Ep 23 — Polymer Industry: Plastic Identification and Blend Analysis

Series: Encyclopedia of Infrared Spectroscopy: From Principles to Practice
Chapter: Part 3 · Intermediate — Industry Applications
Target Audience: Plastic recycling plant QC, polymer modification engineers, product failure analysts
Prerequisites: Ep 14 (ATR), Ep 19 (Library Search), Ep 21 (IR Identification Strategy)
Reading Time: About 45 minutes

Introduction: The Fate of a Truckload of "Unknown Plastics"

In March 2024, a recycling plant in Zhejiang received a truckload of imported "engineering plastic scraps" that the seller claimed to be "PC/ABS alloy" at a price of 18,000 RMB/ton. However, after granulation and injection molding, the samples were brittle and had a hazy surface, completely inconsistent with the expected performance of PC/ABS [1].

The factory lab scanned it with ATR-FTIR: the spectrum indeed showed characteristic peaks of PC (polycarbonate) at 1770 cm⁻¹ and 1230 cm⁻¹, but the characteristic butadiene double bonds (910, 965 cm⁻¹) of ABS were barely visible. Instead, distinct styrene homopolymer peaks appeared at 700–760 cm⁻¹ — this was actually a cheap counterfeit of PC blended with HIPS (high-impact polystyrene) [1][2].

At market prices, PC/ABS costs 26,000 RMB/ton, while PC/HIPS costs 14,000 RMB/ton — a difference of nearly double. An IR spectrum saved the plant a loss of 70,000 RMB. Since then, the factory subjects every incoming batch to ATR-FTIR, getting results in 2 minutes, far more accurate than traditional "density + burning" methods.

"ATR-FTIR has become the de facto standard for incoming plastics inspection in recycling and compounding industries, offering rapid identification without sample preparation."
—— Hummel S, Atlas of Plastics Additives [3]

Plastics are one of the most widely applied areas of infrared spectroscopy. In this episode, we will systematically build a rapid identification capability for common plastics, master strategies for distinguishing blends and copolymers, and conduct a complete practical identification of an unknown plastic fragment.

1. Why FTIR is the "Golden Tool" for Plastic Identification?

1.1 Three Major Scenarios for Plastic Identification

1.2 FTIR vs Other Plastic Identification Methods

💡 Industry status: Modern plastic recycling and compounding plants are almost all equipped with ATR-FTIR; some large recycling sorting lines even introduce online NIR sorters, but final confirmation still relies on mid-infrared ATR [4].

2. FTIR Quick Reference Table for Nine Common Plastics

2.1 Quick Reference Table (Arranged from High to Low Main Peak Positions)

The following table summarizes the characteristic FTIR peaks of the nine most common polymers in the plastics industry [3][5][6]:

Table 1: FTIR characteristic peaks of nine common plastics (data sources: Hummel [3], Socrates [5], Haslam et al. [6])

2.2 Detailed Interpretation of Each Plastic

2.2.1 Polyethylene (PE)

PE is the simplest polymer in structure — a pure -CH₂- chain, with a "clean" IR spectrum [3][5]:

• 2915, 2848 cm⁻¹: CH₂ asymmetric/symmetric stretching
• 1472, 1463 cm⁻¹: CH₂ scissoring bending
• 730, 720 cm⁻¹: CH₂ in-plane rocking (identification peaks), splitting into a doublet in long-chain crystalline form

🔗 Extension: The C-H stretching peaks of PE at 2915/2848 cm⁻¹ are the typical region for alkyl C-H. You can check the alkyl C-H functional group page at ftir.fun — this page shows 2920, 2850 cm⁻¹ as common C-H stretching peak positions [7].

Distinction between LDPE and HDPE [3]:

• LDPE (low density): The 1472/1463 doublet is less resolved (lower crystallinity)
• HDPE (high density): The 1472/1463 doublet is sharp (higher crystallinity)
• LLDPE: Spectrum similar to LDPE; DSC can aid distinction

2.2.2 Polypropylene (PP)

PP has one more methyl side chain than PE [3][5]:

• 2950, 2917, 2838 cm⁻¹: CH₃, CH₂ stretching
• 1376 cm⁻¹: CH₃ symmetric bending (identification peak)
• 1167, 973, 841 cm⁻¹: Isotactic PP (iPP) crystallization bands

Differentiation of iPP vs aPP [3]:

• Isotactic PP: sharp crystalline bands at 998, 973, 841, 809 cm⁻¹
• Atactic PP (aPP): these bands disappear or become very weak

