An environmental polyurethane retanning agent with the function of reducing free formaldehyde in leather

Accepted Manuscript An environmental polyurethane retanning agent with the function of reducing free formaldehyde in leather Xuechuan Wang, Zhuan Yan, Xinhua Liu, Taotao Qiang, Liang Chen, Peiying Guo, Ouyang Yue PII:

S0959-6526(18)33070-1

DOI:

10.1016/j.jclepro.2018.10.056

Reference:

JCLP 14458

To appear in:

Journal of Cleaner Production

Received Date: 4 May 2018 Revised Date:

11 September 2018

Accepted Date: 6 October 2018

Please cite this article as: Wang X, Yan Z, Liu X, Qiang T, Chen L, Guo P, Yue O, An environmental polyurethane retanning agent with the function of reducing free formaldehyde in leather, Journal of Cleaner Production (2018), doi: https://doi.org/10.1016/j.jclepro.2018.10.056. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

An environmental polyurethane retanning agent with the function of reducing free formaldehyde in leather Xuechuan Wanga* , Zhuan Yana, Xinhua Liua*, Taotao Qianga, Liang Chena, Peiying Guob, Ouyang Yuea a

RI PT

College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi’an 710021, Shaanxi, China; National Demonstration Center for Experimental Light Chemistry Engineering Education ( Shaanxi University of Science & Technology ) , Xi’an 710021, China.

b

*

Corresponding author. Tel: +86 -029-86132530;

SC

College of Arts and Sciences, Shaanxi University of Science and Technology, Xi’an, Shaanxi, People’s Republic of China 710021.

M AN U

E-mail address: [email protected](X Wang); [email protected](X Liu).

Abstract

Chromotropic Acid Grafted Amphoteric Polyurethane (CAGAPU) was synthesised with Chromotropic Acid (CA) as a modifier for Polyurethane (PU). The structure of CAGAPU was confirmed by FT-IR, 1H-NMR. The retanning process and

TE D

the experiments of CAGAPU with formaldehyde indicate the following: (1) The leather retanned by CAGAPU can be comparable or surpassed to the market PUbased retanning system in terms of shrinkage temperature and sensory performance.

EP

(2) The leather collagen fibers are smoother and orderly which provides a potential value for the appearance of the leather and fur industry. (3) The CAGAPU retanned system can bring down the free formaldehyde content in aldehyde tanned leather

AC C

significantly. (4) The optimum dosage of CAGAPU is 20 g and the best retanning time is 6 hours. (5) The CAGAPU retanned system can reduce the free formaldehyde, Biochemical Oxygen Demand (BOD), Total Dissolved Solids (TDS) and Total Suspended Solid (TSS) from the source which retard pound on the economy and environment greatly compare to the traditional governance. Therefore, this paper provides the possibility for the sustainable development of leather. The work has changed the traditional way of “terminal treatment” and realized the “initial treatment” and may also offer a new idea of solving the problem of formaldehyde in the newly decorated houses or in the air.

ACCEPTED MANUSCRIPT Keywords: amphoteric polyurethane, chromotropic acid, leather, retanning, reducing free formaldehyde

RI PT

1. Introduction China is known as a country of leather manufacturing with an annual output value of 1 trillion and 350 billion(Jiang N, 2006). With excellent performance, chrome tanning used to be taken as the primary method in the traditional tannery process. However, with the increasing awareness of environmental protection, people

SC

come to realize that the traditional chrome tanning method can bring pollution(Qiang T T et al., 2016; Ogata K et al., 2015). Therefore, researchers at home and abroad are

M AN U

considering using aldehyde tanning agents(Krishnamoorthy G et al., 2012; Lai S Q et al., 2017). But the problem is that aldehyde tanning agents will bring relatively high content of free formaldehyde which can induce carcinoma and promote cancer process, and free formaldehyde is not released only from tanning agents but also many other chemicals such as naphthalene based products, resins etc(G, Gurbuz et.al, 2008). There are strict regulations on the content of free formaldehyde in leather

TE D

products in different countries(QB/T 2955-2008, as shown in Table 1). Thus, it is of great necessity to explore methods to reduce free formaldehyde in the aldehyde tanned leather.

EP

Currently, the extensively used formaldehyde capture agents for reducing free formaldehyde in leather are ammonia or amino derivatives, strong oxidizing substances, porous inorganic filler and tannin, starch, casein(Mohammad Tasooji et

AC C

al., 2017; Wang X C et al., 2016). Rita Kakkar studied the absorption of free formaldehyde on Nano Magnesium Oxide and found that Nano Magnesium Oxide had a certain absorption effect on free formaldehyde(Kakkar R et al., 2004). Lam realized decreasing formaldehyde via oxidation under visible light by doping Cr on thin film based on TiO2(Lam R C et al., 2007). However, the above research methods have the disadvantages of high cost, complicated operation process and low removal rate of free formaldehyde, so they are not applicable in leather factories. Zhou YX found that the combination of polymer with small monomer which can react with free formaldehyde can increase the removal rate of free formaldehyde(Zhou Y X et al., 2006) . So if we can find a small monomer that can react with formaldehyde and then

ACCEPTED MANUSCRIPT use the small monomer to modify a large polymer, then the modified polymer will be a combination of small molecules and large polymer, and the removal rate of free formaldehyde will increase. Young-Sihn Sihn, Bo-Long Poh, E. Fagnani found that the chromotropic acid can react with formaldehyde so the chromotropic acid can be used as the small monomers(Young-Sihn Sihn et al., 1997; Bo-Long Poh et al., 1989;

RI PT

E Fagnani et al., 2003). That is to say, if we want to achieve the idea of combining small monomer and polymer to improve the removal rate of free formaldehyde, the key now is to choose a polymer. But which material could serve as the polymer?

