Why Polyester Bottle Flake / Unsaturated Resin Can't Do Without Isophthalic Acid (PIA)? From Molecular Structure to the Industry Chain

Column: Technical Primer / Industry Watch | Featured Product: Isophthalic Acid (Isophthalic Acid, PIA / IPA) | Downstream: Polyester Bottle Flake / Unsaturated Polyester Resin / Coatings / Copolyester
Updated: late July 2026 | Haiyu Zhonglong Chemical

📑 Table of Contents

What Is Isophthalic Acid? — Starting from Molecular Structure
Production Process and Key Raw Materials (m-Xylene Liquid-Phase Oxidation / Hydrolysis / Bio-based)
Downstream Applications: Polyester Bottle Flake, Unsaturated Polyester Resin, Coatings, etc.
2025 Market Supply-Demand Overview and Price Trend
Industry Outlook
References and Data Sources

I. What Is Isophthalic Acid? — Starting from Molecular Structure

Isophthalic acid (Isophthalic Acid, PIA / IPA, CAS 121-91-5) systematic name 1,3-benzenedicarboxylic acid (also known as "isophthalic acid"), molecular formula C₈H₆O₄. It is one of the three isomers of benzenedicarboxylic acid (ortho/meta/para), and a single molecule links three important fine-chemical industry chains: polyester bottle flake, unsaturated resin, and coatings.

  1,3-C₆H₄(COOH)₂
  (The two carboxyl groups −COOH on the benzene ring are in the meta / 1,3 position, rather than the para position of PTA)

💡 Core Structural Features
• Typicalmeta-aromatic dicarboxylic acid: the benzene ring provides rigidity, heat resistance and chemical resistance, while the carboxyl groups at both ends provide difunctionality
• The two carboxyl groups are inthe meta position (1,3), and compared with the para position (PTA), its lower molecular symmetry disrupts the regularity of the polyester chain
• This "disrupting" property is exactly what makes it acopolymerization modifier core value: improving transparency, reducing crystallinity, and optimizing processability

1.1 Overview of Key Physicochemical Properties

Indicator	Value / Description
Molecular Formula	C₈H₆O₄
CAS No.	121-91-5
Appearance	White crystalline powder or needle-like crystals
Melting Point	Approx. 345–348 °C (readily sublimes)
Density	Approx. 1.54 g/cm³
Solubility	Readily soluble in alcohols and glacial acetic acid; slightly soluble in boiling water, insoluble in cold water; nearly insoluble in benzene and petroleum ether
Properties	Heat-resistant, hydrolysis-resistant, chemical-corrosion resistant; can undergo polycondensation with alcohols/amines, salt formation, and hydrogenation

Data sources: PubChem; ChemSpider; common physical-property parameters from the China Chemical Products Handbook

1.2 Why It Is the Modification Star of the "Benzenedicarboxylic Acid Family"

Isophthalic acid plays a triple role: it is thecopolymerization modifier for polyester bottle flake key third monomer, theunsaturated polyester resin (UPR) rigid skeleton unit, and also thealkyd resin / coating important raw material. A single C₈ molecule connects all three tracks — packaging, composite materials, and coatings — which is exactly its irreplaceable underlying logic.

II. Production Process and Key Raw Materials

2.1 Mainstream Process: m-Xylene Liquid-Phase Oxidation

The vast majority of global isophthalic acid uses this route:m-Xylene (MX) → with cobalt acetate as catalyst, acetaldehyde as promoter, and acetic acid as solvent, low-temperature liquid-phase oxidation at approx. 0.6 MPa and 120°C → isophthalic acid crystallization and refining. The process is mature and highly selective, and is currently the lowest-cost mainstream solution.

📊 Cost Perspective: m-Xylene (MX) is the core raw material of isophthalic acid — the MX price almost determines the cost center of PIA. In 2025, affected by refinery maintenance and other factors, the global average m-Xylene price year-on-year rose by approx. 15% to 1,100 USD/tonne (CFR China), providing strong cost support for downstream prices.

2.2 Other Process Routes

In addition to the mainstream oxidation method, industry also adoptsisophthalonitrile hydrolysis, m-xylene potassium permanganate oxidation and other auxiliary or alternative processes, used for the production of specific grades and high-end products.

