting efficiency by increasing the extent of surface functional groups, and finally airdried at ambient temperature. 2.2. Synthesis of DOPO-DAAM. DOPO (43.23 g, 0.2 mol), triethyl amine (31 ml, 0.2 mol) and di-allyl-amine (25 ml, 0.2 mol) were dissolved in 200 ml of dichloromethane and stirred. After the solution was cooled by ice bathing, carbon tetrachloride (20 ml, 0.2 mol) was added drop to avoid that the reaction temperature exceeded 10°C. After completing the addition of carbon tetrachloride, the mixture was heated to room temperature. The resultant triethylamine hydrochloride was filtered off, and then the clear solution obtained was washed with water (100 ml), dried by Mg2SO4 and the solvent was evaporated in vacuum. A slightly yellowish clear liquid was obtained and named as DOPO-DAAM. The synthesis of DOPO-DAAM was illustrated in Scheme 1 and its chemical structure was characterized using FTIR and NMR: 1H-NMR (CDCl3, ppm) 8.04 -7.20 (8 H, aromatic
Page 2 of 12
portion), 5.10 – 5.80 (6 H, -CH=CH2), 3.57 – 3.75 (4 H, CH2). 31P-NMR (CDCl3) δ (ppm): 15.9. FTIR (neat liquid, cm -1), 1640 (C=C), 1274 (P=O), 924 (P-N), 2976 [C-H (s)], 3075 [C=H (v)]. HRMS (ESI-TOF) calculated for [M + 1] C18H18NO2P m/z, 312.1148; found, 312.1154. Scheme 1. Synthetic route of DOPO-DAAM
P
H N
O
P
O
O
O H
N
2.3. Preparation of DOPO-DAAM treated PA 66 fabric by UV-grafting. In the first step, FR monomer was dissolved in acetone with a monomer content (w/v) of 100 (PA 66-10W), 200 (PA 66- 20W), and 300 g/L (PA 6630W) in the presence of 4% (w/w) photo initiator (benzophenone) at room temperature as shown in Table 1. The fabric samples were immersed in 1 mL/g of the FR solution. The fabrics were exposed to the UV light source single-sided for a fixed time in air atmosphere. Then, the fabrics were washed once by a textile linitester to remove un-grafted FR monomer and afterwards dried at room temperature and finally, the sample was dried in an oven until a constant weight. It was proposed that the benzophenone can initiate free radicals on the backbone of PA 66 when exposing to UV light and lead to the copolymerization of the DOPO-DAAM monomer. Table 1. Formulations and dry weight pickup of fabric samples
Sample
FR(g)/acetone(L)
Dry weight pickup (added-on) (%)
SS-PA 66-Control
0
0
SS-PA 66-10W
100
8.21
SS-PA 66-20W
200
15.20
SS-PA 66-30W
300
20.30
HT-PA 66-Control
0
0
HT-PA66-10W
100
9.28
HT-PA66-20W
200
17.27
HT-PA66-30W
300
21.07
Note: SS- Pure scoured sample, HT- HCl treated surface modified sample
2.4. Characterization. The chemical structure of samples was characterized by Nicolet 6700 FT-IR spectrophotometer using KBr disk method.
ACS Paragon Plus Environment
Page 3 of 12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
Real time Fourier transform infrared spectra (RT-IR) was performed on Nicolet 6700 FT-IR spectrophotometer coupled with a ventilated oven. The sample blended with KBr powder was pressed into a disk, and then heated in the oven at a linear rate of 10 °C/min. The IR spectra were collected in situ during the thermal degradation process of the fabrics. 1
H-NMR and 31P-NMR spectra were measured on an Bruker Avance 300 spectrometer. The solvent used was CDCl3. The GC/MS analysis was carried out on an Agilent GC6890 gas chromatograph connected with MS5973 mass spectrometer. The carrier gas was helium. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra were conducted on a Nicolet Avatar 6700 FT-IR spectrophotometer.
3.1. Morphology of the grafted PA66 fabrics. ATR spectra of SS-PA66-Control (a), HT-PA66-Control (c) and DOPO-DAAM-coated fabrics (b, d) are shown in Figure 1. The grafting of DOPO-DAAM monomer onto PA-66 fabrics was confirmed by the vinyl (allyl) characteristic band at 900 cm-1. Compared to spectra a and c, spectra b and d have new peaks around 1200, 1170 and 1157 cm-1, which are attributed to the characteristic peaks of C-C and C-N bonding that confirm the grafting of FR monomer on to the PA66 fabric surfaces. The characteristic bands at 3305, and 1639 cm-1 in the spectra a-d could be ascribed to VN-H, and VC=O, respectively, indicating the presence of the amide group. The combined characteristic bands of both δ NH and VC-N can be still observed for the treated fabric samples, implying very thin thickness of the grafting layer (
