Hydrophilic Modification Of Electrospun Pet Poly Nanofiber Membranes Biology Essay

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Different methods for polymer surface modification have been proposed to obtain more biocompatible polymer materials, including the immobilization of polymer chains onto a polymer surface by coupling reactions and the graft polymerization of monomers via glow discharge, corona discharge, UV radiation, and plasma. In particular, ozone-induce surface grafting is being widely applied in biomaterial research because it has the advantage of uniformly introducing peroxides onto the polymer surface even with complicated shapes and is an easy-to-handle, inexpensive technique. Peroxides are mainly formed, in addition to carbonyl and carboxyl groups, when a polymer is exposed to ozone gas. The generated peroxides are capable of initiating the radical polymerization of vinyl monomers, which results in surface-grafted polymer chains. (Ozone-Induced Grafting of a Sulfoammonium Zwitterionic Polymer onto Low-Density Polyethylene Film for Improving Hemocompatibility)

Surface ozonization is being widely applied in polymer research areas because it has an advantage of uniformly introducing peroxides on the polymer surface even with complicated shape and offers an easy-to-handle, inexpensive technique. When polymer is exposed to ozone gas, peroxides are mainly formed in addition to the carbonyl and carboxyl groups. The generated peroxides are capable of initiating polymerization of vinyl monomers, resulting in polymer grafting onto the ozonated polymeric materials. In this work, it is the first time to graft MPC polymer onto the surfaces of silicone film by ozonization to improve antithrombogenicity of silicone surfaces. The surfaces of the modified film were characterized by XPS, ATR-FTIR, and static contact angle. Also, the blood compatibility of MPC polymer grafted film was evaluated by platelet adhesion study.( Ozone-induced grafting phosphorylcholine polymer onto silicone film grafting 2-methacryloyloxyethyl phosphorylcholine onto silicone film to improve hemocompatibility)

PET fibers are high performance fibers with high strength, high modulus, thermal shrinkage and low price. The PET nanofiber films manufactured by electrospinning are not noly widely used for clothing, filter material, tissue scaffolds, but also can be applied in polymer lithium ion batteries as supporters for polymer electrolyte.

Electrospun membranes are used in a variety of applications, including filtration systems and sensors for chemical detection, and have attracted increased interest in the field of tissue engineering and regenerative medicine.


Materials and reagents

1. Purification and Preparation of samples.

The PET nanofiber films samples were cut into squares from an electro-spun PET film (self-made). Prior to use, the samples were first swelling for 2days in acetone and then washed with ethanol to remove acetone, finally rinsed with distilled water.

PET nanofiber films were cut into pieces for using as specimen in surface modification experiments. The specimen were washed with acetone in an ultrasonic washer and dried at room temperature under vacuum prior to use.

The PET films samples were cut from a commercial PET film (1 mm thick, WeberMe taux) either as squares (10 _10 mm) of 0.03 g or as disks (16 mm diameter) of 0.055 g. Prior to the grafting, PET films were washed for 15 min in tetrahydrofuran (THF) and then twice rinsed with bi-distilled water. The samples were dried under vacuum at 65 C. The sodium salt of styrene sulfonate (NaSS) (Fluka) was purified by recrystallization in a mixture of H2O/ethanol (90/10). Typically 20g of NaSS were dissolved in 500 mL of the mixed solvent at 70 C, then filtrated under vacuum and kept at 4 C for 24h. Recrystallized NaSS was then dried under vacuum at 50 C and kept under argon atmosphere at 4 C prior to the experiment.

Acrylic acid(AAc) was purified by distillation before use

Ferrisulphas (ferrous sulphate) , Toluene, Acetone, ethanol were used as received.

2. Swelling of PET ( Pretreatment of PET )

The graft polymerization system is heterogeneous, reactants participate in the reaction involve liquid monomer and solid state matrix. In order to make the liquid reactant can more easily spread into the internal structure of solid material, it is necessary to swell the PET films matrix.

3. Ozonation.

Ozone was generated from pure oxygen exposed to high voltage (OZONAIR). Optimal conditions of ozonation were found to be as follows: room temperature, 3 L min-1 oxygen and 200 mA. Under these conditions, it was assumed that the ozone concentration in aqueous solution can reach unknown% (v/v). Six PET films samples were placed in various solutions : toluene ,acetone and ethanol. And then exposed to the ozone flow for times varying from 15 to 40 min.

The ozone was generated by an ozone generator using pure oxygen gas as illustrated in Fig.1.

The film was treated with ozonization in a glass vessel

4.Grafting Polymerization

PET nanofiber films were grafted by a radical polymerization initiated by the peroxides generated during the ozonation step. To determine the optimal grafting conditions the following parameters were varied: ozonation time, polymerization method and temperature.

Graft polymerization of acrylic acid onto the PET films was carried out under an nitrogen atmosphere. Immediately after the ozonation treatment each PET sample was placed in a glass reactor containing 3mL acrylic acid solvent (of an acrylic acid aqueous solution with a concentration of 5 to 15% (v/v)). The reaction was carried out at 45 C for 3h. Then, the sample was removed and extensively washed with bi-distilled water for 1 h.

The hydrophilicity of grafted PET film increased with increasing concentration of AAc monomer.

Surface characterization or Grafting Characterization

Contact angle

Static water contact-angle measurements were carried out to investigate the hydrophilicity of the surface of the PET and PET-g-PAAc film. The results summarized in Table suggest that the PET film was relatively hydrophobic, and the hydrophilicity of the grafted film increased with increasing AAc concentration. This also indicated that the graft polymerization took place in higher yields.