2.2.3 Polystyrene (PS)

PS is easily identified in FTIR spectra due to the benzene ring side group [3][5]:

• 3080, 3060, 3026 cm⁻¹: aromatic C-H stretching (above 3000 cm⁻¹)
• 2924, 2850 cm⁻¹: aliphatic C-H
• 1601, 1493, 1452 cm⁻¹: benzene ring C=C skeleton
• 757, 700 cm⁻¹: monosubstituted benzene C-H out-of-plane bending (most diagnostic peaks)

💡 Key observation: The doublet at 700/757 cm⁻¹ in PS appears in almost all monosubstituted benzene compounds — this is the "fingerprint" for identifying styrene-containing polymers such as PS, HIPS, ABS, SBR, etc.

2.2.4 Polyvinyl chloride (PVC)

PVC contains C-Cl bonds, with unique IR features [3][5]:

• 690, 615 cm⁻¹: C-Cl stretching (diagnostic peaks)
• 1255, 1330 cm⁻¹: CH-Cl bending
• 1425 cm⁻¹: CH₂ scissoring
• 960 cm⁻¹: CH out-of-plane bending

Note: Pure PVC shows almost no C=O peak; if a peak appears at 1720 cm⁻¹, it may indicate plasticizers (e.g., DOP) or degradation products (see Ep 24).

2.2.5 Polyethylene terephthalate (PET)

PET is a typical polyester with rich IR features [3][5]:

• 1714 cm⁻¹: ester C=O stretching (diagnostic peak)
• 1240, 1100, 1020 cm⁻¹: C-O-C stretching
• 1410, 1340 cm⁻¹: O-H bending (related to benzene ring ortho position)
• 870, 725 cm⁻¹: benzene C-H out-of-plane bending (para-substitution characteristic)

🔗 Extension: The C=O stretching at 1714 cm⁻¹ in PET is characteristic of ester groups. On the ester functional group page at ftir.fun, ester C=O typically appears at 1720–1750 cm⁻¹ — PET's 1714 cm⁻¹ is slightly lower than typical esters due to benzene ring conjugation and hydrogen bonding [8].

2.2.6 Polyamide (PA, Nylon)

PA (e.g., PA6, PA66) contains amide groups [3][5]:

• 3300 cm⁻¹: N-H stretching (shifted lower and broadened due to hydrogen bonding)
• 3070 cm⁻¹: N-H stretching overtone
• 1635 cm⁻¹: Amide I (C=O stretching) (diagnostic peak)
• 1540 cm⁻¹: Amide II (N-H bending + C-N stretching) (diagnostic peak)
• 1265 cm⁻¹: Amide III

🔗 Extension: The doublet at 1635 and 1540 cm⁻¹ in PA is typical of Amide I and Amide II. On the amide functional group page at ftir.fun, 1650 and 1550 cm⁻¹ are the two common amide frequencies; near 1540 cm⁻¹, Amide II bands are also frequently recorded (support counts vary with library updates) [9].

Differentiation of PA6 vs PA66 [3]:

• Overall spectra are very similar
• PA6 has a strong peak at 935 cm⁻¹ (crystalline band), while PA66 is weaker
• DSC melting point measurement is needed for confirmation (PA6 ~220°C, PA66 ~265°C)

2.2.7 Polycarbonate (PC)

PC (bisphenol A type) has a unique ester-benzene ring structure [3][5]:

• 1774 cm⁻¹: C=O stretching (diagnostic peak, significantly higher than ordinary esters)
• 1503, 1410 cm⁻¹: benzene ring C=C
• 1230, 1190 cm⁻¹: C-O-C stretching
• 830, 760 cm⁻¹: benzene ring C-H out-of-plane bending (bisphenol A characteristic)

Why does PC's C=O appear at 1774 cm⁻¹ instead of the typical 1735 cm⁻¹? [5]

• The carbonate group (-O-CO-O-) has oxygen on both sides, with inductive effect increasing the C=O force constant
• Conjugation effect from adjacent benzene rings is weak
• Combined effect shifts the C=O frequency upward

2.2.8 Polymethyl methacrylate (PMMA)

Features of PMMA (acrylic) [3][5]:

• 1730 cm⁻¹: ester C=O stretching (diagnostic peak)
• 1240, 1190, 1148 cm⁻¹: C-O-C asymmetric stretching
• 2995, 2950, 1485, 1440 cm⁻¹: CH₃, CH₂
• 1385 cm⁻¹: CH₃ symmetric bending (characteristic of α-methyl adjacent to double bond)
• 750 cm⁻¹: CH₂ rocking

