Influence of surface modification of hydroxyapatite particles on the immobilization onto PET filter fabric

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( School of Textile and Material Engineering, Dalian Polytechnic University, Dalian 116034, China )

InfluenceofsurfacemodificationofhydroxyapatiteparticlesontheimmobilizationontoPETfilterfabric

LIJing,WANGXiao,JIQiang,CUIYongzhu,LYULihua,SONGRuoyuan

(SchoolofTextileandMaterialEngineering,DalianPolytechnicUniversity,Dalian116034,China)

Surface modified hydroxyapatite particles were immobilized onto PET filter fabric via heat fusion method. The influence of esterified modification with methacrylic acid or graft polymerized modification with methyl methacrylate on the immobilization was investigated comparing to pristine hydroxyapatite particles. The effects of treating temperature, time and particle amount on immobilization ratio and pore size ratio of hydroxyapatite-immobilized PET filter fabric using different modification methods were discussed and the adsorption property towards heavy metals was evaluated by cadmium adsorption test. The results showed that higher immobilization ratio, pore size and cadmium adsorption capacity of PET filter fabric were achieved by immobilization of graft modified HAp particles than esterified and pristine HAp particles.

hydroxyapatite; PET filter fabric; immobilization; pore size; adsorption property

0 Introduction

Filter fabrics are widely used in water treatment, food pressing and separation fields[1]. In recent years, heavy metal pollution has been a major concern due to contamination of water, food and serious harm to human health[2-3].

Hydroxyapatite (HAp) is known as a promising heavy metal adsorption agent with special porous structure and high specific surface area[4-5]. The wide application of HAp in water purification is due to its excellent compatibility, extensive sources and low cost[6-7].

In this work, HAp particles were attempted to adhere to the surface of PET filter fabric using heat fusion method[8]. HAp particles were surface esterified with methacrylic acid (MAA) and subsequently surface grafted with methyl methacrylate (MMA) by emulsion polymerization. The immobilization comparison of pristine, esterified HAp (MHAp) and graft modified HAp (PMHAp) under different conditions of heat fusion were investigated. The structure and adsorption property towards cadmium ions were analyzed.

1 Experiment

1.1 Materials and instruments

HAp was supplied by Nanjing Aipurui nanomaterial Co.Ltd. PET filter fabric was provided by Dalian Hualong filter fabric Co., Ltd. Aqueous ammonia, sodium hexametaphosphate, cadmium nitrate tetrahydrate, cadmium nitrate standard solution, acetone, ammonium persulfate, hydroquinone, toluene-p-sulfonic acid, methacrylic acid (MAA) and methyl methacrylate (MMA) were purchased from Tianjin Kermel chemical reagent Co., Ltd.

Ultrasonic pressor (FS-600, Shanghai Shengxi ultrasonic facilities Co.Ltd.) and microfluidics dispersion (M-100P-UL-CE, MFIC company) were used for dispersion.

1.2 Preparation of modified HAp

Esterification of HAp was carried out in acetone at 65 ℃ with 40% of MAA, 0.5% of hydroquinone, 8% of toluene-p-sulfonic acid. MHAp particles were obtained after filtration and washing. PMHAp was obtained via emulsion polymerization of MMA on the surface of MHAp particles initiated by ammonium persulfate in sodium hexametaphosphate aqueous solution of 0.5% under 60 ℃ for 3 h with initiator amount of 12% and a ratio of HAp to monomer of 1∶15.

1.3 Immobilization of HAp onto PET filter fabric

All the samples of PET-HAp, PET-MHAp and PET-PMHAp were fabricated with heat fusion. The mixture of sodium hexametaphosphate aqueous solution and HAp particles was stirred at 25 ℃ for 60 min at pH of 8. The suspension was then treated via ultrasonication of 10 min and micro-fluidic dispersion at 103.4 MPa. Subsequently, HAp suspension was sprayed onto the surface of PET filter fabrics manually. The sprayed PET filter fabrics were dried under 130 ℃ for 5 min. The dried samples were then treated at high temperatures around the melting point of 246 ℃ of PET filter fabric using heat fusion method to immobilize HAp particles.