At present, the amphoteric polyurethane retanning agent is widely used in leather

SC

retanning process because it can effectively solve the problem of loose grain and make leather plump, flexible, and elastic. It can also increase the binding rate of subsequent anionic materials(Wei shilin, 2010; He X W et al., 2017; Chen, W. Y et al.,

M AN U

2011). Different modifiers can give special properties and functions to polyurethane, such as amphoteric polyurethane with function of postpolymerization crosslinking, amphoteric polyurethane with self assembly properties and amphoteric polyurethane with temperature sensitive properties(Ren Z Y et al., 2015; Qiao Y et al., 2008; Dong A J et al., 2013). Therefore, it is assumed that amphoteric polyurethane (APU) will

TE D

have the function of reducing free formaldehyde when polyurethane is used as polymer and the chromotropic acid was introduced onto the main chain of the polyurethane as the small monomers. When such APU is applied in the retanning process of the aldehyde tanned leather, leather can be retanned with low content of

EP

free formaldehyde.

In our work, Chromotropic Acid Grafted Amphoteric Polyurethane (CAGAPU)

AC C

was synthesised with Chromotropic Acid (CA) as a modifier for Polyurethane (PU). The CAGAPU was then used in the retanning process of aldehyde tanned leather, which not only can avoid the problem of Cr (Ⅵ) pollution brought from traditional chrome tanning agent, but also can effectively reduce the free formaldehyde plagued by market aldehyde tanned system. What’s more, the BOD, TDS, TSS have been reduced to a certain extent in the waste liquid of tannery. This paper may provide the possibility for the sustainable development of aldehyde tanned leather. Table 2 shows the contributions and deficiencies of references closely related to this work(He, XW et al., 2017; Krishnamoorthy, G et al., 2012; Zhou, YX et al., 2012; Wang, YP et al., 2011). If using traditional formaldehyde catcher or wastewater treatment agent to treat free formaldehyde or BOD, TDS, TSS in the last special

ACCEPTED MANUSCRIPT section( Zhou YX et al., 2006; Mella, B et al., 2018; Janus, M et al., 2017), it would not only cause cumbersome operations in tanning industry but also some of free formaldehyde or BOD, TDS, TSS have been released during processing, which will have immeasurable lash on the environment(Taotao, Q et al., 2018). The CAGAPU prepared in this study can reduce the free formaldehyde in leather and BOD, TDS,

RI PT

TSS in the tannery wastewater in the indispensible retanning section of leather which could avoid the tedious defects of the traditional operations and prevent the pollution released by formaldehyde or BOD, TDS, TSS in the process of treatment. Therefore, this experiment has changed the traditional way of “terminal treatment” and realized

SC

the “initial treatment”. Last but not least, the work may also offer a new idea for solving the problem of formaldehyde in the newly decorated houses or in the air.

M AN U

Table 1

TE D

Table 2

2. Materials and methods

EP

2.1 Materials and equipment

Pickled sheepskin was supplied by Hebei Dongming leather Co., Ltd.

AC C

Isophorone Diisocyanate (IPDI, AR) was provided by Shanghai Dibo Chemical Technology Co., Ltd. Poly (Propylene Glycol 400) (PPG 400, ≥ 99.0%) and NMethyldiethanolamine (MDEA, ≥ 99.0%) were purchased from Aladdin Industrial Corporation. Chromotropic Acid (CA, AR) was obtained from Shanghai Macklin Biochemical Co., Ltd. Triethylamine (TEA, ≥ 98.0%) was produced by Guangdong Chemical Reagent Engineering-technological Research and Development Center. Sodium bicarbonate (Na2CO3, ≥ 98.0%) was supplied by Tianjin Hongyan Chemical Reagent Factory. Dibutyltin dilaurate (DBTDL, ≥ 98.0%) was purchased from Chengdu Kelong Chemical Reagent Co., Ltd.

ACCEPTED MANUSCRIPT The Fourier Transform-Infrared Spectroscopy (Vertex-70), X-ray diffraction (Advance- D8) and Nuclear magnetic resonance spectrometer ADVANCE (400MHz) were provided by German Brook company; Thermogravimetric analyzer (Q500) was supplied by American TA Company.

RI PT

2.2 Methods 2.2.1 Preparation of PU

100 mmol IPDI, 40 mmol PPG, 10mmol DMBA and 10 mmol MDEA were added into a three-necked flask and the temperature was controlled at 70Ⅵ for 4 h,

SC

using moderate DBTDL as the catalyst. Then a weight of 20 mmol TEA was added to the flask and the temperature was kept at about 40Ⅵ for 30 min. Finally, PU was obtained by adding a moderate amount of distilled water and the unreacted solvent

2.2.2 Preparation of CAGAPU

M AN U

was removed by rotary evaporator instrument.

CAGAPU was synthesized by PU with CA as a modifier. 5g CA was dissolved with a small amount of acetone in a beaker. Then, the dissolved CA was poured into the 100ml PU solutions and the temperature was raised to 80Ⅵ. The solution was

TE D

stirred quickly for 3 h. Then, 20 mmol of TEA, a proper amount of distilled water were added to the three-necked flask and with the addition of sodium bicarbonate to adjust the pH to 5.0. Then CAGAPU, an ivory liquid with blue light, was obtained by

EP

removing the unreacted monomers and solvent through dialysis bag. 2.2.3 Fourier transform-infrared spectroscopy (FT-IR)

AC C

Before characterization, the unreacted monomers and solvent were removed by

dialysis bag. Then the samples of CA, PU and CAGAPU were carried out using compressed pellets of KBr and the wave number ranged from 400 to 4000 cm-1. 2.2.4 Nuclear magnetic resonance spectrum (1HNMR) Before testing, the unreacted monomers and solvents were removed. Then the solid samples of CA, PU and CAGAPU were confected into a solution whose mass concentration was about 10% with DMSO-d6 as the solvent and then the samples was scanned 32 times. 2.2.5 Processing of leather

ACCEPTED MANUSCRIPT The sheepskins soaked with acid was tanned by market aldehyde tanned system and then divided into three groups whose starting states were roughly identical. Then the leather was retanned by multifarious retanned systems including PU retanned system, CAGAPU ratanned system and the market retanned system, and the other operation conditions were the same(Dan W H et al., 2006; Wei S L et al., 1999). The

Fig. 1

M AN U

2.2.6 Analysis of leather properties

SC

process was shown in Fig.1.

