Abstract
A novel N–P ammonium salt 1,3-propylene glycol diphosphate ester (APGDPE) flame retardant was tersely synthesized under solvent-free condition to lower cotton fabric fire hazard. The APGDPE structure was characterized by 1H NMR, 13C NMR, 31P NMR and IR spectroscopy. The reactive P = O(NH4+)2 and PO(OH)2 groups of APGDPE were successfully grafted into cotton fabric to form P–O–C covalent bond. The limiting oxygen indexes (LOI) of treatment cotton with weight gain rate of 14.7%, 17.2% and 20.8% reach 40–44.5%. After 50 laundering cycles (LCs), the LOI value of treatment cotton with weight gain rate of 20.8% still maintains 27.3%. These results verified that the treated cotton has obtained outstanding flame retardancy and prominent durability. TG test indicates that the thermal stability and thermal oxidative stability of treated cotton are much higher than those of control cotton. TG-IR test displayed that treated cotton released less flammable volatile gases than those of control cotton. Cone calorimetry revealed that the PHRR and THR values of treated cotton decreased by 5.57% and 26.8%, respectively. XRD results suggest that the crystallization zone of cotton fabric before and after treatment hardly change. TG-IR and cone calorimetry tests verified the APGDPE condensation phase mechanism for treated cotton.
Highlights
Natural cotton fabrics contain many hydrophilic hydroxyl groups which havebeen widely applied in the textile industry(Xie et al 2013), and possess the superior properties such as water-absorbing quality, breathability,acceptable physiological comfortableness and excellent mechanical properties which are used extensively in the manufacture of the soft and breathable textile e.g. underwear, hospital healthcare textiles, bedding and sleeping product, military and protective garments, etc.(Gao et al 2015)
Textiles treated with these flame retardants will release carcinogenic formaldehyde during finishing and use(Jia et al 2017).it is necessary to study the formaldehyde free, halogen - free and durable flame retardant for cotton.In addition, in order to further enhance the fire resistance and durability of cotton fabrics, someeffective strategies were implemented by coating(Zhang et al 2019), grafting(Wang et al 2020), layer-by-layer (LBL) self-assembly(Pan et al 2015),plasma treatment(Lam et al 2011) and solgel technology(Periyasamy et al 2020) etc.which can efficiently enhance the cotton fabric fire resistance
The absorption peak at 1697 cm-1was assigned to the stretching vibration of C=O groupsin which the O-H groupsof cotton fabric were partially oxidized(Ortelli et al 2019).The absorption peaks at 1234 and 838 cm-1wereseverally attributed to stretching vibration of P=O and P-OH groupsderived from APGDPE(Zhao et al 2016)
Summary
Natural cotton fabrics contain many hydrophilic hydroxyl groups which havebeen widely applied in the textile industry(Xie et al 2013), and possess the superior properties such as water-absorbing quality, breathability,acceptable physiological comfortableness and excellent mechanical properties which are used extensively in the manufacture of the soft and breathable textile e.g. underwear, hospital healthcare textiles, bedding and sleeping product, military and protective garments, etc.(Gao et al 2015). In this study, using the non-toxic chemical reagents 1,3-propylene glycol and phosphoric acid as reactants, an efficient and environmentally friendly N-P synergistic flame retardant APGDPE was synthesized under solvent-free conditions.Compared with Proban and Pyrovatex CP, APGDPE is halogen-free and does not release formaldehyde.the treatment cotton fabric with weight gain rate of 20.8%can still meet the flame retardant standard after 50 LCs.APGDPE can solve the durability problem of some biological macromolecules. The vertical flammability test of control cotton and treated cotton were tested on the YG815B vertical fabric flame retardancy tester (Nantong Sansi Electromechanical Science & Technology Co., Ltd. China) in accordance with the ASTM D6413-99 test standard. The tensile strengths of the samples were measured on an HD026N electronic fabric tension tester (Nantong Hongda Experiment Instruments Co., Ltd., China) in accordance with ASTM 5035-2006 standard. Air permeability of cotton fabricwas determinedusing an YG (B) 461D-IIair permeability tester in accordancewithTS 391 EN ISO 9237 standard
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