1.4 Characterization and measurement

Scanning electron microscope (SEM, JSM-6460LV) and X ray diffraction (XRD, D/max-3BX) were applied to observe the surface morphology and structure of samples. Atomic absorption spectrophotometer (HG9600A, Shenyang Huaguang precision instrument Co. Ltd) was utilized to determine the concentration of cadmium before and after adsorption. The immobilization ratio of HAp particles immobilized onto PET filter fabric was calculated according to the following equation:

Immobilization ratio=(m1-m0)/m

(1)

wherem0andm1represent the weight of the PET filter fabric before and after heat fusion treatment, respectively, g;mis the weight of HAp, MHAp and PMHAp, g. Pore size is a key factor affecting filtration efficiency of filter fabrics and it was measured using Bubble pressure test method[9]. Pore size and pore size ratio were calculated from the following formulas:

D=4γ/(Pg-ρgh)

(2)

Pore size ratio=D1/D0

(3)

whereDis the pore size of filter cloth, μm;Pgis the gas pressure, Pa;ρis the density of liquid, g/cm3;handγare the depth of first bubble point to liquid level and the liquid surface tension, respectively, cm, cN/m.D0andD1represent the initial and final pore size of treated PET filter fabric, respectively, μm.

The batch cadmium adsorption experiment was performed at ambient temperature for 24 h at the initial cadmium concentration of 387.7 mg/L. The formulas of cadmium adsorption capacity and removal ratio are written as[10]:

Adsorptive capacity=(ρ0-ρ1)V/m

(4)

Removal ratio=(ρ0-ρ1)/ρ0

(5)

whereρ0andρ1are the initial and final cadmium concentration, respectively, mg/L;Vis the volume of solution, mL;mis the weight of HAp particles immobilized onto PET filter fabric, g.

2 Results and discussion

2.1 Effect of temperature on immobilization ratio and pore size ratio

Effects of temperature of heat treatment on immobilization ratio and pore size ratio of immobilized PET filter fabrics at the particle amount of 20 g/L for PET-HAp and PET-MHAp and 10 g/L for PET-PMHAp for 120 s via heat fusion method are shown in Fig. 1.

It can be seen that the immobilization ratio of PET-HAp and PET-MHAp increased continually with rising temperature until 250 ℃ and little variation was found with further increase of temperature. The effect of temperature on PET-PMHAp differed largely from PET-HAp and PET-MHAp. The sharp increase of immobiliza-tion ratio was observed under 200 ℃. The particles immobilized onto fiber surface caused the decrease of pore size. The variation of immobilization ratio and pore size ratio depends mainly on the difference between heat treating temperature and melting point of PET fiber. Below the melting point, the increasing temperature obviously led to higher immobilization ratio and smaller pore size. When the temperature exceeded the melting point, immobilization ratio was rarely affected. Nevertheless, the ratio of pore size was further decreased. Moreover, the affinity and mobility of PMMA chains on the surface of PMHAp was beneficial to the immobilization of particles at a lower temperature. Particularly, higher immobilization ratio of PET-PMHAp was obtained at a lower amount of HAp particles with the same pore size as PET-HAp and PET-MHAp.

Fig.1 Effect of temperature on immobilization ratio and pore size ratio

2.2 Effect of time on immobilization ratio and pore size ratio

Effects of heating time on immobilization ratio and pore size ratio of PET filter fabric at 250 ℃ for PET-HAp and PET-MHAp and at 240 ℃ for PET-PMHAp at the particle amount of 10 g/L were given in Fig. 2.

In the cases of PET-HAp and PET-MHAp, the immobilization ratio increased and approached equilibrium with a maximum of approximately 40% after continuous heating for 180 s. Nevertheless, the pore size continually reduced with the increasing of heating time. The sustained heating caused slight increase in immobilization ratio and further decrease in pore size as a consequence of the fusion of PET filter fabric as the heating time exceeded 180 s. In contrast, PET-PMHAp gained higher immobilization ratio and larger pore size at a shorter time of 120 s, owing to the fusion and adhesion of PMMA chains on the surface of PMHAp to polyester molecules.

Fig.2 Effect of heating time on immobilization ratio and pore size ratio

2.3 Effect of HAp amount on immobilization ratio and pore size ratio

The dependence of immobilization ratio and pore size ratio of PET-HAp and PET-MHAp treated at 250 ℃ for 180 s and PET-PMHAp treated at 240 ℃ for 120 s on particle amount are shown in Fig. 3. The immobilization ratio of samples increased by 20% as the particle amount ranged from 10 to 50 g/L, while the pore size ratio decreased by about 30%. The relatively slow increase of immobilization ratio implied that the immobilized HAp particles could inhibit further immobilization onto PET filter fabric.