RI PT

detailed flow chart was shown in the Supporting Information. The whole experiment

2.2.6.1. Measurement of shrinkage temperature (Ts). The leather was hung on the hook of the test rack of the systolic temperature meter, the rack was then dropped into an electric cup equipped with water. While the spring in the device was stretched with the contraction of the leather, the systolic temperature meter would record the

2000).

TE D

temperature simultaneously, which is the shrinkage temperature of the leather(IUP 2,

2.2.6.2. Determination of physical properties. Horizontal and vertical samples from different parts of the leather were fixed on the XL-100A tensile testing machine. The tensile strength and tearing strength were tested and the average value was calculated.

EP

2.2.6.3. SEM observation. The leathers were observed under magnification of 5000 using the "scanning electron microscope (SEM) + energy spectrometer" of TESCAN.

AC C

2.2.6.4. Evaluation of sensory performance. According to the ISO 17235-2002, (ISO 17235-2002, 2002) the softness, fullness, compactness and smoothness of the leather were graded with a total score of 10 points and the lowest was 1 point. The average value was used as the final score of the comprehensive sensory evaluation. The higher the score, the better the sensory performance(Qiang T T et al., 2016). 2.2.6.5. Estimation of free formaldehyde content in the leather. (1) Sample treatment. In the light of standard appendix QB/T 19941-2005, steam distillation rather than direct distillation was used for determining the content of formaldehyde in leather(QB/T 19941-2005,2005; Xiaopeng Sun et al., 2006). Firstly, the leather samples were mashed and placed in the round bottomed flask. Then a

ACCEPTED MANUSCRIPT proper amount of distilled water and a small amount of phosphoric acid were added in the flask. When the above steps were completed, the distillation operation was carried out. (2) Drawing standard curves. The formaldehyde standard solutions with different concentration gradients were prepared. After being coloured with

RI PT

acetylacetone and ammonium salt, the standard curves were drawn at the maximum absorption wavelength of formaldehyde.

(3) Testing sample. A proper amount of sample solution was taken to determine the absorbance. Then the formaldehyde concentration of the sample was detected

SC

from the standard curves. The formula for calculating the removal rate of free formaldehyde of CAGAPU is: W=(X1-X2)/X1×100%

M AN U

Where W is the Removal rate of free formaldehyde (%) ; X1 is the free formaldehyde content of aldehyde tanned leather before retanning (mg/kg); X2 is the free formaldehyde content of aldehyde tanned leather after retanning (mg/kg). The flowsheet for estimation of free formaldehyde was shown in Fig.2.

TE D

Fig. 2

2.2.7. Experiment on the reaction of CAGAPU with formaldehyde. 2.2.7.1. Analysis the reaction mechanism of CAGAPU with formaldehyde.

EP

According to the reaction equation between the CA and formaldehyde, the reaction mechanism of CAGAPU with formaldehyde was analyzed.

AC C

2.2.7.2. The effect of the dosage of CAGAPU and different retanning time on the removal rate of formaldehyde. The aldehyde tanned leather was retanned with diverse dosages of CAGAPU and different retanning time, and then the removal rate of formaldehyde is calculated by measuring the content of formaldehyde in the leather before and after retanning. 2.2.8. Environmental impact assessment. According to the standard procedure, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) of leather waste water from different tanned and retanned systems were determined and the Total Dissolved Solids (TDS) and Total Suspended Solid (TSS) were calculated.

3. Results and discussion

ACCEPTED MANUSCRIPT 3.1. FT-IR analysis Curve (a), (b) and (c) in Fig.3. show the FT-IR spectrum of CA monomer, CAGAPU and PU. The wide peak at 3124 cm-1 of curve (a) is the result of phenol hydroxyl association in the CA(Liu YQ, 2006). The peak at 672 cm-1 can be attributed to the out-of-plane bending vibration of C-H in the benzene ring. The above

RI PT

characteristic peaks indicated that the main functional groups in the modifier CA are phenolic hydroxyl groups and benzene rings. The absorption peak at 3345 cm-1 of curve (b) indicates the stretching vibration of N-H. The absorption peak at 1739 cm-1 and 1546 cm-1 corresponds to the amide C=O bond stretching in the peptide bond

SC

(amide Ι, amide Ⅵ, respectively) (Wang XC et al., 2015). These characteristic peaks indicate that the CAGAPU(curve (b)) contain –CO-NH- functional groups (Ma JZ et

M AN U

al., 2017). The peak at 672 cm-1 and 632 cm-1 can be attributed to the out-of-plane bending vibration of C-H in the benzene ring. Compared with the curve (c), the characteristic absorption peak of the benzene ring appears in the curve (b) and the wide peak of the hydroxyl group in the curve (a) disappears, revealing that the CA was successfully grafted onto the polyurethane.

3.2 1H-NMR analysis

TE D

Fig. 3

EP

The 1H-NMR spectrum of CA monomer, PU and CAGAPU were shown in Fig. 4. (A), (B), and (C), respectively. It is known from Fig.4. (A) that δ: 2.50 corresponds

AC C

to the proton peak of (a) position of active hydrogen in the phenol hydroxyl group in the CA, while δ: 6.95 and δ: 7.52 correspond to the peaks of (b) , (c) position of interphase hydrogen on the benzene ring. δ: 10.93 of (d) position is the result of active hydrogen in –SO3H in the CA. As shown in Fig. 4. (B) that δ: 6.04 corresponds to the absorption peaks of active hydrogen in -CONH- in the PU (Zhang H, 2005). From Fig.4. (C), it can be seen that δ: 7.68 shows the double peaks of hydrogen in the benzene ring, which is larger than the absorption peaks in Fig.4. (A) (δ: 6.95 and δ: 7.52). This is due to the induction effect of the benzene ring in CA and the isocyanate group in polyurethane(Liu Y Q, 2006). And we can see that the peak at 2.50 in Fig.4. (A) did not appear in Fig.4. (B) and Fig.4. (C), indicating that all hydroxyl groups in

ACCEPTED MANUSCRIPT CA were all involved in the reaction and turned into the –CO-NH-. It also confirmed that CA was grafted onto the main chain of polyurethane.