2.3 Bio-based Route — Sustainability Direction

Producing from biomass feedstockbio-based isophthalic acid (Bio-IPA), which can significantly reduce the carbon footprint and meets the sustainable procurement demands of downstream packaging and coating industries, represents an important direction for the industry's green transformation.

✅ Green Progress Snapshot:
• Regulations and buyers drivebio-based IPA, to meet sustainability goals and increasingly stringent plastics policies
• Advances in oxidation process technology improve yield and reduce energy consumption, helping manufacturers hedge against raw-material fluctuations and compliance costs
• The EU REACH imposes registration requirements on isophthalic acid derivatives; high-volume categories must complete compliance dossiers by 2025

2.4 Comparison of Mainstream Process Routes

Route	Key Raw Materials	Features	Representative / Status
m-Xylene Oxidation	m-Xylene, cobalt acetate	Mature, high selectivity, low cost	Mainstream (Hengyi / Formosa / Yanshan)
Isophthalonitrile Hydrolysis	Isophthalonitrile	Suitable for specific grades	Auxiliary process
Bio-based Method	Biomass feedstock	Low-carbon, high value-added	Sustainability direction (demonstration)

Note: The above process descriptions are compiled from public technical literature and industry reports; industrial production is mainly based on m-xylene liquid-phase oxidation.

III. Downstream Applications: Polyester Bottle Flake, Unsaturated Polyester Resin, Coatings, etc.

3.1 Polyester Bottle Chip (PET Bottle Chip) — the Largest Domestic Downstream

In polyester bottle flake production, PTA and MEG are the main raw materials, and a certain proportion of isophthalic acid is added for copolymerization modification. It reduces the regularity of the polyester molecular chain, improving the processing and molding performance of preforms and enhancing bottle transparency. China is the world's largest producer/consumer/exporter of bottle flake, and PIA's consumption share in this field exceeds 40%, far higher than other downstream sectors.

3.2 Unsaturated Polyester Resin (UPR) — the Classic Global Mainstay

Isophthalic acid is anunsaturated polyester resin important intermediate, imparting higher heat resistance, corrosion resistance, and mechanical strength to products; it is widely used in fiberglass-reinforced plastic (FRP), sanitary ware, ships, pipes, building materials, etc. In the global demand structure, UPR is the traditional core outlet for PIA.

3.3 Alkyd Resins and Coatings

PIA is used to manufacturealkyd resins (coatings) and printing inks, improving coating adhesion, weather resistance, and gloss; it is a common component of industrial protective paints and coil coatings.

3.4 Other Applications

Copolyester (PETG, etc.): high-end copolyester that improves toughness and transparency
Polyester fiber dyeing modifier: improves dyeing performance and color fastness
Pharmaceuticals / Electronic Chemicals: extensions into high-performance materials and fine chemicals
Film / Engineering Plastics and other emerging uses

3.5 Downstream Demand Structure (Domestic vs Global)

Application Field	Share of Domestic Demand	Share of Global Demand	Remarks
Polyester Bottle Flake (PET)	~40%+	~60.6%	Mainstay in both global and domestic markets
Unsaturated Polyester Resin (UPR)	~20% or less	~19.5%	Low in domestic, classic globally
alkyd resin / coating	Remaining	Remaining	Coatings, inks
Copolyester / Other	Emerging	Emerging	Growth potential

⚠️ Structural Difference Warning: Domestic demand is "skewed toward polyester bottle flake," differing from the global "PET resin + UPR dual-engine" structure. The main reason is the huge scale of the domestic bottle flake industry and strong copolymerization-modification demand; meanwhile, insufficient domestic supply capacity has left the market reliant on imports for the long term — although the import dependence has fallen to 34.47%, it remains the core contradiction of the industry.

