Thermal properties and combustion behaviors of flame retarded epoxy acrylate with a chitosan based flame retardant containing phosphorus and acrylate structure

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Abstract

Functional materials prepared from natural resources arouse a great interest recently. Herein, a novel natural material based flame retardant chitosan phosphate acrylate (GPCS) containing phosphorus and acrylate structure has been prepared. Its effect on thermal properties and combustion behaviors of epoxy acrylate (EA) has been investigated. Microscale combustion calorimeter (MCC) data showed that GPCS reduced the peak heat release (PHRR) and total heat release (THR) of samples greatly, which meant that GPCS was efficient in reducing the flammability of EA. The results of thermogravimetric analysis (TGA) exhibited that GPCS improved the thermal stability of materials at high temperature. Investigation of real time Fourier transform infrared (RT-IR) and thermogravimetric analysis/infrared spectrometry (TGA-IR) revealed that GPCS promoted the formation of char and reduced the release of combustible gas. Thermomechanical properties data showed that the storage modulus of samples increased then decreased with increasing GPCS content while the glass transition temperature continued reduced.

Highlights

► A novel natural material based flame retardant chitosan phosphate acrylate (GPCS) has been prepared. ► We investigated the effect of GPCS on thermal and combustion properties of epoxy acrylate. ► The fire hazards of epoxy acrylate reduced greatly.

Introduction

Functional material prepared from natural resources is an effective way to circumvent the confrontations of pollution, waste disposal and depletion of conventional petroleum-based resources [1], [2], [3], [4], [5]. Much attention has been paid to prepare such materials today [6].

Chitosan, the fully or partially deacetylated form of chitin, the principal component of living organisms such as fungi and crustaceans, one of the most abundant biomaterials in the world, is considered as one of the most studied materials in recent years due to the renewable property, non-toxicity, high biocompatibility and so on. A number of researches focus on its application in clinics, drug delivery systems and surfactants [7], [8], [9]. It should be noticed that chitosan possesses the structure of multi-hydroxyl groups just like pentaerythritol and cyclodextrins, which promote the formation of char during burning [10], [11], [12], [13]. It is well known that the char forming on the surface of the burning materials acts as a heat insulator, limiting the heat transfer from the heat source to the polymer and the mass transfer from the polymer to the flame.

Flame retardant technology develops quickly in decades. The intumescent flame retardant system, composing of acid agent, char forming agent and blowing agent is a focus in recent years owing to its efficiency and environment friendly characteristic. A number of flame retardants have been prepared. However, in these materials, the segment used as char forming source root in petroleum based materials, such as pentaerythritol [14], [15], [16], [17], [18], [19]. Because of the petroleum crisis and the deterioration of ecological environment, it is necessary to search for the replacement of petroleum based materials. Some work has been done on investigating environmental-friendly and sustainable char forming agent, such as starch, lignin and cyclodextrins [20], [21], [22], [23], [24], [25], [26]. But in these researches, the materials were just applied as char forming additives alone. It is well known that flame retardant combining with char former and acid agent in one molecular structure shows higher efficiency on fire resistance [27], [28]. Hence, it is useful to prepare the flame retardant that contain more than one component.

Epoxy acrylate (EA), as a UV curing resin is popular due to its rapid cure, solvent-free characteristics, application versatility, low energy requirements, and low temperature operation [29], [30], [31]. However, it is so combustible that its application is narrowed. A number of methods have been used to improve the fire retardancy of epoxy acrylate and reactive type flame retardant has been proved to be an efficient way because that the flame retardant segments are bonded to the polymer backbone [32], [33], [34], [35].

In this paper, we have prepared a novel chitosan based flame retardant material (GPCS) containing phosphorus and acrylate structure. Herein, phosphorus knowing as one of the most effective flame retardant element was used as acid agent. Acrylate structure was introduced to graft on the backbone of polymer matrix to enhance its compatibility. SEM was applied to reveal the dispersion performance of GPCS in matrix. The characteristic of flammability was presented by MCC. Thermal and mechanical properties were showed by TGA, RT-IR, TGA-IR and DMA.

Section snippets

Materials

Chitosan (viscosity 50–800 mPa s, degree of deacetylation 80–95%), phosphorus pentoxide (AR), methanesulfonic acid (99%) were provided by Sinopharm Chemical Reagent Co., Ltd. Glycidyl methacrylate (GMA), supplied from Dong-fang Chemical Co., Beijing, China, was distilled before used.

Synthesis of GPCS

GPCS can be prepared as the following process. Firstly, phosphorylated chitosan (PCS) can be synthesized by the reaction of chitosan (CS, 2 g) with phosphorous pentoxide (10 g) in methanesulfonic acid in ice water bath

Characterizations of GPCS

FTIR spectra of CS, PCS and GPCS were showed in Fig. 1. For CS, characteristic peak at 1600 cm−1 was ascribed to N-H group. The broad peak observed at 3500 cm−1 has the contribution of the OH group. The other peaks at 2890 and 1380 cm−1 were assigned to CH stretching and CH3 symmetric deformation, respectively. Phosphorylation led to an emerging shoulder at 1200 cm−1, which can be attributed to the Pdouble bondO asymmetric stretching. New peaks at 1050 and 484 cm−1 can be attributed to the Psingle bondO structure, such

Conclusions

A novel chitosan based flame retardant GPCS containing phosphorus and acrylate structure has been prepared successfully. It was applied in EA to improve the thermal properties and reduce the flammability of the matrix. The morphological analysis of the GPCS/EA system revealed that the compatibility between EA matrix and GPCS was good. LOI values increased with the addition of GPCS, indicating that GPCS improved the flame retardancy of EA matrix. MCC data showed the flammability properties of

Acknowledgments

The work was financially supported by the National Basic Research Program of China (973 Program) (2012CB719701), National Natural Science Foundation of China (Grant No. 11125210), National Natural Science Foundation of China (No. 51036007) and the joint fund of NSFC and CAAC (No. 61079015).

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