Fig. 4

RI PT

3.3 Analysis of leather properties

In the work, we compared the performances of the sheepskin garment leather tanned by market aldehyde tanned system and retanned by multifarious systems. As

SC

for why these systems are designed, the reason is that the experiment is mainly aimed at solving the problem of formaldehyde content in the leather caused by market aldehyde tanned system in the process of retanning. So the premise is market

3.3.1 Shrinkage temperature (Ts)

M AN U

aldehyde tanned system, then different retanning systems are designed for comparison.

The shrinkage temperature (Ts) of leather treated with different systems were measured which is shown in Table 3. It can be seen from Table 3 that the Ts by PU retanned system, CAGAPU retanned system and market retanned system were

TE D

increased compared with that by the the market aldehyde tanned system. The results indicate that PU, CAGAPU and market retanning agents all permeated into the interval of the leather collagen fibers and produced transmission-quality from the drum bath to the leather collagen fibers. Some of these retanning agents that enter the

EP

collagen fibers had been filled in the pores of the fibers in the form of physical action and others may be chemically crosslinked with the fibers which made the moisture

AC C

and heat stability of leather (Ts) improved eventually(Ma J Z et al., 2017; Zhang H, 2005). Although the shrinkage temperature of leather retanned by CAGAPU was slightly lower than that of the market retanned system. While, from the error analysis of data, we can see that the difference presents very small. The shrinkage temperature of leather retanned by CAGAPU also can reach above 79Ⅵ which could totally meet the basic requirement of retanning agents. From the later study, we can see that CAGAPU retanned system increase the new efficacies that the market retanned system doesn't have, including of improving the comprehensive sensory evaluation value (CSEV) of leather and reducing the content of free formaldehyde in leather. Therefore, the CAGAPU retanned system will have a broad market value.

ACCEPTED MANUSCRIPT

Table 3

RI PT

3.3.2 Physical properties The physical properties of leather disposed by various systems were shown in Fig.5. As Fig.5. shows, the tensile strength and tearing strength by the CAGAPU retanned system was higher than that by the PU system. The mechanical strength CAGAPU retanned system was lower than that of market retanned system, but what

SC

deserves our attention is that the difference is not obvious. This was due to the large number of amide bonds in the CAGAPU can formed more hydrogen crosslinking with

M AN U

carboxyl group, amino group and hydroxyl group of leather collagen (Hannah C et al., 2013). Due to the crosslinking between retanning agents and leather collagen fibers, the deformation of fibers can be effectively suppressed(Qiang T T et al., 2016;.Ma J Z et al., 2014). In addition, the cation in CAGAPU can form electrovalence bond with the carboxyl group in the leather collagen fibers (as shown in Fig 6.) Therefore, the

TE D

tensile strength and tearing strength by the CAGAPU retanned system was good.

Fig. 5

EP

Fig. 6

AC C

3.3.3 SEM observation

Fig.7. represent the SEM images of the leather handled by different systems. As

is shown in Fig. 7(e), the leather collagen fibers retanned by CAGAPU system are more straight, compliant, and orderly compared to those retanned by other retanning systems. That is, the orientation of the fibers is more consistent which is probably due to the fact that the degree of crystallization of CAGAPU became larger so that the structure is more regular, which can be confirmed from the XRD diagram of CAGAPU in the Supporting Information. In addition, the collagen fibers of the leather after CAGAPU retanning system are more orderly, likely leading to the more regularity of the appearance of leather products retanned by CAGPU system. As a

ACCEPTED MANUSCRIPT result, it provides a vital potential value for leather and fur industry. Due to the smooth and regular appearance of the leather and fur is an important standard for evaluating the quality of its products.

RI PT

Fig. 7

3.3.4 Sensory performance . The

sensory performance of leather pretreated by various systems was counted in

SC

Table 4. Obviously, the fullness and the grain tightness of the acid skin were very poor. This resulting from the structure of the acid skin was destroyed by the materials in the preprocessing stage, so the leather fiber of acid hide was loose and hollow

M AN U

which were consistented with Fig. 7(a) of the SEM in the manuscript. However, in the market aldehyde tanned system, the fullness and the grain compactness of the leather were improved which was attributed to the crosslinking of multiple hydrogen bonds in araldehyde molecules and collagen fibers. Thus, the leather collagen fibers will be stitched again so that the fullness and the comprehensive sensory evaluation value (CSEV) will be improved. The CSEV of CAGAPU retanned system increased by a

TE D

grade compared with that of the PU retanned system and market retanned system. That was because CA was used as a modifier and also as a chain extender, which made the main chain of the PU molecules longer. What’s more, the leather collagen

EP

fibers were fully dispersed and become orderly rather than messy which was consistent with the Fig. 7(d). Consequently, the sensory performance of leather was

AC C

improved.

Table 4

3.3.5 Free formaldehyde content in the leather (1) Drawing standard curve A series of concentration gradient formaldehyde at the maximum absorption wavelength after coloration was determined and the standard curves were fit (as shown in the Supporting Information). The linear equation was Y=0.0047X-0.00357, R2=0.99877, which showed that the method has a good linear relationship.

