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    Home > Coatings News > Resin News > 【Literature Interpretation】This bio-based dimer acid-modified water-based polyurethane can significantly improve the waterproof, oil-proof and mechanical properties of paper products

    【Literature Interpretation】This bio-based dimer acid-modified water-based polyurethane can significantly improve the waterproof, oil-proof and mechanical properties of paper products

    • Last Update: 2022-04-19
    • Source: Internet
    • Author: User
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    Key words: paper dimer acid water-based polyurethane water-resistant oil-resistant


    Background introduction


    Paper products are regarded as one of the most promising materials to replace traditional disposable plastic products due to their light weight, biodegradability, green environmental protection and good mechanical properties
    .
    So far, paper products account for about 50% of packaging materials

    .
    However, due to the hydrophilic and porous structure of lignocellulose, water and oil penetrate into the inside of the paper through the pores between the fibers by means of capillary action, resulting in a decrease in the mechanical properties of the paper after wetting, which limits its large-scale packaging applications in
    coatings online.
    coatingol.
    com

    .
    In order to solve this problem, paper mills often use low surface energy fluorine-containing chemicals (such as fluoroacrylates, fluoroalkyl polymers, etc.
    ) to improve the water and oil resistance of paper

    .
    However, fluorine-containing chemicals will generate perfluorooctanoic acid (PFOA) during the preparation and use, which is harmful to humans and the environment

    .
    Therefore, the development of green environmental protection waterproof and oil-repellent coatings has become an urgent problem to be solved in the paper packaging industry

    .


    Water-based polyurethane (WPU) is a high molecular polymer formed by the polymerization of polyisocyanate and polyol.
    It has the advantages of green environmental protection, high bonding strength, good film-forming performance, and adjustable flexibility.
    It has been widely used in coatings and adhesives.
    , fabric coating finishing and other fields

    .
    The molecular structure of WPU contains a large number of polar groups such as carbamate, ester group and ether bond, which form a dense film on the surface of the paper through hydrogen bonding, which can effectively block the penetration of water and oil

    .
    However, WPU uses water as the dispersion medium, and hydrophilic groups are introduced into its molecules.
    The cross-linking density of the WPU film is low, and the water and oil repellency is insufficient

    .
    Therefore, WPU needs to be modified to meet the paper surface performance requirements

    .
    At present, the market mainly uses acrylate, epoxy resin, silicone and inorganic nanomaterials to modify water-based polyurethane, but the above modification methods are all derived from petrochemical resources

    .
    With the increasing attention to environmental issues and the depletion of petroleum raw materials, the use of renewable biomass resources to replace traditional non-renewable petrochemical resources has become the general trend

    .


    Cao Yunfeng's team from Jiangsu Key Laboratory of Pulp and Paper Science and Technology used flexible diethylene glycol and bio-based dimer acid as raw materials to synthesize dimer acid-based polyester polyol (DG), and prepared a series of dimer acid-based Waterborne polyurethanes (DWPUs) with good flexibility and high molecular weight
    .
    The structures of DG and DWPUs were systematically investigated by ATR-FTIR, ¹H NMR, ¹³C NMR and GPC

    .
    The effects of DG content on water resistance, oil resistance, mechanical properties and thermal stability of DWPUs coated paper were systematically studied

    .
    The prepared dimer acid-based waterborne polyurethane provides a new method for developing high-quality, multifunctional, and environmentally friendly papermaking coatings

    .
    The team's research results will be published in Materials & Design in December 2021

    .


    research content

    1.
    Preparation of dimer acid-based polyester polyol (DG)


    DG was synthesized by direct esterification of dimer acid (DA) and diethylene glycol at high temperature using dibutyltin dilaurate as a catalyst (Scheme 1)
    .
    110 g of dimer acid, 31 g of diethylene glycol, 33 g of xylene (30 wt % relative to dimer acid) and 0.
    055 g of dibutyltin dilaurate (0.
    05 % wt % relative to dimer acid) were added to the nitrogen inlet.
    in a four-neck round-bottomed flask

    .
    The reaction was carried out at 180 °C for 6 h under nitrogen protection while removing the water released during the esterification process

    .
    When the acid value of the system was lower than 1.
    5 mg KOH/g, the reaction was stopped and cooled to room temperature

    .
    After removal of excess solvent, the remaining product was named DG

    .
    The hydroxyl value of DG was 34.
    49 mg KOH/g, the acid value was 0.
    158 mg KOH/g, and the esterification rate was 99.
    84%

    .
    The weight average molecular weight (Mw) of DG was 14368 g/mol, the number average molecular weight (Mn) was 4927 g/mol, and the polydispersity index (PDI) was 2.
    91

    .