2.2.9 ABS (Acrylonitrile-Butadiene-Styrene)

ABS is a terpolymer; its IR spectrum combines features of all three components [3]:

• 2237 cm⁻¹: acrylonitrile C≡N stretching (diagnostic peak)
• 966 cm⁻¹: butadiene trans CH=CH out-of-plane bending
• 910 cm⁻¹: butadiene vinyl CH₂=CH out-of-plane bending
• 757, 700 cm⁻¹: styrene monosubstituted benzene
• 1601, 1493 cm⁻¹: benzene ring C=C

⚠️ Important: The butadiene content in ABS may vary due to aging or formulation adjustments; the intensity of peaks at 910/966 cm⁻¹ can serve as an indicator of rubber phase content.

III. Practical Advantages of ATR for Rapid Plastic Testing

3.1 Why is ATR the First Choice for Plastic Analysis?

Plastics are typical solid samples, and most are insoluble in common solvents. Conventional transmission methods pose difficulties [3][4]:

• KBr pellet: plastics are hard to grind, and heating may alter structure
• Film method: requires hot pressing or solvent casting, destructive
• Liquid cell: plastics are insoluble, cannot be used

ATR excels in these aspects [4]:

① No Sample Preparation Required

• Simply place the plastic piece directly on the diamond crystal
• Suitable for blocks, sheets, powders, granules
• Measurement time 1–2 minutes

② Non-Destructive

• Sample can be preserved as evidence or for retesting after measurement
• Suitable for "evidence samples" in failure analysis

③ Surface Analysis Capability

• ATR penetration depth 0.5–5 μm, specifically for surface analysis
• Ideal for analyzing coatings, contamination, and aging layers on plastic surfaces

④ Good Reproducibility

• Pressure mechanism ensures consistent contact
• Far superior reproducibility compared to KBr pellets

3.2 Practical Tips for ATR Testing of Plastics

① Sample Preparation

• Cut a flat small piece (approx. 5×5 mm)
• Surface should be smooth and free of grease
• For granules, use a blade to create a flat surface
• Large items (e.g., plastic drums) can be measured on-site with a portable ATR

② Contact Pressure

• Diamond ATR can apply 10–50 N pressure
• Hard plastics (PC, PMMA, PS) require higher pressure
• Soft plastics (PE, PP flexible) only need light pressure

③ Crystal Selection

• Diamond: general-purpose choice
• ZnSe: avoid diamond's absorption band at 2700–1800 cm⁻¹ (when measuring C≡N at 2237 cm⁻¹)
• Ge: for high refractive index samples (e.g., carbon-black-filled rubber)

④ Watch for Fillers

• Inorganic fillers such as glass fiber, talc, CaCO₃ have IR features that mix with the polymer
• Need to identify filler peaks (see Section VI)

3.3 Standard ATR Operation Procedure

   Incoming Sample
       │
       ▼
   Cut a flat small piece (5×5 mm)
       │
       ▼
   Clean diamond ATR crystal (wipe with ethanol)
       │
       ▼
   Collect background (when crystal is clean)
       │
       ▼
   Place sample → Apply pressure
       │
       ▼
   Collect spectrum (4 cm⁻¹, 16 scans)
       │
       ▼
   ATR correction (if matching with transmission library)
       │
       ▼
   Library search + manual interpretation
       │
       ▼
   Determine plastic type

Figure 1: Standard ATR rapid plastic testing procedure

IV. Strategies for Differentiating Blends and Copolymers

4.1 Blends vs Copolymers: Can FTIR Differentiate?

Problem: PC/ABS alloy (blend) and PC-g-ABS (graft copolymer) have nearly identical FTIR spectra. How to distinguish?

Answer: FTIR cannot directly distinguish blends from copolymers at the chemical bond level—because both contain the same functional groups and vibrational modes. However, indirect inference can be made through the following strategies [3][10]:

① Subtle differences in characteristic peak positions

Some copolymers due to molecular-level mixing exhibit dipole coupling or conformational changes, causing slight peak shifts or splitting.

② Semi-quantitative analysis

The ratio of two components in a blend can be estimated by the characteristic peak area ratio and compared with the "standard ratio" of the copolymer.