ACCEPTED MANUSCRIPT (2) Calculation the content of free formaldehyde

Table 5

RI PT

Table 5 reflected the free formaldehyde content of leather treated by different systems. It was known from Table 5 that the free formaldehyde content in the leather retanned by CAGAPU retanned system was reduced to 56.08mg/kg, which conforms to EU countries' standards on leather products directly contact by humanbeings (75mg/kg). What is more, the value reduced greatly compared with that of the market

SC

aldehyde tanned system which indicates that the CAGAPU retanning agent can effectively reduce the free formaldehyde in aldehyde tanned leather and the removal

M AN U

rate of free formaldehyde has reached 80.95%. The reason is that the CA monomer can react with free formaldehyde and endow the performance of CAGAPU whose modifier is a CA monomer with reducing the content of free formaldehyde(Jennifer et al., 2005; Mohammad et al., 2017). While, the PU retanned system and market retanned system did not have the function of reducing free formaldehyde in leather. The reason is that there is no monomer which can react with the free formaldehyde in

TE D

the molecular structure of the PU and the market retanning agents. Therefore, the CAGAPU not only has the retanning function of market retanning agent, but also increase the new efficacy of improving the comprehensive sensory

leather.

EP

evaluation value (CSEV) of leather and reducing the content of free formaldehyde in

AC C

3.4 The reaction between CAGAPU and formaldehyde 3.4.1The reaction mechanism analysis of CAGAPU with formaldehyde Scheme 1 shows the reaction mechanism of CA with formaldehyde(Young-Sihn

Sihn et al., 1997; Bo-Long Poh et al., 1989; E. Fagnani et al., 2003). It can be seen that the reaction between CA and formaldehyde occurs between two naphthalene rings, and the hydroxyl group in the CA does not participate in the reaction. Therefore, the CAGAPU produced by the reaction of hydroxyl group in the CA with isocyanate group in the PU can still react with formaldehyde. So, when the CAGAPU is used as leather retanning agent, it can effectively reduce the free formaldehyde content in

ACCEPTED MANUSCRIPT leather. The reaction mechanism of CAGAPU with formaldehyde was drawn in the Scheme 2. Scheme 1

RI PT

Scheme 2

3.4.2. The effect of the dosage of CAGAPU and retanning time on the removal rate of formaldehyde

SC

The influence of CAGAPU’s dosage and retanning time on the removal rate of formaldehyde was shown in the Fig.8. It can be seen from the Fig.8 that with the

M AN U

extension of CAGAPU’s dosage and retanning time, formaldehyde-removal rate increased first and then remained unchanged. This is probably caused by the reaction between CAGAPU with formaldehyde in the leather which reached saturation point with 20g CAGAPU after 6 hours. For cost savings and efficiency consideration, the optimum dosage of CAGAPU is 20g and the best retanning time is 6 hours.

TE D

Fig. 8

3.5. Environmental impact assessment

EP

The leather industry has turned the stinking skin into a variety of leather products that people are satisfied with, however, there will be wastewater and sludge

AC C

in the process of tanning of leather. The environmental impact assessment is of great significance to the estimate of whether the tannery process is a sustainable development or not. At present, the main goal of cleaner production in leather industry is to reduce environmental pollution caused by wastewater and sludge. The most important parameters to evaluate the environmental impact of wastewater and sludge include Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Dissolved Solids (TDS) and Total Suspended Solid (TSS). The environmental parameters after multifarious systems were shown in Table 6. The COD of CAGAPU retanned system was higher than that of the PU retanned system and the market retanned system which may be due to the chain extender of CAGAPU

ACCEPTED MANUSCRIPT including anionic chain extender (CA) and cationic chain extender (MDEA) making the molecular weight of CAGAPU larger(Krishnamoorthy G et al., 2012; Roberto R et al., 2017). However, it is worth noting that the BOD, TDS, TSS of the CAGAPU retanned system have declined by 31.82%, 9.90% and 30.80% compared with those after the market retanned system. Combined with the process of determining the

RI PT

content of free formaldehyde above, that is to say, the CAGAPU synthesized in our laboratory can effectively reduce free formaldehyde, BOD, TDS and TSS. It showed that the CAGAPU retanned system has a sustainable future and may be of great significance to the cleaner production of the tannery industry(Md Abdul Moktadir et

3.6. Cost and novelty analysis 3.6.1. Novelty of synthetic methods

M AN U

Table 6

SC

al., 2018).

The synthesis idea and method of CAGAPU have never been proposed by other scholars. In order to solve the problem of free formaldehyde in leather industry, the

TE D

raw materials of polyurethane were searched by the method of back-stepping, so the CAGAPU with function of reducing free formaldehyde was successfully prepared. The CAGAPU is a new self-synthesized material with low price, wide source and

Table 7

AC C

EP

innocuity which can be confirmed from Table 7.

3.6.2. Novelty of retanning agent effect The scenarios before CAGAPU implementation correspond to the market tanned

system, and the scenarios after CAGAPU implementation in accordance with CAGAPU retanned system. It can be seen in Table 4, the sensory performance of leather after CAGAPU implementation can improved significantly compared with that before CAGAPU implementation. 3.6.3 Novelty of cleaner production in leather industry

ACCEPTED MANUSCRIPT According

to

the

National

Science

and

Technology

Major

Project

(2017YFB0308500), it is clear that ecological leather product engineering as the guidance, the development of environmental tanning, retanning, dyeing and finishing key materials as the breakthrough point, so as to achieve the clean and sustainable development of leather industry. Based on this, the work mainly focuses on the

RI PT

development of environmentally leather retanning materials, and targets to reduce leather pollution including free formaldehyde and BOD, TDS, TSS from roots and realize cleaner production and sustainable development of leather industry. 3.7 Sustainable improvement analysis

SC

Sustainable improvement is a global task, which encompasses every aspect of our daily lives. For us, the concept of clean and sustainable leather making has always

M AN U

been our pursuit, and we strive for it. Sustainable development is the development that meets the needs of the present without compromising the ability of future generations to meet their own needs. The sustainable improvement of this work is mainly reflected in the following three spheres. Ecological

sphere:

Ways

of

reducing

negative

human

impact

are

environmentally-friendly chemical engineering, environmental resources management

TE D

and environmental protection. This work reduced free formaldehyde, BOD, TDS, TSS from the source through self-synthesized environmentally CAGAPU retanning agent so as to achieve cleaner production and improve sustainability.