Fig.3 Effect of particle amount on immobilization ratio and pore size ratio

The fusion of PET fibers and immobilized HAp particles gradually decreased with the pore size of filter fabric. Comparatively, more PMHAp particles were immobilized onto the surface of PET filter fabric even under more moderate treating conditions due to higher accessibility of particles to PET fabric under the influence of PMMA chains.

2.4 Surface morphology

SEM micrographs of PET filter fabrics are shown in Fig. 4. HAp or MHAp particles were found to be agglomerate and loosely adhered to the fabric. The well-distributed PMHAp particles seemed to be adhered tightly. The fusion and adhesion of PMMA chains contributed to good immobilization of PMHAp particles onto the surface of PET fabric.

Fig.4 SEM micrographs of PET filter fabrics

2.5 Crystal structure

XRD results of untreated and treated PET filter fabrics are shown in Fig. 5. The diffraction peaks of (002)，(211)，(300)，(310)，(222) and (213) appearing at 25.45°，31.78°，32.54°，39.40°，46.21° and 49.18° were ascribed to HAp particles. The slight shift from 22.82° to 22.72° of diffraction peak (200) of PET suggests that grafted polyester chain could melt with the matrix of PET fibers under heat fusion treatment.

2.6 Adsorption property

As given in Tab. 1, the highest removal ratio of cadmium by PET filter fabric was

Fig.5 XRD patterns of untreated and treated PET filter fabrics

achieved at the highest immobilization ratio. The adsorption property of HAp embedded on the fabric was in the descending order of PET-PMHAp, PET-HAp and PET-MHAp. Esterification of HAp contributed to the enhancement of immobilization ratio, but the entrapment of modified HAp reduced the adsorption property of HAp. However, the higher adsorption property of HAp on PET-PMHAp filter fabric implied that more accessible surface area of HAp particles via fusion and adhesion of PMMA chains to polyester molecules and larger contact area between HAp particles and cadmium ions.

Tab.1 Adsorption property of PET filter fabrics

3 Conclusions

The immobilization of unmodified and modified HAp particles onto PET filter was compared under different treating conditions via heat fusion method. Both PET-HAp and PET-MHAp under an optimal condition of particle amount of 20 g/L, heating temperature of 250 ℃ and heating time of 180 s possessed lower immobilization ratio and pore size than PET-PMHAp treated at the particle amount of 10 g/L at 200 ℃ for 120 s. The esterification of HAp slightly affected the immobilization ratio and pore size, whereas polymerization of MMA on HAp exerted a great influence. The good affinity, fusion and adhesion of PMMA chain resulted in larger immobilization of well-distributed PMHAp particles onto the surface of PET filter fabric and consequently higher adsorption capacity towards cadmium ions.

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羟基磷灰石表面改性对PET过滤布固载效果的影响

李 静， 王 晓， 吉 强， 崔 永 珠， 吕 丽 华， 宋 若 远

( 大连工业大学 纺织与材料工程学院， 辽宁 大连 116034 )

采用热熔法将表面改性的羟基磷灰石固载到PET过滤布上,探讨了未改性、甲基丙烯酸酯化改性和甲基丙烯酸甲酯接枝聚合改性的羟基磷灰石在不同热熔温度、热熔时间和颗粒量条件下对PET过滤布颗粒固载率及孔径大小影响。通过镉离子吸附测试评价了不同方法制备的过滤布对重金属吸附性能。结果表明，PET过滤布固载接枝改性的羟基磷灰石时能获得更高固载率和更大孔径及镉离子吸附量。

羟基磷灰石；PET过滤布；固载；孔径；吸附性能

TS195.6

A

1674-1404(2017)06-0444-05

李静,王晓,吉强,崔永珠,吕丽华,宋若远.羟基磷灰石表面改性对PET过滤布固载效果的影响(英文)[J].大连工业大学学报,36(6):444-448.

LI Jing, WANG Xiao, JI Qiang, CUI Yongzhu, LYU Lihua, SONG Ruoyuan. Influence of surface modification of hydroxyapatite particles on the immobilization onto PET filter fabric (in English)[J]. Journal of Dalian Polytechnic University, 36(6): 444-448.

by: 2016-05-20.

LI Jing(1991-), female, postgraduate; Corresponding author: WANG Xiao(1980-), female, associate professor, E-mail: wangxiao@dlpu.edu.cn.