(1)Origin (2)ozonized for 20 40 min (3)grafted with different percent yield


Surface peroxide concentration determination

Relationship between the peroxide concentration in the PET film and the ozonization time

Figure 2 shows the concentration of the peroxides that evolved on the PET surface treated by ozone. The concentration increased quickly with increasing ozonization time during the first 60 min. However, the peroxide concentration increased slowly after 60 min of exposure to the ozone gas. Perhaps the concentration neared saturation on the PET surface. Therefore, 60 min was set as the ozonization time.


Results and Discussion

Theory of grafting

Surface peroxide concentration determination

ROOH+Fe2+ RO?+OH-+Fe3+

2RO?+2H++3I- 2ROH+I3-

2 Fe3++3I- 2 Fe2++I3-

ROOH+2H-+3I- ROH+H2O+ I3-

Dosage of Ferrisulphas or PAAc polymer grafted onto the PET surface

can deoxidize POOH to OH- which can t initiate radical polymerization, as a result, the generation of homopolymer is prevented. At the same time, can also dioxide PO? that initiate grafting polymerization, but (k2 ?k1). As a result, the homopolymerization was restrained. In the experiment, when observed maximum graft rate, the concentration range of Fe2+ can be determined as (unknown).

Peroxides generated by ozonization were reduced into radicals to initiate the grafting of AAc onto the PET film surface. However, it was inevitable that POOH decompose by heat to produce PO? and OH?. PO? induced copolymerization, whereas OH? induced homopolymerization. In the reaction, Fe2+ ion acted as follows:

Here POOH represents the polymeric peroxide. PO? was also reduced by Fe2+ (k2 ?k1). As a result, the homopolymerization was restrained.

[O Neill, T. J Polym Sci Polym Chem Ed 1972, 10, 569]

Influence of Ozonation Time

(1)weight loss rate The weight loss rate of PET films were increased with the prolonging of time.

(2) Surface peroxide concentration

Contact Angle Results


Grafting degree decreases with the reaction temperature, which is due to the introduction of peroxide in the membrane surface after ozone treatment, when adding Mohr salt, the system becomes a redox initiator one, this system with lower activation energy and fast polymerization rate can initiate polymerization at lower temperature. Temperature accelerates the decomposition of peroxide, but the life of free radicals decrease, as a result, the polymerization process is inhibited, the graft yield decreased.

Influence of Monomer Concentration

Influence of polymerization process

Influence of polymerization temperature


Liquid(water) Contact Angle versus different ozonization time plus Acrylic acid grafted. T=400C polymerization time=3h

Liquid(water) Contact Angle versus grafting time. ozonization time=30min T=400C

Relationship between the peroxide concentration in the PET nanofiber films and the ozonization time

Contact angle data as follows:


Run-No CA(M) IFT Err Vol

1 119.55783 0 14.96005 8.34829

2 104.42017 0 10.15126 9.21955

3 94.28380 0 6.55262 8.39898

2010*4*24* 30min 200ma

Run-No CA(M) IFT Err Vol

1 141.05400 0 11.28149 10.28833

2 137.60132 0 7.31457 9.13778

3 129.03580 0 10.86806 9.91828

2010*4*24* **2* 30min 200ma ***

Run-No CA(M) IFT Err Vol

1 134.71315 0 13.39065 9.98020

2 134.84042 0 7.96438 8.71263

3 113.69437 0 14.52993 10.33980

2010*4*17* ** 20min 100ma ***

Run-No CA(M) IFT Err Vol

1 78.96616 0 7.85455 6.36848

2 135.40126 0 5.59616 9.30480

3 91.52864 0 8.54627 10.22857

4 16.87206 0 128.45227 2.13473

2010*4*17* **2* 30min 100ma ***


Run-No CA(M) IFT Err Vol

1 21.47201 19.63330 679.94006 0.35852

2 61.96204 0 8.58644 7.28418

3 43.10248 0 625.91687 5.10647

4 49.71889 0 181.71478 6.18013

2010*4*17* ** 30min 100ma ***

The peroxide groups formed on the surface of PTFE film were utilized as the initiating points for further free radical grafting polymerization. Fig. 1 schemes this approach of PTFE surface modification.

Surface-initiating polymerization on the untreated PET films were examined with using AAc as a monomer. However, no AAc polymer chains were observed with the obtained sample to verify that the untreated PET films surface did not possess peroxides or free radicals to initiate the AAc polymerization. On the other hand, vinyl monomers including AAc, AAm and GMA were successfully polymerized onto the surfaces of O3 treated PTFE films.

The performance of grafting polymerization was first characterized FTIR-ATR and the spectra are shown in Fig. The pristine and modified PTFE films showed very different spectra in FTIRATR analysis to imply the occurrence of modification.

Further characterization on the modified PTFE films was conducted with XPS analysis and the spectra obtained were shown in Fig.

The above results directly demonstrated the success of utilization of ozone treatment for PTFE surface modification via surface initiated grafting polymerization.

One major targets of PET modification is to bring high hydrophilicity to its surface so as to enhance its adhesion property to other materials.

The surface hydrophilicity of the modified PET films were examined with water contact angle. The results are collected in Table. The hydrophobic surface of pristine PET films exhibited a large water contact angle of . After bringing PAAc onto PET surface the water contact angle dropped to.

This small water contact angle of PET-g-PAAc film surface demonstrated its high surface hydrophilicity, which was contributed from the polarity of the grafted COOH groups. Moreover, formation of hydrogen bonds between the carboxyl groups and water molecules also contributed to the extremely high surface hydrophilicity of

PET-g-PAAc film.


AAc, a hydrophilic vinyl monomer, was grafted onto an PET film surface by ozone-induced polymerization, and this was confirmed by XPS and ATR CFTIR. The surface hydrophilicity of the grafted film was greatly improved.