EP

Economic sphere: Leather products are an integral part of our lives, including clothing, bags, shoes and sofas, et, al. Retanning is one of the efficient ways to reuse

AC C

animal skin, and it can not only solve the environmental pollution caused by the effective ultilization of the animal's skin, but also greatly increase the additional value of animal hides, which is very meaningful to the environment and the economy. Social sphere: Human beings have more than 5000 years of leather culture, and

the leather products have been applied to all aspects of life by ancients, which is an important aspect of the rich ancient civilization. In contemporary culture, it also gives leather products the meaning of high-end and luxury. This experiment improves people's cognition and social sustainability for leather industry by providing a more comfortable, environmentally friendly ecological retanning route.

ACCEPTED MANUSCRIPT

4. Conclusions In conclusion, environmental polyurethane (CAGAPU) with function of reducing free formaldehyde in leather has been synthesized by using Chromotropic

RI PT

Acid (CA) and Polyurethane (PU) as raw materials. The structure of CAGAPU was confirmed by FT-IR, 1H-NMR. Further, through the comparison of multifarious systems, it was found that the CAGAPU not only has the retanning function of market retanning agent, but also increase the new efficacies of improving the comprehensive

SC

sensory evaluation value (CSEV) of leather and reducing the content of free formaldehyde in leather from the source. The CAGAPU retanned system can bring down the free formaldehyde content in aldehyde tanned leather to 56.08 µg/kg (the

M AN U

value is in conformity with the provisions of EU countries) and the removal rate of free formaldehyde has reached 80.95%. The CAGAPU retanned system can reduce the free formaldehyde and BOD, TDS, TSS from the source which retard pound on the economy and environment greatly compare to the traditional governance. Therefore, this experiment has changed the traditional way of “terminal treatment”

TE D

and realized the “initial treatment”. The work may be of great significance to the cleaner production of the tannery industry. Last but not least, the work may also provide a new idea of solving the problem of formaldehyde in the newly decorated houses or in the air.

EP

Supporting information

AC C

XRD Analysis and TGA Analysis of PU and CAGAPU, specific operation flow chart of the leather process, the standard curve of formaldehyde.

Acknowledgments

This study was supported by National Key R&D Program of China

(2017YFB0308500); National Natural Science Foundation of China (21476134) .

References Jiang, N., 2016. The chinese leather industry under the numbers. J. Chinese leather. 2, 74-79.

ACCEPTED MANUSCRIPT Qiang, T, T., Gao, X., Ren, J., Chen, X, K., Wang, X, C., 2016. A chrome-free and chrome-less tanning system based on the hyperbranched polymer. J. ACS Sustainable Chem. Eng. 3, 701-707. Ogata, K., Kumazawa, Y., Koyama, Y., Yoshimura, K., Takahashi, K., 2015. Measurement of hexavalent chromium in chrome-tanned leather: comparative

RI PT

study of acidic condition extraction with alkaline extraction. J. Soc. Leather Technol. Chem. 6, 293-296.

Krishnamoorthy, G., Sadulla, S., Sehgal, P, K., Asit, B, M., 2012. Green chemistry approaches to leather tanning process for making chrome-free leather by

SC

unnatural amino acids. J. Journal of Hazardous Materials. 215, 173-182.

Lai, S. Q., Jin, Y., Li, H, P., Zhang, L., Jin, X., 2017. Application of Y-shaped polyurethane and polyacrylic acid as a complex retanning agent in aldehyde-

M AN U

tanned goat leather. J. Am. Leather Chem. Assoc. 11, 367-376.

G, Gurbuz., E, Kilic., E, Bayramoglu., A, Korgan., D, Kalender., 2008. Elimination of free formaldehyde in leather by using vinca rosea and camellia sinensis extracts. J. Am. Leather Chem. Assoc. 3, 119-122.

QB/T 2955-2008., 2008. People's Republic of China light industry standard.

TE D

Mohammad, Tasooji., Guigui, Wan., George, Lewis., Heather, Wise., Charles, E, Frazier., 2017. Biogenic Formaldehyde: Content and Heat Generation in the Wood of Three Tree Species. J. ACS Sustainable Chem. Eng. 5, 4243-4248. Wang, X, C., Zhang, T., Ren, L, F., 2016. A active methylene hyperbranched

EP

formaldehyde catcher and its preparation method. P. 201610149881.2. Kakkar, R., Kapoor, N, P., Klabunde, J, K., 2004. Theoretical study of the adsorption

AC C

of formaldehyde on magnesium oxide nanosurface: size effects and the role of low coordinated and defect sites. J. Phys Chem B. 108, 18140 -18148.

Lam, R, C, W., Leung, M, K, H., Leung, D, Y, C., 2007. Visible -light assisted photocatalytic degradation of gaseous formaldehyde by paralled -plate reactor coated with Cr ion-implanted TiO2 thin film. J. Sol. Energy Mater. Sol.Cells. 1,

54-61. Zhou, Y, X., Chen, F, X., Chen, J., 2006. Synthesis free formaldehyde catcher with amino. J. China leather. 11, 27-33. Young-Sihn, Sihn., J, K, Guillory., Lee, E, Kirsch., 1997. Quantitation of taurolidine decomposition in polymer solutions by chromotropic acid formaldehyde assay method. J. Journal of pharmaceutical and biomedical analysis. 4, 643-650.

ACCEPTED MANUSCRIPT Bo-Long, Poh., Chooi, Seng, Lim., Kong, Soo, Khoo., 1989. A water-soluble cyclic tetramer form reacting chromotropic acid with formaldehyde. J. Tetraahedron letters. 8, 1005-1008. E. Fagnani., C, B, Melios., L, Pezza., H, R,

Pezza., 2003. Chromotropic acid-

formaldehyde reaction in strongly acidic media. The role of dissolved oxygen

RI PT

and replacement of concentrated sulphuric acid. J. Talanta. 1, 171-176. Wei, shilin.,2010. Modern chinese-english dictionary of leather and fur industry; Chinese Light Industry Press: Beijing.

He, X, W., Zhou, J, F., Wang, Y, N., 2017. Application method and principle

SC

exploration of amphoteric polyurethane retanning agent. J. Leather science and Engineering. 1, 5-12.