③ Extraction and separation method

• Blends can be selectively extracted with solvents (e.g., CH₂Cl₂ dissolves PC in PC/ABS)
• Copolymers cannot be separated due to chemical bonding
• Infrared analysis after separation can determine whether it is a blend or copolymer

④ DSC assistance

• Blend: two independent Tg values (e.g., PC Tg=150°C, PS Tg=100°C)
• Copolymer: usually only one broad Tg (between the two components)

4.2 "Fingerprint Strategy" for Blend Identification

Although FTIR is difficult to directly distinguish blends vs copolymers, it is very good at identifying the components of blends [3][10]:

Strategy 1: Characteristic peak superposition method

Blend spectrum ≈ Spectrum of component A + Spectrum of component B (linear superposition)

Example: In the spectrum of PC/ABS alloy, one can identify [3]:

• PC features: 1774 cm⁻¹ (C=O), 1230 cm⁻¹ (C-O-C)
• ABS features: 2237 cm⁻¹ (C≡N), 700/757 cm⁻¹ (benzene ring)

Strategy 2: Relative peak intensity ratio quantification

   A1774/A700 = K · [PC]/[ABS]

A working curve can be established using blends of known ratios to semi-quantitatively estimate component proportions.

Strategy 3: Difference spectrum method

If the main component is known, the main component spectrum can be subtracted to observe residual peaks—this is an effective method for detecting small amounts of minor components.

4.3 Quick reference of common plastic blends

5. Infrared Characteristics of Fillers

5.1 Infrared "Fingerprints" of Common Fillers

Plastic modification often involves adding inorganic fillers to enhance performance. These fillers have characteristic absorptions in the mid-infrared region of 4000–400 cm⁻¹ [3][11]:

Table 2: Infrared characteristics of common fillers (Data sources: Hummel [3], Liang et al. [11])

5.2 Tips for Identifying Filler Interference

① Strong peaks appearing in the "peak-free region" of polymers

• Polymers usually have few peaks around 1100–950 cm⁻¹ (except PET, PA, etc., which contain C-O)
• If a strong broad peak appears in this region, it is mostly SiO₂ or glass fiber
• Strong peaks at 700–500 cm⁻¹ are mostly TiO₂ or BaSO₄

② O-H peaks in the high wavenumber region

• 3400 cm⁻¹ (broad) → possibly ATH, MDH, kaolin and other hydroxyl-containing fillers
• 3695, 3677 cm⁻¹ (sharp) → characteristic of talc, kaolin, and other layered silicates

③ Sharp peaks unrelated to polymers

• 875, 712 cm⁻¹ (CaCO₃ doublet)
• 635, 610 cm⁻¹ (BaSO₄ doublet)
• These sharp peaks are "independent" signals of fillers

5.3 Quantitative Estimation of Filler Content

Filler content can be accurately determined by TGA (thermogravimetric analysis), but ATR-FTIR can provide semi-quantitative estimation [3][11]:

Method: Filler characteristic peak area / Polymer characteristic peak area = K · Filler content

Case: PP + glass fiber (GF)

• Measure the peak area of GF at 1050 cm⁻¹ $A_{GF}$
• Measure the peak area of PP at 1376 cm⁻¹ $A_{PP}$
• Working curve: $A{GF}/A{PP} = K \cdot w_{GF}$
• Establish the curve using standards with known GF contents of 10%, 20%, 30%.

Note: ATR is a surface analysis technique; when filler distribution is uneven, a single measurement may not represent the bulk.

6. Practical Case: Identifying an Unknown Plastic Fragment

6.1 Case Background

A hard plastic fragment of approximately 3×3 cm was received, semi-translucent milky white, from a failed part complained by a customer. The request was to identify the material and determine if it is the specified grade PC/ABS.

6.2 Identification Process

Step 1: Preliminary observation

• High hardness (cannot be scratched by fingernail)
• Density approximately 1.1–1.2 g/cm³ (sink/float test in water)
• Mild styrene odor upon burning
• Preliminary judgment: Possibly PC/ABS or HIPS series

Step 2: ATR-FTIR measurement

• Cut a small flat piece
• Diamond ATR measurement, 4 cm⁻¹, 32 scans
• ATR correction followed by library search

Step 3: Spectrum interpretation

   Wavenumber (cm⁻¹)   Assignment          Intensity
   ───────────────────────────────────────────────────
   3026                Aromatic C-H stretch   medium
   2924                Aliphatic C-H stretch  medium
   1774                PC C=O                 strong ← PC characteristic!
   1601                Benzene ring C=C       medium
   1493                Benzene ring C=C       medium
   1230                PC C-O-C               strong
   1185                PC C-O-C               medium
   1165                PC                     medium
   830                 Bisphenol A benzene ring medium
   760                 Benzene ring out-of-plane strong
   700                 Monosubstituted benzene strong ← styrene characteristic
   ───────────────────────────────────────────────────
   2237                C≡N stretch            absent ← missing AN in ABS!

