Crystalline Fraction by WAXS

WAXS probes X-rays scattered at wide angles by regular atomic arrangements in crystalline domains. In semi-crystalline polymers, the scattering pattern contains:

Sharp crystalline peaks, arising from the ordered lattice
Broad amorphous scattering, originating from disordered regions

By separating these contributions, it is possible to determine the fraction of crystalline material within the polymer.

Typical measurable parameters include:

Crystalline fraction, based on integrated intensities of crystalline and amorphous contributions
Relative fractions of different crystalline phases, when multiple polymorphs are present (e.g., alpha vs. gamma)
Lattice spacing and crystalline domain characteristics, inferred from the position and width of the WAXS peaks

Figure 1. Crystallinity determination from experimental data using subtraction of the amorphous contribution (dashed line), revealing a crystalline fraction of 1.1%.

Laboratory WAXS instruments can quantify crystalline fractions from approximately 1% to 90%, with sensitivity extendable down to ~0.2% when accurate amorphous references or thermal protocols are available.

Crystallinity determination by WAXS applies to any polymer system exhibiting meaningful electron density contrast between crystalline and amorphous phases.

Typical materials include:

Polyolefins such as PE, PP, and their copolymers
High-performance polymers such as PEEK, PEKK, and related semi-crystalline engineering plastics
Polymer blends, composites, and filled systems
Films, fibers, molded components, or powders
Materials under thermal or mechanical treatment, including crystallization, melting, or annealing processes

Because the technique is non-destructive and requires minimal preparation, measurements can be performed on bulk samples, thin sections, or processed parts, as well as in situ under controlled temperature or environmental conditions.