Chen, W, Y., Li, G, Y., 2011. Tanning Chemistry; Chinese Light Industry Press:

M AN U

Beijing.

He, X, W., Zhou, J, F., Wang, Y, N., Shi, B., 2017. Application method and action mechanism of an amphoteric polyurethane retanning agent. Leather science and engineering. 27, 5-12

Ren, Z, Y., Liu, L., Wang, H, F., Fu, Y., Jiang, L., Ren, B, X., 2015. Novel

TE D

amphoteric polyurethane dispersions with postpolymerization crosslinking function derived from hydroxylated tung oil: synthesis and properties. J. RSC advances. 35, 27717-27721.

Qiao, Y., Zhang, S, F., Lin, O., 2008. Stabilized micelles of amphoteric polyurethane

EP

formed by thermoresponsive micellization in HCl aqueous solution. J. Langmuir. 7, 3122-3126.

AC C

Dong, A, J., Hou, G, L., Sun, D, X., 2013. Properties of amphoteric polyurethane waterborne dispersions. II. Macromolecular self-assembly behavior. J. Journal of colloid and interface science. 2, 276-281.

Mella, B., Barcellos, BSD., Costa, DED., Gutterres, M., 2018. Treatment of Leather Dyeing

Wastewater

with

Associated

Process

of

Coagulation-

Flocculation/Adsorption/Ozonation. J. OZONE-SCIENCE & ENGINEERING. 40, 133-140. Janus, M., Mozia, S., Bering, S., Tarnowski, K., Mazur, J., Morawski, AW., 2017. Application of MBR technology for laundry wastewater treatment. J. DESALINATION AND WATER TREATMENT. 64, 213-217. Wang, YP., Cao, H., Liu, ZL., Sheng, MZ., 2011. Synthesis of Hyperbranched Poly

ACCEPTED MANUSCRIPT ( amido amine) as a formaldehyde eliminate reagent for leather products. J. China leather. 40, 1-4. Taotao, Q.; Liang, C.; Qi, Z.; Xinhua, L.; 2018. A sustainable and cleaner speedy tanning system based on condensed tannins catalyzed by laccase. J. Cleaner Prod. 197, 1117-1123.

RI PT

IUP 2, 2000. Sampling. J. Soc. Leather Technol. Chem. 84, 303−309. ISO 17235-2002, 2002. Leather-physical and mechanical tests-determination of softness; International Standardization Organization.

QB/T 19941-2005., 2005. Leather−Chemical tests-Deetmrination of formadehude in

SC

leather. The light industry standards of the People’s Republic of China.

Xiaopeng, Sun., Yong, Jin., Shuangquan, Lai., Jiezhou, Pan., Weining Du., Liangjie Shi., 2018. Desirable retanning system for aldehyde-tanned leather to reduce the

Cleaner Prod. 175, 199-206.

M AN U

formaldehyde content and improve the physical-mechanical properties. J.

Dan, W, H., Chen, F, X., 2006. Tannery chemistry and technology; Chinese Light Industry Press: Beijing.

Wei, S, L., Liu, Z, H., Wang, H, R., 1999. Tannery Technology; Chinese Light

TE D

Industry Press: Beijing.

Liu, Y, Q., 2006. Modern Instrumental Analysis; China Higher Education Press: Beijing.

Wang, X, C., Shang, Y, M., Ren, L, F., Zhang, S, F., Guo, P, Y., 2015. Preparation

EP

and surface sizing application of sizing agent based on collagen from leather waste. J. Bioresources. 4, 7220-7231.

AC C

Ma, J, Z., Gao, J, J., Wang, H, D., Lyu, B., Gao, D, G., 2017. Dissymmetry gemini sulfosuccinate surfactant from vegetable oil: a kind of environmentally friendly fatliquoring agent in the leather industry. J. ACS Sustainable Chem. Eng. 5,

10693-10701.

Zhang, H. Modern organic spectroscopic analysis; Chemical Industry Press: Beijing, 2005. Hannah, C., Wells, R, L., Edmonds, N, K., Adrian, H., Stephen T. M., Richard, G, H., 2013. Collagen fibril diameter and leather strength. J. Agric. Food Chem. 47, 11524–11531.

ACCEPTED MANUSCRIPT Ma, J, Z., Lv, X, J., Gao, D, G., Li, Y., Lv, B., Zhang, J., 2014. Nanocomposite-based green tanning process of suede leather to enhance chromium uptake. J. Cleaner Prod. 72, 120−126. Roberto, R., Martina, Pini., Massimo, C., Anna, M, F., 2017. Environmental sustainability assessment of a new degreasing formulation for the tanning cycle

RI PT

within leather manufacturing. J. Green Chemistry.19, 4571-4582. Md, Abdul, Moktadir., Towfique, Rahman., Md, Hafizur, Rahman., Syed, MithunAli., Sanjoy, Kumar Paul., 2018. Drivers to sustainable manufacturing practices and circular economy: A perspective of leather industries in Bangladesh. J. Cleaner

AC C

EP

TE D

M AN U

SC

Prod. 174, 1366-1380.