966 Butadiene No ← missing B in ABS!
910 Butadiene No
```

Step 4: Determination

• PC characteristic peaks present (1774, 1230, 830 cm⁻¹) → Contains PC
• Styrene characteristic peaks present (700, 757, 1601 cm⁻¹) → Contains styrene units
• Missing C≡N 2237 cm⁻¹ → No acrylonitrile
• Missing butadiene 966/910 cm⁻¹ → No butadiene
• Conclusion: PC/PS blend (i.e., PC/HIPS or PC/GPPS), not the required PC/ABS

Step 5: Library search verification

• ATR corrected library search
• Hit: PC + PS blend (match factor 0.92)
• Further confirmation: DSC shows two Tg (150°C PC + 100°C PS), confirming blend not copolymer

6.3 Case Lessons

1. Looking at only one characteristic peak is insufficient

• If only the 700 cm⁻¹ peak were examined, it would be misidentified as PS
• Must simultaneously observe 1774 cm⁻¹ (PC) and 2237 cm⁻¹ (AN) for accurate determination

2. The "absence" of a peak is also informative

• The absence of 2237 cm⁻¹ is key to ruling out ABS
• In IR spectra, "should be present but absent" and "unexpected appearance" are equally diagnostic

3. Blend identification requires complementary techniques

• DSC measures Tg to distinguish blend vs. copolymer
• TGA measures filler content
• TMA measures thermal expansion

📷 Figure 2: FTIR spectra comparison of PC/ABS and PC/PS blends
Source: Hummel Atlas of Plastics Additives [3]
https://www.wiley.com/en-us/A…

7. Infrared Sorting in Plastics Recycling

7.1 Online Near-Infrared Sorting (NIR Sorting)

Large-scale recycling sorting lines commonly use online NIR automatic classification [4][12]:

• Conveyor belt transports fragments at high speed
• Line array NIR spectrometer scans each piece of plastic
• Material identified via reflectance spectrum
• High-pressure air jets divert different materials

Advantages: Sorting hundreds of pieces per second, much faster than manual sorting
Limitations:

• Black plastics (carbon black absorbs NIR) cannot be sorted — the biggest challenge in the industry
• Only surface analysis; coatings can interfere

7.2 Challenges in Identifying Black Plastics

Carbon black absorbs nearly all NIR, making NIR sorting impossible [12]. Common solutions:

① Mid-infrared ATR: Carbon black also absorbs MIR, but MIR provides rich information as a supplement
② Density method: PE/PP < 1, PS > 1, PVC > 1.3
③ X-ray fluorescence (XRF): Identifies PVC, flame-retardant plastics via Cl, Br, etc.
④ Terahertz spectroscopy: Can penetrate black plastics

💡 Industry frontier: Recent developments in hyperspectral imaging combined with machine learning have begun to identify some black plastics (relying on subtle differences in reflectivity) [12].

8. Industry Experience and "Pitfall" Records

8.1 Pitfall 1: Surface Contamination Leading to Misidentification

Case [1]: A plastic part had oil on the surface; ATR showed a strong peak at 1740 cm⁻¹, misidentified as "containing polyester." After cleaning the surface and re-measuring, the 1740 cm⁻¹ peak disappeared — it was mold release agent (stearate ester) residue.

Lesson:

• ATR is surface analysis; surface contamination affects the result first
• Wipe the sample surface with ethanol before measurement
• If necessary, cut a fresh cross-section for measurement

8.2 Pitfall 2: Filler Peaks Misidentified as Polymer Peaks

Case [11]: A PP injection-molded part contained 30% talc; a strong peak at 1015 cm⁻¹ in ATR spectrum was misidentified by a novice as "ester C-O," incorrectly concluding "contains PET."

Lesson:

• 1015 cm⁻¹ (talc), 1050 cm⁻¹ (glass fiber), 1100 cm⁻¹ (SiO₂) are all filler peaks
• When analyzing spectra, first identify characteristic filler peaks
• If necessary, burn off ash (550°C) to isolate fillers for separate measurement

8.3 Pitfall 3: Relying Solely on Library Search Without Manual Interpretation

Case: Library search of an ABS sample hit "styrene-butadiene rubber (SBR)" with match factor 0.85. The novice reported it as "SBR." In reality, the butadiene-styrene units in ABS are spectrally similar to SBR.

