In the pulp and paper industry, kraft (sulphate) pulping is known for its characteristic product properties. Which description best captures the typical qualities of paper pulp produced by the kraft/sulphate process?

Introduction / Context:
The kraft (sulphate) process is the most widely used chemical pulping method. It dissolves lignin while preserving cellulose fibers, producing a robust pulp widely used for packaging grades, sack paper, and linerboard where strength is paramount.

Given Data / Assumptions:

• Pulp is produced by digesting wood chips in white liquor (NaOH and Na2S).
• Unbleached kraft pulp exits the digester with residual lignin (dark color).
• Kraft pulps are typically stronger than sulfite or mechanical pulps of similar fiber source.

Concept / Approach:

Alkaline sulphide cooking cleaves lignin linkages while minimizing cellulose degradation. This yields long fibers with high degree of polymerization and lower fines generation, which together improve tensile, burst, and tear indices. Color is secondary and typically dark unless followed by multi-stage bleaching.

Step-by-Step Solution:

Verification / Alternative check:

Industrial use patterns confirm: kraft dominates in containerboard and sack papers, where high tear and tensile strength are required. Bleached grades exist but require multi-stage sequences (e.g., ECF/TCF), evidencing that “easy one-stage bleaching” is inaccurate.

Why Other Options Are Wrong:

Bleached easily / Naturally light-colored: Unbleached kraft is dark; effective bleaching needs multiple stages. Dull white without processing: Also incorrect; color before bleaching is brown/dark, not white.

Common Pitfalls:

Confusing kraft with sulfite pulps (naturally lighter) or mechanical pulps (higher yield but lower strength). Assuming bleaching is trivial for kraft.

Final Answer:

Strong, long-fibered pulp with high tear and tensile strength