Data sources: Huanjing Industry Research Institute "China Isophthalic Acid Industry Report 2025-2031"; Zhiyan Consulting; Gongyan Industry Research Institute (2025); Reports and Data (2025)

IV. 2025 Market Supply-Demand Overview and Price Trend

4.1 Capacity and Supply-Demand Pattern

China is an important global producer and consumer of isophthalic acid. According to industry disclosures, domestic capacity in 2024 was approx. 550,000 tonnes (Hengyi Petrochemical 300,000 t, Ningbo Formosa 200,000 t, Yanshan Petrochemical 50,000 t); production 446,000 t (YoY +33.7%), apparent consumption 660,900 t (YoY +13.52%), the industry is in a "insufficient supply + import supplementation" pattern.
Market leadership is highly concentrated: Hengyi Petrochemical leads with 300,000 t capacity (approx. 55% share), Ningbo Formosa approx. 36%, Yanshan Petrochemical approx. 9%; the two leading companies together control over 90% of capacity, showing a typical oligopoly.

📊 Current Pattern Interpretation: Driven by the continuous growth of polyester bottle flake output, domestic PIA production and demand are rising in tandem, but capacity expansion is limited (zero new additions in 2022–2024), and import dependence remains at 34.47% — "strong demand, tight supply, import supplementation" is the current leitmotif.

4.2 Complete Price Chain: Upstream Raw Material → Isophthalic Acid → Downstream

m-Xylene MX 1,100$/t → Cobalt acetate catalytic oxidation → Isophthalic acid 7,000~8,900 yuan/t → Polyester bottle flake / UPR / Coatings → End products

4.3 Current Market Prices (2025, collected from public platforms, for reference only)

Item	Spec / Brand	Price Range (yuan/tonne)	Data Source / Date
2025 East China Monthly Average	2025-07	7,861 (MoM −1.77%, YoY −15.67%)	SCI99 2025-07
2025 East China Monthly Average	2025-10	7,389 (MoM −1.75%, YoY −12.23%)	Longzhong 2025-12
Spot negotiation	2025-12 East China	6,950–7,050	2025-10 East China
Spot negotiation	7,350–7,400	2024 Annual Average	Full-year average
8,881 (down 4.99% vs 2023)	Huanjing / Zhiyan 2024	Year High/Low	High 9,625 (May) / Low 8,100 (Nov–Dec)
8,881 (down 4.99% vs 2023)	Traders (early year)	Lotte Korea / Yanshan (Shandong)	High 9,625 (May) / Low 8,100 (Nov–Dec)
8,400 / 8,650–9,000	SunSirs 2025-02	Note: The above are data from public quotation platforms and industry institutions; actual transaction prices fluctuate due to payment terms, freight, and purchase volume; the year's (2024) high-low spread was approx. 1,525 yuan/tonne. Updated on 2026-07-29.	4.4 Cost Transmission and Supply-Demand Dynamics

① Upstream: Strong Support from m-Xylene

In 2025, the global average m-Xylene price rose approx. 15% YoY to 1,100 USD/tonne (CFR China), providing strong cost support for PIA from the raw-material side.

② Midstream: Loose Supply, Weak Prices
In 2025, major domestic units resumed production one after another, and supply increased steadily; however, downstream bottle flake and resin industries saw lower operating rates and weak purchasing enthusiasm, and factories kept conceding to promote orders, so the price center continued to move downward.

Daily Review Consensus
: Longzhong / SCI99 have repeatedly pointed out that isophthalic acid shows "

⚠️ ample supply + tightening demand" — factories find it hard to support prices, the negotiation center shifts downward, and the market falls into low-level consolidation.③ Supply-Demand: Import Supplementation + Rigid Demand Procurement In 2024, import volume was 234,600 t (YoY −12.89%), and external dependence dropped to 34.47% (a sharp decline from the 85% high in 2018); downstream mostly engages in "rigid-demand replenishment," and the transaction pace is weak.