Lesson:

• The HQI value from library search is not a "confirmation"
• Must perform manual interpretation, especially diagnostic peaks (C≡N, etc.)
• Spectra of blends are additive; a single library search may hit the major component, missing the minor one

8.4 Pitfall 4: Ignoring Effects of Aging

Case: Outdoor PP parts showed a weak peak at 1715 cm⁻¹ in ATR spectrum, which was ignored. Actually, it was carbonyl groups from photo-oxidative aging of PP (see Ep 24).

Lesson:

• Weak peaks in the 1710–1740 cm⁻¹ region should raise suspicion of aging or additives
• Broad peak at 3400 cm⁻¹ is also a sign of aging (O-H formation)
• Outdoor samples should also report aging degree

Summary of This Episode

Questions

1. You receive an opaque white hard plastic. ATR spectrum shows peaks at 1774, 1230, 830, 700, 757 cm⁻¹, but 2237 cm⁻¹ is absent. Is this PC/ABS? Why? Provide the basis for determination.

2. An injection-molded part contains 30% glass fiber and 70% PA66. The ATR spectrum shows a strong broad peak at 1050 cm⁻¹ and double peaks at 1635/1540 cm⁻¹. Design a semi-quantitative method to estimate the glass fiber content.

3. PE, PP, and PS all have C-H stretching peaks at 2920–2850 cm⁻¹. How can you distinguish them using only these peaks? Refer to ftir.fun alkyl C-H functional group page for explanation.

4. An ATR spectrum of a PC part shows, in addition to PC characteristic peaks, a weak peak at 1715 cm⁻¹ and a broad peak at 3400 cm⁻¹. Based on this episode and the preview of Ep 24, determine possible causes and what further tests are needed.

5. Black plastics cannot be sorted by NIR automatically. Compare the advantages and disadvantages of ATR-FTIR, XRF, density method, and terahertz spectroscopy for sorting black plastics.

References

[1] China Plastics Processing Industry Association. Case Collection on Recycled Plastics Application and Quality Control. 2024.
https://www.cppia.com.cn/

[2] Eyerer P, Hirth T, Elsner P (eds.). Polymer Engineering — Technology and Application. Springer, 2020. Chapter 12 (Polymer Analysis).

[3] Hummel S. Atlas of Plastics Additives: Analysis by IR and Raman Spectroscopy. 2nd ed. Springer, 2002. ISBN: 978-3-540-43402-2.

[4] Beigbeder J et al. "Near-Infrared Spectroscopy for Sorting of Post-Consumer Plastics: A Review." Waste Management, 2021, 136: 199–211. DOI:10.1016/j.wasman.2021.10.005.

[5] Socrates G. Infrared and Raman Characteristic Group Frequencies. 3rd ed. Wiley, 2004. Chapters 5–9.

[6] Haslam J, Willis H A, Squirrell D C M. Identification and Analysis of Plastics. 2nd ed. Butterworth-Heinemann, 1972.

[7] ftir.fun. "Alkyl C-H — FTIR absorption peaks and assignments." FTIR Functional Group Database.
https://ftir.fun/ir/group/alk…

[8] ftir.fun. "Ester — FTIR absorption peaks and assignments." FTIR Functional Group Database.
https://ftir.fun/ir/group/est…

[9] ftir.fun. "Amide — FTIR absorption peaks and assignments." FTIR Functional Group Database.
https://ftir.fun/ir/group/ami…

[10] Stuart B H. Polymer Analysis. John Wiley & Sons, 2002. Chapter 4 (Vibrational Spectroscopy).

[11] Liang J Z, Li R K Y, Tjong S C. "Morphology and Tensile Strength of Talc-Filled Polypropylene Composites." Polymer Composites, 2000, 21(5): 797–805. DOI:10.1002/pc.10224.

[12] Küppers S et al. "Hyperspectral Imaging for Sorting of Black Plastics." Recycling, 2023, 8(3): 47. DOI:10.3390/recycling8030047.

Next Episode Preview: Ep 24 — Polymer Industry: Degradation and Aging Assessment
We will continue to delve into the polymer field, focusing on why plastics degrade — infrared characteristic products of photo-oxidation and thermal oxidation, measurement of carbonyl index, hydrolysis aging monitoring of polyurethane/polyamide, and a practical evaluation case of outdoor PE film aging over 5 years.