ACCEPTED MANUSCRIPT Figure and Scheme captions Graphical abstract Fig.1. The whole experimental process Fig.2. The flowsheet for estimation of free formaldehyde Fig.3. FT-IR spectrum of the CA(a) , CAGAPU(b) and PU(c)

RI PT

Fig.4. 1H-NMR of the CA(A), PU(B) and CAGAPU(C) Fig.5. The physical properties of leather Fig. 6. Retanned mechanism of CAGAPU

Fig.7. SEM of the acid leather(a) and (b), market aldehyde tanned system (c) , PU

retanned system (d) , CAGAPU retanned system (e) and market retanned system (f)

SC

Fig.8. The influence of CAGAPU’s dosage and retanning time on the removal rate of formaldehyde

M AN U

Scheme 1. Reaction mechanism of CA with formaldehyde

AC C

EP

TE D

Scheme 2. Reaction mechanism of CAGAPU with formaldehyde

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Table captions

Table 1. Regulations of free formaldehyde content in leather from different countries Table 2. Contributions and deficiencies of references closely related to this work Table 3. The shrinkage temperature of leather by multifarious systems (Ⅵ)

Table 5. Free formaldehyde content of different systems

RI PT

Table 4. Sensory performance of leather after various systems

Table 6. Environmental impact assessment after multifarious systems

AC C

EP

TE D

M AN U

SC

Table 7. Cost, toxicity and function of CA, PU and CAGAPU

ACCEPTED MANUSCRIPT free formaldehyde content (mg/kg)

Countries/ Standards

skin contact products

not contact by skin

≤20

≤75

≤200

≤20

≤75

≤300

cannot be detected

≤75

≤20

≤200

≤20

≤75

≤20

≤75

European Union Japan France OKO Tex GB20400-2006 Okeo-Tex Standard 100 SG Mark

≤50

ECO-Tex Standard 100

M AN U

≤75

RI PT

articles for babies

SC

China

Australia

AC C

EP

TE D

Germany

≤300 ≤400 ≤300 ≤300 ≤150 ≤300

≤100

≤1500

≤100

≤1500

ACCEPTED MANUSCRIPT Title

Contributions

Deficiencies

He, X, W.,

Application method and

A kind of amphoteric

ZPU retanning agent doesn't

Zhou, J, F.,

action mechanism of an

polyurethane retanning (ZPU)

have the function of

Wang, Y,

amphoteric

was prepared and the action

reducing free formaldehyde

N., et. al

polyurethane retanning

mechanism of polyurethane

and BOD, TDS and TSS.

agent.

retanning agent was studied.

Krishnamoo

Green chemistry

Unnatural d-amino acids (d-

rthy, G.,

approaches to leather

AA)-aldehyde (Ald) as a

Sadulla, S.,

tanning process for

substitute for chrome-free

Sehgal, P,

making chrome-free

tanning has been attempted and

formaldehyde after different

K., et. al

leather by unnatural

total solids content (TSC)

tanning systems.

amino acids.

decreased significantly.

Zhou, Y,

Synthesis free

A free formaldehyde capture

The free formaldehyde

X., Chen, F,

formaldehyde catcher

agent containing amino has

catcher was used for the

X., Chen, J

with amino.

been synthesized.

treatment of the free

Wang, YP.,

Synthesis of

Cao, H.,

Hyperbranched Poly

Liu, ZL., et.

( amido amine) as a

al

formaldehyde eliminate

AC C

EP

products.

In the Environmental impact assessments, the work didn't measure and evaluate free

SC

M AN U

Hyperbranched Poly ( amido amine) was synthesized and

applicated in free formaldehyde

TE D

reagent for leather

RI PT

Authors

of leather products.

formaldehyde in leather at the terminal special procedure which leads to the tedious process of tannery.

ACCEPTED MANUSCRIPT leather

along

across

average

2

3

4

acid hide

45.2

44.6

46.0

45.8

45.4±0.3

market tanned systema

71.5

73.4

70.6

71.9

71.8±1.0

PU retanned systemb

74.3

74.7

76.2

75.5

75.2±0.5

CAGAPU retanned systemc

79.5

79.1

78.6

79.2

79.1±0.1

market retanned systemd

79.3

78.6

80.5

79.0

79.4±0.5

a

RI PT

1

market aldehyde tanned system: a tanned system based on the market aldehyde tanning agent. PU retanned system: retanned system based on the bPU synthesized by our laboratory. c CAGAPU retanned system: retanned system based on the cCAGAPU retanning agent synthesized by our laboratory. d market retanned system: a retanned system based on a PU retanning agent sold in the United States.

AC C

EP

TE D

M AN U

SC

b

ACCEPTED MANUSCRIPT fullness

softness

compactness

smoothness

comprehensive

acid hide

3

4

2

3

3

market tanned system

5

6

4

5

5

PU retanned system

7

7

6

8

7

CAGAPU retanned system

8

9

8

7

8

market retanned system

8

7

7

RI PT

leather

AC C

EP

TE D

M AN U

SC

6

7

ACCEPTED MANUSCRIPT

absorbance

formaldehyde concentration

removal rate

market tanned system

1.38

294.38 (X1)

0 (starting standard)

PU retanned system

1.39

296.50

-0.72

CAGAPU retanned system

0.26

56.08 (X2)

80.95

market retanned system

1.37

290.25

AC C

EP

TE D

M AN U

SC

RI PT

leather

1.40

ACCEPTED MANUSCRIPT BOD (mg/L)

COD (mg/L)

TDS (mg/L)

TSS (mg/L)

acid hide

754±23

1256±35

56783±26

351±32

market tanned system

958±15

1421±42

59432±31

564±25

PU retanned system

273±18

562±30

6725±28

270±36

CAGAPU retanned system

165±19

678±37

5689±34

182±21

market retanned system

242±27

589±26

6314±31

AC C

EP

TE D

M AN U

SC

RI PT

leather

263±39

ACCEPTED MANUSCRIPT Function of retanning

Function of reducing free

Type

Cost

Toxicity

leather

formaldehyde in leather

CA

¥ 1/g

innocuity

Without this function

Have this function

PU

¥ 58/L

innocuity

Have this function

Without this function

CAGAPU

¥ 60/L

innocuity

Have this function

AC C

EP

TE D

M AN U

SC

RI PT

Have this function

ACCEPTED MANUSCRIPT 1. A new and sustainable retanned system has been proposed. 2. It was consisted of small molecule of chromotropic acid and polyurethane macromolecule. 3. It increases the new efficacies of improving the comprehensive sensory evaluation

RI PT

value (CSEV) of leather and reducing the content of free formaldehyde in leather. 4. It has changed the traditional way of “terminal treatment” and realized the “ initial

AC C

EP

TE D

M AN U

SC

treatment” of free formaldehyde in leather and BOD,TDS,TSS in tannery wastewater.