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Preparation and performance analysis of water absorbing materials made from urea formaldehyde and cellulose blended foam

Superabsorbent polymers (SAPs) are widely used in agriculture, environmental remediation and industrial spill treatment, but mainstream petroleum-based polyacrylate absorbents have obvious drawbacks: non-biodegradable, high raw material cost, severe salt tolerance decline in saline soil, causing long-term soil microplastic pollution.

Urea formaldehyde is a low-cost porous base material with lightweight, easy forming and partial water absorption capacity. However, pure UF foam suffers fatal defects: severe shrinkage & cracking after drying, high pulverization rate, poor mechanical toughness, short water retention cycle, limiting large-scale promotion as absorbents.

Hydroxypropyl methylcellulose (HPMC) is renewable biomass cellulose derivative with massive hydroxyl groups, which can crosslink with UF molecular chains to improve foam flexibility and basic water absorption. Still, single HPMC modified UFHM foam still shows pore collapse and surface cracks. To solve this bottleneck, KH550 silane-coupled hydrophilic nano silica (HSN) is introduced as secondary reinforcing filler to build triple crosslinked UF-HPMC-HSN (UHMS) composite foam absorbent.

This article systematically elaborates the whole physical foaming preparation route, single-factor & orthogonal optimization of raw material dosage, microscopic morphology (SEM/EDS), molecular structure (FTIR/Raman), crystal form (XRD) and thermal stability (TGA) characterization, as well as water absorption, water retention, cycle regeneration performance test data, providing scalable green absorbent production formulas for agricultural material factories and environmental engineering manufacturers.

raw Materials & Standard UHMS Foam Preparation Process

Core Experimental Raw Materials

  • Matrix: Water-soluble urea formaldehyde (UF) prepolymer
  • Biomass modifier: HPMC (hydroxypropyl methylcellulose)
  • Foaming system: SDS sodium lauryl sulfate (foaming agent), MPS silicone polyether emulsion (foam stabilizer)
  • Nano reinforcing filler: HSN hydrophilic nano SiO₂, KH550 silane coupling agent (surface pretreatment)
  • Curing agent: Phosphoric acid
  • Dispersant: Anhydrous ethanol + deionized water for nano silica ultrasonic dispersion

Four-Step UHMS Manufacturing Flow

  • HPMC aqueous solution preparation: Heat deionized water to 85°C, dissolve HPMC under low-speed stirring to form uniform viscous liquid
  • HSN pretreatment: Mix HSN powder with ethanol-water solvent, add KH550, ultrasonic disperse 1h under ice bath to eliminate nanoparticle agglomeration
  • Foam liquid compounding: Blend UF prepolymer, HPMC solution, pretreated HSN, SDS foaming agent, MPS stabilizer under high-speed stirring (3500 r/min optimal)
  • Acid curing & room temperature drying: Add phosphoric acid to adjust pH for crosslink curing, cast mold, dry at 25°C to obtain finished white porous UHMS foam

Stage 1: Single HPMC Modified UFHM Foam (Base Composite System)

Before adding nano silica, HPMC dosage screening determines the basic pore structure and mechanical properties of UF foam. Test gradient: 4.4%–8.0% HPMC mass fraction (based on UF resin).

Orthogonal Test Optimal Base Formula

Three key foaming components are screened via orthogonal experiment:
  • HPMC: 6.4%
  • SDS foaming agent: 8.0%
  • MPS foam stabilizer: 8.0%

Optimal stirring speed: 3500 r/min (balances foam uniformity and pore opening rate)

Defects of Single UFHM Foam

Even under optimal HPMC ratio, the base foam still has prominent problems:
  1. Visible shrinkage & cracks after air drying
  2. High pulverization rate (7.81%), easy powder shedding under friction
  3. Insufficient mechanical toughness, pore wall collapses after multiple water absorption cycles
  4. Limited water retention capacity (only 168h for deionized water)

These drawbacks require secondary nano silica reinforcement modification.

Comprehensive Performance of Optimized UHMS Absorbent (6% HSN, 6.4% HPMC)

Water Absorption & Salt Tolerance Capacity

  • Deionized water absorption: 17.28 g/g
  • Tap water absorption: 13.36 g
  • 0.9% NaCl saline absorption: 11.06 g/g
     
Absorption equilibrium reaches within 48h; fast initial liquid uptake via interconnected porous capillary channels.

Long-Term Water Retention Performance

  • Deionized water retention cycle: ≥216h (9 days)
  • Tap water retention: 192h
  • Saline solution retention: 168h

HPMC gel network + HSN nano hydrogen-bond dual system locks water molecules and slows evaporation loss.

Cyclic Regeneration Durability

After 10 repeated absorption-drying cycles:
  • 1st cycle benchmark: 100% absorption
  • 5th cycle retention rate: 86%
  • 10th cycle retention rate: 59%

Far superior to pure UFHM foam (only 52% after 10 cycles), nano silica framework prevents irreversible pore collapse.