    2.
    Preparation of Dimeric Acid-Based Waterborne Polyurethanes (DWPUs)


    The synthesis of DWPUs adopts a two-step polymerization method
    .
    First, polycaprolactone polyol (PCL) and DG were dehydrated under vacuum at 115 °C for 2 h, and 10 g of polycaprolactone polyol (PCL) and 0.
    31 g of DG were taken into a four-neck round-bottomed flask equipped with an electromagnetic stirrer.
    in

    .
    3.
    57 g of TDI was added dropwise to the four-necked flask, and the reaction was carried out at 80 °C for 2 h

    .
    After that, 1.
    11 g DMPA was added to react at 80 °C for 2 h

    .
    Add 6-12 ml of acetone to the reaction at 45°C to reduce the viscosity of the system

    .
    The reaction mixture was then cooled to 30 °C, neutralized with 0.
    83 g of TEA for 0.
    5 h, and finally 64 g of deionized water was added, and dispersed and emulsified at high speed (300 rpm) for 30 min

    .
    DWPUs were obtained after removal of acetone with a rotary evaporator

    .

    3.
    Preparation of DWPUs film


    The resulting DWPUs were poured into Teflon molds and left at room temperature for 24 hours
    .
    Subsequently, the residual moisture in the DWPUs was removed by heating at 50 °C for 8 hours

    .
    DWPUs film thickness is about 0.
    5 ~ 0.
    7 mm

    .


    4.
    Preparation of DWPUs Coated Paper


    DWPUs were used for surface sizing of the base paper with a basis weight of 63 g/m2, and the surface sizing experiment of the base paper used the coating machine coating method
    .
    The sizing papers were placed in a constant temperature oven at 50 °C for 5 min, and all papers were pretreated at 25 °C and 50% relative humidity (RH) before further testing

    .


    Results discussion

    1.
    Preparation and characterization of dimer acid-based polyester polyol (DG)

    2.
    Preparation and properties of DWPUs

    3.
    Preparation and properties of DWPUs coated paper

    in conclusion


    By introducing dimer acid-based polyester polyols, new dimer acid-based water-based polyurethanes (DWPUs) were prepared with good flexibility and high molecular weight, and were used for the first time in the preparation of water- and oil-resistant paper products
    .
    The mechanism of water and oil resistance of DWPUs coatings can be attributed to the following aspects: (1) the non-polar long-chain alkyl groups of DG endow DWPUs films with excellent hydrophobicity; (2) a continuous and uniform DWPU-derived film is formed on the paper surface, reducing the It improves the porosity of the paper and helps to enhance the water and oil resistance of the DWPU coated paper

    .
    When the DG content reached 7 wt%, the DWPU coated paper exhibited the highest water and oil resistance (the Cobb 60 value decreased by 88.
    06%, and the oil resistance value increased by 8.
    7 times)

    .
    But with the increase of DG content, the water and oil resistance decreased slightly, which may be due to the decrease of the uniformity of DWPU coating film by DG

    .
    The mechanical properties of the paper coated with DWPUs were increased by 26.
    75%, 42.
    31% and 27.
    04%, respectively, compared with the tensile strength, folding strength and elongation at break of the uncoated DWPUs paper

    .
    The process can provide high-quality, multi-functional and environmentally friendly water- and oil-resistant coatings for paper products, which is of great significance to the application of paper packaging

    .


    References: LiD, Hu D, Tan J, et al.
    Design and synthesis of dimer acid-based waterbornepolyurethane as water- and oil-resistant coating for paper substrates[J].
    Materials & Design, 2021,211:110142.
    LiD, Hu D, Tan J, et al.
    Design and synthesis of dimer acid-based waterbornepolyurethane as water- and oil-resistant coating for paper substrates[J].
    Materials & Design, 2021,211:110142.


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