④ Global Perspective: Regional Divergence
In 2025 Q2, China FOB Qingdao was approx. 1,036 USD/tonne (MoM −3.3%), and US CFR Texas approx. 1,194 USD/tonne (MoM −6.6%); Asia-Pacific demand accounts for 55.44% of the global total, making it the absolute main market.
💡
Procurement Suggestion

• Currently in a historically relatively low level + weak oscillation:
range, suitable for phased positioning rather than one-time large orders • Closely trackthe m-Xylene price
and the unit maintenance/restart rhythm — any variable may trigger short-term fluctuations • Domestic high-purity PIA is gradually replacing imports; it is recommended to first take samples for lab-trial comparison (bottle flake transparency, resin heat resistance)4.5 Recent One-Year Price Trend (Cross-verified with Public Data)
Time

Event

East China Mainstream Price (yuan/tonne)	Trend	2024-05	Year high
9,625	⚠ Stage high	2024-11/12	⚠ Year low
8,100	↓ Declining	Weak oscillation, center moving down	↓ 7,750–8,000 (monthly avg 7,861)
2025-07	↓ Weak and stable	Crude oil falling, negotiations continuing to drop	↓ 7,250–7,450 (monthly avg 7,389)
2025-10	↓ Continuing to fall	2025-12	↓ High supply, weak rigid demand
↓ Low level	V. Industry Outlook	6,950–7,050	↓ 💡 Five Major Trend Analyses

Direction

💡 Core Judgment

Impact	Sustained Demand Growth	Driven by rising polyester bottle flake output; expanding applications in pharmaceuticals/electronic chemicals
Mid-to-long-term demand increment	Green Production	Tightening environmental regulations; bio-based IPA and clean processes accelerating implementation
Opening high value-added tracks	High Performance	Improving preform processing and bottle transparency to meet high-end packaging
Improving profit structure	Accelerated Localization	Import dependence down to 34.47%, domestic technology rapidly improving
Large import-substitution space	Capacity Expansion	New capacity coming online in 2026–2027; China expected to reach 1.4 million tonnes by 2032
Reshaping supply pattern	One-sentence Summary	: In the short term, pressured by

✅ loose supply + low prices; in the long term, it will follow the four main lines of "demand growth, greening, high performance, and localization" to complete the leap from "import dependence" to "independent supply." Whoever first positions in bottle flake increment and bio-based high value-added will grasp the initiative of the next cycle.Figure: Isophthalic acid molecular structure and downstream industry chain applications (compiled by Haiyu Zhonglong, illustrative)VI. Contact Us

Need isophthalic acid (PIA) samples, bulk quotes, or technical documentation (COA / TDS / application advice)?

📌 Click the official account menu

"Online Inquiry"

📌 , or add our WeCom (enterprise WeChat), and the Haiyu Zhonglong Chemical team will provide you with: • High-purity isophthalic acid (multiple domestic brands available, bottle-flake grade / resin grade) • Supporting supply of polyester bottle flake / unsaturated resin raw materials
• Regular market updates and procurement-timing advice
📚 References
[1] Huanjing Industry Research Institute. 2025 China Isophthalic Acid Industry Development Status and Outlook [EB/OL].

📚 [2] Zhiyan Consulting. 2025 China Isophthalic Acid Industry Status and Development Trend Analysis [EB/OL].
[3] Gongyan Industry Research Institute. 2026–2032 Global and China Isophthalate Industry In-depth Survey [EB/OL].
[4] SCI99. Isophthalic Acid Monthly Review (2025-07 / 2025-10) [EB/OL]. 2025.
[5] Longzhong Information (Mysteel). Isophthalic Acid Daily/Weekly Review and Unit Dynamics [EB/OL]. 2025.
[6] Reports and Data. Isophthalic Acid Market Size, Share, Trends 2025–2035[EB/OL].
[7] ChemAnalyst. Global Isophthalic Acid Price Trends Q2 2025[EB/OL].
[8] Tonghuashun / NetEase. 2025 China Isophthalic Acid Industry: Import Dependence and Oligopoly Pattern [EB/OL].
[9] Hengyi Petrochemical 2024 Annual Report (PIA business revenue +90.85%) [EB/OL].
⚠️ The prices listed in this article are data collected from public platforms, for reference only, and do not constitute trading advice. Actual transactions should follow suppliers' real-time quotes. Academic and technical data are from publicly published literature, industry reports, and manufacturer disclosures.
Why Polyester / Beverage Bottles Can't Do Without PTA (Purified Terephthalic Acid)? From Molecular Structure to the Industry Chain

Column: Technical Primer / Industry Watch | Featured Product: Purified Terephthalic Acid (Purified Terephthalic Acid, PTA) | Downstream: Polyester Fiber (Polyester) / Bottle Chip / Film

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