Mechanical & Anti-Pulverization Properties

  • Compressive strength: 0.336 MPa (+37.7% vs single HPMC foam)
  • Pulverization rate: 3.62% (52.9% reduction from base UFHM foam)

Dry finished UHMS has smooth surface without cracks or shrinkage deformation.

Dry/wet UHMS foam sample photo
Dry/wet UHMS foam sample photo

Thermal Stability (TGA Test Data)

  • Initial decomposition temperature rises from 200.35°C (pure UF) to 224.18°C
  • 600°C carbon residual rate: 36.01% (vs 23.09% for unmodified UF)

HSN nano silica forms heat insulation barrier to delay polymer thermal chain scission.

Industrial Application Scenarios of UHMS UF-HSN Foam Absorbent

  • Agricultural Soil Water Retention Agent
     
    Mix UHMS foam with dry farmland soil; slow-release water reduces irrigation frequency, improves drought resistance of crops, fully biodegradable without plastic residue pollution.
  • Industrial Liquid Spill Absorption Material
     
    Absorb leaked neutral water-based chemical liquid, workshop wastewater; reusable after drying, low disposal cost compared disposable polyacrylate SAP.
  • Ecological Restoration & Desert Greening
     
    Mix with sandy soil to lock rainwater, extend soil moisture retention period, promote vegetation root growth.
  • Civil Water Storage & Moisture Regulation Foam
     
    Green building interior humidity adjustment material, lightweight filling foam with simultaneous moisture absorption & release function.

Production Operation Guidelines & Cost Advantages

Optimized Full Industrial Formula

  • UF prepolymer base: 100 parts by mass
  • HPMC modifier: 6.4%
  • SDS foaming agent: 8.0%
  • MPS foam stabilizer: 8.0%
  • KH550 pretreated HSN nano silica: 6%
  • Curing agent (phosphoric acid): Appropriate amount to adjust pH=4.5–5.0
  • Optimal stirring speed: 3500 r/min, foaming time 20–30min
  • Drying condition: 25°C constant temperature oven, 24h full curing

Production Cost Benefits

  • Main raw material UF resin is low-cost industrial adhesive byproduct
  • HPMC comes from plant cellulose, HSN silica dosage only 6% with tiny additive cost
  • Recyclable 10 times, reduces single-use absorbent consumption, cuts long-term application cost
  • Complete biodegradation after service life, no soil microplastic pollution treatment fee

Key Production Notes

  • HSN must be ultrasonic dispersed with KH550 coupling agent to avoid agglomeration leading to foam crack
  • Stirring speed strictly controlled at 3500 r/min: too low causes large pores, too high breaks foam structure
  • Dry at room temperature only; high-temperature baking accelerates foam shrinkage and reduces absorption capacity
  • Store finished foam in sealed low-humidity warehouse to pre-absorb ambient moisture and weaken performance

Existing Limitations & Future Optimization Directions

Current Technical Defects

  • Poor absorption performance for strong acid/alkali liquid, only applicable neutral aqueous solution
  • Nano silica raw material slightly increases production cost vs pure HPMC foam
  • Long-term outdoor UV exposure slowly degrades composite foam network

Future R&D Trends

  • Compound biomass modifiers (starch, lignin) to replace partial HPMC for further cost reduction
  • Functional nano fillers (nano TiO₂, bentonite) to add antibacterial, heavy metal adsorption functions
  • UV light stabilizer modification to improve outdoor weather resistance for desert restoration use
  • Low-solid UF waste resin recycling formula to realize circular economy foam production

conclusion

Q1 What is the optimal HSN nano silica dosage for UF-HPMC foam absorbent?

A 6% mass fraction based on total resin system delivers balanced water absorption, mechanical strength and pulverization resistance; dosage above 8% forms excessive closed pores and sharply reduces liquid uptake capacity.

Q2 Why does KH550 pretreatment of nano silica matter?

A KH550 grafts amino groups on HSN surface, forms Si-O-C chemical bonds with UF/HPMC hydroxyl groups, eliminates nanoparticle agglomeration and uniformly distributes silica on foam pore walls to strengthen the crosslink network.

Q3 What’s the maximum water absorption rate of UHMS composite foam?

A Optimized formula absorbs up to 17.28g deionized water per gram of foam, with saline absorption reaching 11.06g/g, far exceeding single HPMC modified UFHM foam.

Q4 Can this UF cellulose foam degrade naturally in soil?

A Yes, UF and HPMC are biodegradable polymer chains; after 3–6 months buried in soil, composite foam gradually decomposes without residual microplastic pollution, ideal eco-friendly agricultural water retention material.

Q5 What stirring speed yields the best pore structure?

A 3500 r/min high-speed stirring creates uniform 200μm interconnected pores; too low speed causes oversized pores with thin fragile walls, overhigh shear force ruptures foam and reduces porosity.

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